| 1. |
- Bai, M. W., et al.
(författare)
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Different responses of the radial growth of the planted and natural forests to climate change in humid subtropical China
- 2020
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Ingår i: Geografiska Annaler Series a-Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 102:3, s. 235-246
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Tidskriftsartikel (refereegranskat)abstract
- China holds the world's largest area of planted forests, which play a crucial role in mitigating climate change. Knowledge gaps remain on the responses of the growth of planted forests to climate changes in China, particularly for their long-term changes. This study compared the long-term tree-ring growth patterns and their responses to climate between planted and natural forests. We developed four chronologies from two typical conifer species ofPinus massonianaandCunninghamia lanceolatafrom planted and natural forests in humid subtropical China. One chronology is to our knowledge the longest chronology from planted forests in China spanning since 1944. Tree growths of both natural and planted forests are generally limited by summer drought due to the hot and dry summer in this area. In general, tree rings of the natural forests are more sensitive to climate than planted forests as indicated by higher inter-series correlations, which agree with previous studies. The natural forests are more drought sensitive wheareas the planted forests are relatively more limited by temperature. TheC. lanceolataforests showed more significant correlations with the accumulated drought thanP. massonianafor both the natural and planted forests.
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| 2. |
- Chen, D., et al.
(författare)
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A tree-ring delta O-18 based reconstruction of East Asia summer monsoon over the past two centuries
- 2020
-
Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 15:6
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Tidskriftsartikel (refereegranskat)abstract
- The East Asian summer monsoon (EASM) exhibits considerable decadal variations since the late 20th century. Efforts to examine long-term behaviors and dynamics of the EASM are impeded largely due to the shortness of instrumental meteorological records. So far, reconstructions of the EASM with annual resolution from its core regions remain limited. We conduct the first 200-year robust EASM reconstruction based on tree-ring cellulose delta O-18 records derived from Pinus massoniana trees growing in the middle Yangtze River basin, one of the core EASM areas. The delta O-18 chronology accounts for 46.2% of the actual variation in an index of the EASM from 1948 to 2014. The reconstructed EASM indicates that the monsoon intensity was below average before the 1950s, peaked in the 1950s-1970s, and then began to decline. The reconstructed EASM is negatively correlated with the El Nino-Southern Oscillation (ENSO), but this teleconnection is dynamic through time, i.e. enhanced (reduced) ENSO variability coheres with strong (weak) EASM-ENSO connections. In addition, despite high ENSO variability since the 1980s, the EASM-ENSO relationship weakened possibly due to anthropogenic impact, particularly aerosol emissions.
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| 3. |
- Chen, Deliang, 1961, et al.
(författare)
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Hydroclimate changes over Sweden in the twentieth and twenty-first centuries: a millennium perspective
- 2021
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Ingår i: Geografiska Annaler: Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 103:2, s. 103-31
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Tidskriftsartikel (refereegranskat)abstract
- Climate change poses additional risks for natural and human systems including the hydrological cycle, leading to altered temporal and spatial variation of hydroclimatic conditions. This work assessed the current understanding of the dryness and wetness conditions in Sweden over the last two millenniums based on proxy and instrumental data, as well as climate model simulations and projections until the end of the twenty-first century. The assessment represents a summary of the existing literature concerning analysis of four selected indices for dry/wet conditions relating to precipitation, potential evapotranspiration (PET), and soil moisture (SPEI, PDSI [including scPDSI], SPI, and AI). SPEI considers both precipitation and PET and can show hydroclimatic conditions at different time scales. Therefore, it was chosen to summarize the past and future changes. A focus is put on dry conditions, as drought has strong influences on groundwater which is an important freshwater resource for Sweden. The millennium historical perspective reveals that the current climate is relatively wet and the future would become even wetter as a general wetting trend started some 120 years ago. However, there have been and will be large variations of both dry and wet conditions on short time scales, especially on decadal and interannual time scales. Further, the changes since the 1950s show a regional pattern with most significant wetting in the north, a slightly overall wetting in the south but a drying in central-eastern part including the island of Gotland since 1981. This pattern is broadly consistent with climate model projections for the future.
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| 4. |
- Chen, Deliang, 1961, et al.
(författare)
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Projecting future local precipitation and its extremes for Sweden
- 2015
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Ingår i: Geografiska Annaler. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 97:1, s. 25-39
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Tidskriftsartikel (refereegranskat)abstract
- A procedure to obtain future local precipitation characteristics focused on extreme conditions has been developed based on a weather generator. The method involves six major steps: (1) the weather generator was calibrated using observed daily precipitation at 220 Swedish stations during 1961–2004; (2) present and future daily precipitation characteristics for the Swedish stations from two global climate models, namely ECHAM5 and HadCM3, were used to calculate weather generator parameters for the present and future climates at global climate model spatial scales; (3) the ratio of the weather generator parameters for the present climate simulated by the global climate models to those calculated for each station falling into the global climate model grid box were computed for all the stations; (4) these ratios were also assumed to be valid in the future climate, that way the future parameters for each station for the global climate model projected future climate could be calculated; (5) using the estimated future parameters of the weather generator, the future daily precipitation at each station could be simulated by the weather generator; (6) the simulated daily precipitation was used to compute eight indices describing mean and extreme precipitation climates. The future mean and extreme precipitation characteristics at the stations under the Second Report on Emission Scenarios A2 scenario were obtained and presented. An overall increasing trend for frequency and intensity of the indices are identified for the majority of the stations studied. The developed downscaling methodology is relatively simple but useful in deriving local precipitation changes, including changes in the precipitation extremes.
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| 5. |
- Chen, Deliang, 1961, et al.
(författare)
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Recent Recovery of the Siberian High Intensity
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116
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Tidskriftsartikel (refereegranskat)abstract
- This study highlights the fast recovery of the wintertime Siberian High intensity (SHI) over the last two decades. The SHI showed a marked weakening trend from the 1970s to 1980s, leading to unprecedented low SHI in the early 1990s according to most observational data sets. This salient declining SHI trend, however, was sharply replaced by a fast recovery over the last two decades. Since the declining SHI trend has been considered as one of the plausible consequences of climate warming, the recent SHI recovery seemingly contradicts the continuous progression of climate warming in the Northern Hemisphere. We suggest that alleviated surface warming and decreased atmospheric stability in the central Siberia region, associated with an increase in Eurasian snow cover, in the recent two decades contributed to this rather unexpected SHI recovery. The prominent SHI change, however, is not reproduced by general circulation model (GCM) simulations used in the IPCC AR4. The GCMs indicate the steady weakening of the SHI for the entire 21st century, which is found to be associated with a decreasing Eurasian snow cover in the simulations. An improvement in predicting the future climate change in regional scale is desirable.
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| 6. |
- Chen, Deliang, 1961, et al.
(författare)
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Satellite measurements reveal strong anisotropy in spatial coherence of climate variations over the Tibet Plateau
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- This study uses high-resolution, long-term satellite observations to evaluate the spatial scales of the climate variations across the Tibet Plateau (TP). Both land surface temperature and precipitation observations of more than 10 years were analysed with a special attention to eight existing ice-core sites in the TP. The temporal correlation for the monthly or annual anomalies between any two points decreases exponentially with their spatial distance, and we used the e-folding decay constant to quantify the spatial scales. We found that the spatial scales are strongly direction-dependent, with distinctive patterns in the west-east and south-north orientations, for example. Meanwhile, in the same directions the scales are largely symmetric backward and forward. Focusing on the west-east and south-north directions, we found the spatial coherence in the first is generally stronger than in the second. The annual surface temperature had typical spatial scales of 302-480 km, while the annual precipitation showed smaller scales of 111-182 km. The majority of the eight ice-core sites exhibit scales much smaller than the typical scales over the TP as a whole. These results provide important observational basis for the selection of appropriate downscaling strategies, deployment of climate-data collection networks, and interpreting paleoclimate reconstructions.
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| 7. |
- Chen, Deliang, 1961, et al.
(författare)
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Spatial Interpolation of Daily Precipitation in China : 1951-2005
- 2010
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Ingår i: Advances in Atmospheric Sciences. - : Springer Science and Business Media LLC. - 0256-1530 .- 1861-9533. ; 27:6, s. 1221-1232
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Tidskriftsartikel (refereegranskat)abstract
- Climate research relies heavily on good quality instrumental data; for modeling efforts gridded data are needed. So far, relatively little effort has been made to create gridded climate data for China. This is especially true for high-resolution daily data. This work, focuses on identifying an accurate method to produce gridded daily precipitation in China based on the observed data at 753 stations for the period 1951-2005. Five interpolation methods, including ordinary nearest neighbor, local polynomial, radial basis function, inverse distance weighting, and ordinary kriging, have been used and compared. Cross-validation shows that the ordinary kriging based on seasonal semi-variograms gives the best performance, closely followed by the inverse distance weighting with a power of 2. Finally the ordinary kriging is chosen to interpolate the station data to a 18 kmx 18 km grid system covering the whole country. Precipitation for each 0.5A degrees x 0.5A degrees latitude-longitude block is then obtained by averaging the values at the grid nodes within the block. Owing to the higher station density in the eastern part of the country, the interpolation errors are much smaller than those in the west (west of 100A degrees E). Excluding 145 stations in the western region, the daily, monthly, and annual relative mean absolute errors of the interpolation for the remaining 608 stations are 74%, 29%, and 16%, respectively. The interpolated daily precipitation has been made available on the internet for the scientific community.
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| 8. |
- Chen, Deliang, 1961, et al.
(författare)
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Summary of a workshop on extreme weather events in a warming world organized by the Royal Swedish Academy of Sciences
- 2020
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Ingår i: Tellus Series B-Chemical and Physical Meteorology. - : Stockholm University Press. - 1600-0889 .- 0280-6509. ; 72:1
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is not only about changes in means of climatic variables such as temperature, precipitation and wind, but also their extreme values which are of critical importance to human society and ecosystems. To inspire the Swedish climate research community and to promote assessments of international research on past and future changes in extreme weather events against the global climate change background, the Earth Science Class of the Royal Swedish Academy of Sciences organized a workshop entitled 'Extreme weather events in a warming world' in 2019. This article summarizes and synthesizes the key points from the presentations and discussions of the workshop on changes in floods, droughts, heat waves, as well as on tropical cyclones and extratropical storms. In addition to reviewing past achievements in these research fields and identifying research gaps with a focus on Sweden, future challenges and opportunities for the Swedish climate research community are highlighted.
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| 9. |
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| 10. |
- Chen, Shiyin, et al.
(författare)
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Tree-ring recorded variations of 10 heavy metal elements over the past 168 years in southeastern China
- 2021
-
Ingår i: Elementa: Science of the Anthropocene. - : University of California Press. - 2325-1026. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Heavy metal pollution is a serious concern in the urban area of China. Understanding metal pollution history is crucial for setting up appropriate measures for pollution control. Herein, we report a record of concentrations of 10 heavy metals (Fe, Mn, Cu, Zn, Ni, Cr, Cd, Pb, Co, and Sr) in Pinus massoniana tree rings from Fuzhou City over the past 168 years, which represents the longest tree-ring chronology of heavy metals in China. The studied metals displayed contrasting distribution patterns. Among them, Mn and Sr showed the strongest migration trend with peak concentrations at the pith. Co, Cd, and Pb also showed distinctively high concentrations near the boundary between heartwood and sapwood. Ni, Cu, Cr, and Fe showed an increasing trend possibly due to migration toward bark caused by physiological activities and increasing tourism activities and traffic pollution. The other elements (Cr, Fe, and Zn) with low migration revealed the historical pollution possibly discharged by the Fuzhou Shipping Bureau and other anthropogenic activities. Strong correlations between Cu content and temperature were found, which provides an alternative tree-ring proxy for climate reconstruction. This study provides a long-term perspective of the joint impacts of physiological, environmental, and climatological factors on the concentrations of heavy metals in southeastern China.
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| 11. |
- Collier, Emily, et al.
(författare)
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The first ensemble of kilometer-scale simulations of a hydrological year over the third pole
- 2024
-
Ingår i: Climate Dynamics. - 0930-7575 .- 1432-0894.
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Tidskriftsartikel (refereegranskat)abstract
- An accurate understanding of the current and future water cycle over the Third Pole is of great societal importance, given the role this region plays as a water tower for densely populated areas downstream. An emerging and promising approach for skillful climate assessments over regions of complex terrain is kilometer-scale climate modeling. As a foundational step towards such simulations over the Third Pole, we present a multi-model and multi-physics ensemble of kilometer-scale regional simulations for the hydrological year of October 2019 to September 2020. The ensemble consists of 13 simulations performed by an international consortium of 10 research groups, configured with a horizontal grid spacing ranging from 2.2 to 4km covering all of the Third Pole region. These simulations are driven by ERA5 and are part of a Coordinated Regional Climate Downscaling EXperiment Flagship Pilot Study on Convection-Permitting Third Pole. The simulations are compared against available gridded and in-situ observations and remote-sensing data, to assess the performance and spread of the model ensemble compared to the driving reanalysis during the cold and warm seasons. Although ensemble evaluation is hindered by large differences between the gridded precipitation datasets used as a reference over this region, we show that the ensemble improves on many warm-season precipitation metrics compared with ERA5, including most wet-day and hour statistics, and also adds value in the representation of wet spells in both seasons. As such, the ensemble will provide an invaluable resource for future improvements in the process understanding of the hydroclimate of this remote but important region.
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| 12. |
- Dahl, Martin, 1984-, et al.
(författare)
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A 2,000-Year Record of Eelgrass (Zostera marina L.) : Colonization Shows Substantial Gains in Blue Carbon Storage and Nutrient Retention
- 2024
-
Ingår i: Global Biogeochemical Cycles. - : John Wiley & Sons. - 0886-6236 .- 1944-9224. ; 38:3
-
Tidskriftsartikel (refereegranskat)abstract
- Assessing historical environmental conditions linked to habitat colonization is important for understanding long-term resilience and improving conservation and restoration efforts. Such information is lacking for the seagrass Zostera marina, an important foundation species across cold-temperate coastal areas of the Northern Hemisphere. Here, we reconstructed environmental conditions during the last 14,000 years from sediment cores in two eelgrass (Z. marina) meadows along the Swedish west coast, with the main aims to identify the time frame of seagrass colonization and describe subsequent biogeochemical changes following establishment. Based on vegetation proxies (lipid biomarkers), eelgrass colonization occurred about 2,000 years ago after geomorphological changes that resulted in a shallow, sheltered environment favoring seagrass growth. Seagrass establishment led to up to 20- and 24-fold increases in sedimentary carbon and nitrogen accumulation rates, respectively. This demonstrates the capacity of seagrasses as efficient ecosystem engineers and their role in global change mitigation and adaptation through CO2 removal, and nutrient and sediment retention. By combining regional climate projections and landscape models, we assessed potential climate change effects on seagrass growth, productivity and distribution until 2100. These predictions showed that seagrass meadows are mostly at risk from increased sedimentation and hydrodynamic changes, while the impact from sea level rise alone might be of less importance in the studied area. This study showcases the positive feedback between seagrass colonization and environmental conditions, which holds promise for successful conservation and restoration efforts aimed at supporting climate change mitigation and adaptation, and the provision of several other crucial ecosystem services. © 2024. The Authors.
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| 13. |
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| 14. |
- Fang, Keyan, et al.
(författare)
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ENSO modulates wildfire activity in China
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- China is a key region for understanding fire activity and the drivers of its variability under strict fire suppression policies. Here, we present a detailed fire occurrence dataset for China, the Wildfire Atlas of China (WFAC; 2005-2018), based on continuous monitoring from multiple satellites and calibrated against field observations. We find that wildfires across China mostly occur in the winter season from January to April and those fire occurrences generally show a decreasing trend after reaching a peak in 2007. Most wildfires (84%) occur in subtropical China, with two distinct clusters in its southwestern and southeastern parts. In southeastern China, wildfires are mainly promoted by low precipitation and high diurnal temperature ranges, the combination of which dries out plant tissue and fuel. In southwestern China, wildfires are mainly promoted by warm conditions that enhance evaporation from litter and dormant plant tissues. We further find a fire occurrence dipole between southwestern and southeastern China that is modulated by the El Nino-Southern Oscillation (ENSO). Fire activity in China and its associations with climate are not well quantified at a local scale. Here, the authors present a detailed fire occurrence dataset for China and find a dipole fire pattern between southwestern and southeastern China that is modulated by the El Nino-Southern Oscillation (ENSO).
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| 15. |
- Fang, Keyan, et al.
(författare)
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Oceanic and atmospheric modes in the Pacific and Atlantic Oceans since the Little Ice Age (LIA): Towards a synthesis
- 2019
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 215, s. 293-307
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the variability of the oceanic and atmospheric modes from the Little Ice Age (LIA,similar to 1250 - 1850) to the present can help evaluate their behaviors under future warming scenarios. Numerous proxy-based reconstructions of the oceanic and atmospheric modes were presented. It is highly needed for a synthesis study to evaluate the existing reconstructions of the dominant oceanic and atmospheric modes since the LIA. We found that the El Nino-Southern Oscillation (ENSO) reconstructions are only robust on interannual and interdecadal scales, while the reconstructed Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO) are robust on multi-decadal (50-100 years) timescales. We generated synthesized ENSO, PDO and AMO reconstructions as the average of the existing reconstructions on the most suitable timescales identified using timescale dependent correlation methods. In the 20th century, the interannual variability and periodicity of the ENSO and the multi-decadal periodicity of the PDO and AMO were most pronounced. The ENSO shows the strongest multi-decadal periodicity from mid-18th century onwards, while the multi-decadal periodicity of the PDO and AMO was particularly low in the 18th century. Multi-decadal variations of the AMO showed a prompt and positive response to solar irradiation, while the ENSO showed a lagged and negative response to solar irradiation from the 18th century to the present. (C) 2019 Elsevier Ltd. All rights reserved.
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| 16. |
- Fang, Keyan, et al.
(författare)
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Synchronous multi-decadal climate variability of the whole Pacific areas revealed in tree rings since 1567
- 2018
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 13:2
-
Tidskriftsartikel (refereegranskat)abstract
- Oceanic and atmospheric patterns play a crucial role on modulating climate variability from interannual to multi-decadal timescales by, causing large-scale co-varying climate changes. The brevity of the existing instrumental records hinders the ability to recognize climate patterns before the industrial era, which can be alleviated by using proxies. Unfortunately, proxy based reconstructions of oceanic and atmospheric modes of the past millennia often have modest agreements with each other before the instrumental period, raising questions about the robustness of the reconstructions. To ensure the stability of climate signals in proxy data through time, we first identified tree-ring datasets from distant regions containing coherent variations in Asia and North America, and then interpreted their climate information. We found the multi-decadal covarying climate patterns of the middle and high latitudinal regions around the northern Pacific Ocean agreed quite well with the climate reconstructions of the tropical and southern Pacific areas. This indicates a synchronous variability at multi-decadal timescale of the past 430 years for the entire Pacific Ocean. This pattern is closely linked to the dominant mode of the Pacific sea surface temperature (SST) after removing the warming trend. This Pacific multi-decadal SST variability resembles the Interdecadal Pacific Oscillation (IPO).
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| 17. |
- Grundström, Maria, 1979, et al.
(författare)
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The relationship between birch pollen, air pollution and weather types and their effect on antihistamine purchase in two Swedish cities
- 2017
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Ingår i: Aerobiologia. - : Springer Science and Business Media LLC. - 0393-5965 .- 1573-3025. ; 33:4, s. 457-471
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 The Author(s)Exposure to elevated air pollution levels can aggravate pollen allergy symptoms. The aim of this study was to investigate the relationships between airborne birch (Betula) pollen, urban air pollutants NO2, O3 and PM10 and their effects on antihistamine demand in Gothenburg and Malmö, Sweden, 2006–2012. Further, the influence of large-scale weather pattern on pollen-/pollution-related risk, using Lamb weather types (LWTs), was analysed. Daily LWTs were obtained by comparing the atmospheric pressure over a 16-point grid system over southern Sweden (scale ~3000 km). They include two non-directional types, cyclonic (C) and anticyclonic (A) and eight directional types depending on the wind direction (N, NE, E…). Birch pollen levels were exceptionally high under LWTs E and SE in both cities. Furthermore, LWTs with dry and moderately calm meteorological character (A, NE, E, SE) were associated with strongly elevated air pollution (NO2 and PM10) in Gothenburg. For most weather situations in both cities, simultaneously high birch pollen together with high air pollution had larger over-the-counter (OTC) sales of antihistamines than situations with high birch pollen alone. LWTs NE, E, SE and S had the highest OTC sales in both cities. In Gothenburg, the city with a higher load of both birch pollen and air pollution, the higher OTC sales were especially obvious and indicate an increased effect on allergic symptoms from air pollution. Furthermore, Gothenburg LWTs A, NE, E and SE were associated with high pollen and air pollution levels and thus classified as high-risk weather types. In Malmö, corresponding high-risk LWTs were NE, E, SE and S. Furthermore, occurrence of high pollen and air pollutants as well as OTC sales correlated strongly with vapour pressure deficit and temperature in Gothenburg (much less so in Malmö). This provides evidence that the combination of meteorological properties associated with LWTs can explain high levels of birch pollen and air pollution. Our study shows that LWTs represent a useful tool for integrated daily air quality forecasting/warning.
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| 18. |
- He, J., et al.
(författare)
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Development and Evaluation of an Ensemble-Based Data Assimilation System for Regional Reanalysis Over the Tibetan Plateau and Surrounding Regions
- 2019
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Ingår i: Journal of Advances in Modeling Earth Systems. - 1942-2466. ; 11:8, s. 2503-2522
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Tidskriftsartikel (refereegranskat)abstract
- The Tibetan Plateau is regarded as the Earth's Third Pole, which is the source region of several major rivers that impact more 20% the world population. This high‐altitude region is reported to have been undergoing much greater rate of weather changes under global warming, but the existing reanalysis products are inadequate for depicting the state of the atmosphere, particularly with regard to the amount of precipitation and its diurnal cycle. An ensemble Kalman filter (EnKF) data assimilation system based on the limited‐area Weather Research and Forecasting (WRF) model was evaluated for use in developing a regional reanalysis over the Tibetan Plateau and the surrounding regions. A 3‐month prototype reanalysis over the summer months (June−August) of 2015 using WRF‐EnKF at a 30‐km grid spacing to assimilate nonradiance observations from the Global Telecommunications System was developed and evaluated against independent sounding and satellite observations in comparison to the ERA‐Interim and fifth European Centre for Medium‐Range Weather Forecasts Reanalysis (ERA5) global reanalysis. Results showed that both the posterior analysis and the subsequent 6‐ to 12‐hr WRF forecasts of the prototype regional reanalysis compared favorably with independent sounding observations, satellite‐based precipitation versus those from ERA‐Interim and ERA5 during the same period. In particular, the prototype regional reanalysis had clear advantages over the global reanalyses of ERA‐Interim and ERA5 in the analysis accuracy of atmospheric humidity, as well as in the subsequent downscale‐simulated precipitation intensity, spatial distribution, diurnal evolution, and extreme occurrence.
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| 19. |
- He, M. S., et al.
(författare)
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A delayed modulation of solar ultraviolet radiation on the COVID-19 transmission reflects an incubation period
- 2022
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Ingår i: Meteorological Applications. - : Wiley. - 1350-4827 .- 1469-8080. ; 29:5
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory experiments have revealed the meteorological sensitivity of the coronavirus disease 2019 (COVID-19) virus. However, no consensus has been reached about how outdoor meteorological conditions modulate the virus transmission as it is also constrained by non-meteorological conditions. Here, we identify the outbreak's evolution stage, constrained least by non-meteorological conditions, by searching the maximum correlation coefficient between the ultraviolet flux and the growth rate of cumulative confirmed cases at the country level. At this least-constrained stage, the cumulative cases count around 1300-3200, and the count's daily growth rate correlates with the ultraviolet flux and temperature significantly (correlation coefficients r = -0.54 +/- 0.09 and -0.39 +/- 0.10 at p<0.01$$ p, respectively), but not with precipitation, humidity, and wind. The ultraviolet correlation exhibits a delay of about 7 days, providing a meteorological measure of the incubation period. Our work reveals a seasonality of COVID-19 and a high risk of a pandemic resurgence in winter, implying a need for seasonal adaption in public policies.
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| 20. |
- Hu, Yumei, et al.
(författare)
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Winter hoar frost conditions on Swedish roads in a warming climate
- 2018
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38:12, s. 4345-4354
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Tidskriftsartikel (refereegranskat)abstract
- As one of the most common reasons for slippery roads in wintertime, hoar frost can reduce surface friction and affect traffic safety. The risk of winter road hoar frost is subjected to changes in the warming climate. A better understanding of these changes could lead to improved forecasting of hoar frost risk and provide information to policymakers in making climate adaptation strategies. In this work, the decadal variation in winter road hoar frost risk between 2000 and 2016 in Sweden was examined by using in situ observations from 244 stations in the Swedish Road Weather Information System. Results show that hoar frost risks have decreased in the south of Sweden (south of 59 degrees N), whilst increasing in central Sweden (approximately 59 degrees-65 degrees N). Hoar frost risk tends to increase (decrease) in regions where there is a relatively high (low) mean number of hoar frost risk days. Further analysis indicates that the strengthened winter North Atlantic Oscillation (NAO) over the last few decades, which resulted in warmer and wetter winters in Sweden, is the main cause of the changes. During strong positive NAO winters, the frequency of blocking anticyclones centred to the south-west of Sweden significantly decreased and led to more warm and moist air from south-west being transported to Sweden. The reduction in hoar frost risk in the southern part of Sweden is mainly due to an increase in road surface temperature, while the increasing hoar frost risk in central Sweden is dominated by the increase in relative humidity, which favours the occurrence of hoar frost.
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| 21. |
- Huang, Jianbin, et al.
(författare)
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The Amplified Arctic Warming in the Recent Decades may Have Been Overestimated by CMIP5 Models
- 2019
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 46:22, s. 13338-13345
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Tidskriftsartikel (refereegranskat)abstract
- ©2019. The Authors. Realistically representing the Arctic amplification in global climate models (GCMs) represents a key to accurately predict the climate system's response to increasing anthropogenic forcings. We examined the amplified Arctic warming over the past century simulated by 36 state-of-the-art GCMs against observation. We found a clear difference between the simulations and the observation in terms of the evolution of the secular warming rates. The observed rates of the secular Arctic warming increase from 0.14 °C/10a in the early 1890s to 0.21 °C/10a in the mid-2010s, while the GCMs show a negligible trend to 0.35 °C/10a at the corresponding times. The overestimation of the secular warming rate in the GCMs starts from the mid-twentieth century and aggravates with time. Further analysis indicates that the overestimation mainly comes from the exaggerated heating contribution from the Arctic sea ice melting. This result implies that the future secular Arctic warming may have been over-projected.
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| 22. |
- Kukulies, Julia, et al.
(författare)
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Mesoscale convective systems in the third pole region: Characteristics, mechanisms and impact on precipitation
- 2023
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Ingår i: Frontiers in Earth Science. - 2296-6463. ; 11
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Forskningsöversikt (refereegranskat)abstract
- The climate system of the Third Pole region, including the (TP) and its surroundings, is highly sensitive to global warming. Mesoscale convective systems (MCSs) are understood to be a vital component of this climate system. Driven by the monsoon circulation, surface heating, and large-scale and local moisture supply, they frequently occur during summer and mostly over the central and eastern TP as well as in the downstream regions. Further, MCSs have been highlighted as important contributors to total precipitation as they are efficient rain producers affecting water availability (seasonal precipitation) and potential flood risk (extreme precipitation) in the densely populated downstream regions. The availability of multi-decadal satellite observations and high-resolution climate model datasets has made it possible to study the role of MCSs in the under-observed TP water balance. However, the usage of different methods for MCS identification and the different focuses on specific subregions currently hamper a systematic and consistent assessment of the role played by MCSs and their impact on precipitation over the TP headwaters and its downstream regions. Here, we review observational and model studies of MCSs in the TP region within a common framework to elucidate their main characteristics, underlying mechanisms, and impact on seasonal and extreme precipitation. We also identify major knowledge gaps and provide suggestions on how these can be addressed using recently published high-resolution model datasets. Three important identified knowledge gaps are 1) the feedback of MCSs to other components of the TP climate system, 2) the impact of the changing climate on future MCS characteristics, and 3) the basin-scale assessment of flood and drought risks associated with changes in MCS frequency and intensity. A particularly promising tool to address these knowledge gaps are convection-permitting climate simulations. Therefore, the systematic evaluation of existing historical convection-permitting climate simulations over the TP is an urgent requirement for reliable future climate change assessments.
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| 23. |
- Lai, Hui-Wen, et al.
(författare)
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Regionalization of seasonal precipitation over the Tibetan plateau and associated large-scale atmospheric systems
- 2021
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 34:7, s. 2635-2651
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Tidskriftsartikel (refereegranskat)abstract
- Precipitation over the Tibetan Plateau (TP) has major societal impacts in South and East Asia, but its spatiotemporal variations are not well understood, mainly because of the sparsely distributed in situ observation sites. With the help of the Global Precipitation Measurement satellite product IMERG and the ERA5 dataset, distinct precipitation seasonality features over the TP were objectively classified using a self-organizing map algorithm fed with 10-day averaged precipitation from 2000 to 2019. The classification reveals three main precipitation regimes with distinct seasonality of precipitation: the winter peak, centered at the western plateau; the early summer peak, found on the eastern plateau; and the late summer peak, mainly located on the southwestern plateau. On a year-to-year basis, the winter peak regime is relatively robust, whereas the early summer and late summer peak regimes tend to shift mainly between the central and northern TP but are robust in the eastern and southwestern TP. A composite analysis shows that the winter peak regime experiences larger amounts of precipitation in winter and early spring when the westerly jet is anomalously strong to the north of the TP. Precipitation variations in the late summer peak regime are associated with intensity changes in the South Asian high and Indian summer monsoon. The precipitation in the early summer peak regime is correlated with the Indian summer monsoon together with anticyclonic circulation over the western North Pacific. The results provide a basic understanding of precipitation seasonality variations over the TP and associated large-scale conditions.
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| 24. |
- Lehsten, Veiko, et al.
(författare)
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Earlier occurrence and increased explanatory power of climate for the first incidence of potato late blight caused by Phytophthora infestans in Fennoscandia
- 2017
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- Background Late blight (caused by Phytophthora infestans) is a devastating potato disease that has been found to occur earlier in the season over the last decades in Fennoscandia. Up until now the reasons for this change have not been investigated. Possible explanations for this change are climate alterations, changes in potato production or changes in pathogen biology, such as increased fitness or changes in gene flow within P. infestans populations. The first incidence of late blight is of high economic importance since fungicidal applications should be typically applied two weeks before the first signs of late blight and are repeated on average once a week. We use field observations of first incidence of late blight in experimental potato fields from five sites in Sweden and Finland covering a total of 30 years and investigate whether the earlier incidence of late blight can be related to the climate. We linked the field data to meteorological data and found that the previous assumption, used in common late blight models, that the disease only develops at relative humidity levels above 90% had to be rejected. Rather than the typically assumed threshold relationship between late blight disease development and relative humidity we found a linear relationship. Our model furthermore showed two distinct responses of late blight to climate. At the beginning of the observation time (in Sweden until the early 90s and in Finland until the 2000s) the link between climate and first incidence was very weak. However, for the remainder of the time period the link was highly significant, indicating a change in the biological properties of the pathogen which could for example be a change in the dominating reproduction mode or a physiological change in the response of the pathogen to climate. The study shows that models used in decision support systems need to be checked and re parametrized regularly to be able to capture changes in pathogen biology. While this study was performed with data from Fennoscandia this new pathogen biology and late blight might spread to (or already be present at) other parts of the world as well. The strong link between climate and first incidence together with the presented model offers a tool to assess late blight incidence in future climates.
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| 25. |
- Lin, Changgui, 1985, et al.
(författare)
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A new perspective on solar dimming over the Tibetan Plateau
- 2019
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 39:1, s. 302-316
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 Royal Meteorological Society Solar radiation changes (dimming/brightening) have recently received growing attention within the research community, although there is currently no generally accepted explanation. This article aims to provide a new perspective for identifying the reasons behind solar dimming/brightening by using long-term measurements of direct and diffuse solar radiation, unlike previous studies which have focused on global solar radiation. We postulate that extinction processes can be more readily revealed by direct and diffuse radiation measurements with the help of a modelling tool that treats the two components separately. An example is presented for Golmud and Lhasa in the northern and southern Tibetan Plateau (TP) respectively, over the period 1957–2013. The following is found: (a) ground-based observed cloud cover alone hardly explains the observed solar dimming at the two sites; (b) both the cloud-free direct radiation transmittivity (τdir) and diffuse radiation proportion (pdif) declined; (c) variations in pdifare overwhelmingly dominated by variations in aerosols, while those in τdirare related to variations in both aerosol and water vapour; (d) on top of the suggested reduced aerosol concentrations, decreased snow cover can partly explain declined diffuse radiation via lowered surface albedo; (e) the decline in τdircan be partly attributed to the wetting atmosphere via strengthened absorption; and (f) the impact of volcanic eruptions was also identified from such radiative parameters, lasting into the following summer and especially strong in the southern TP.
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| 26. |
- Lin, Changgui, 1985, et al.
(författare)
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Impact of model resolution on simulating the water vapor transport through the central Himalayas: implication for models’ wet bias over the Tibetan Plateau
- 2018
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 51:9-10, s. 3195-3207
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 The Author(s) Current climate models commonly overestimate precipitation over the Tibetan Plateau (TP), which limits our understanding of past and future water balance in the region. Identifying sources of such models’ wet bias is therefore crucial. The Himalayas is considered a major pathway of water vapor transport (WVT) towards the TP. Their steep terrain, together with associated small-scale processes, cannot be resolved by coarse-resolution models, which may result in excessive WVT towards the TP. This paper, therefore, investigated the resolution dependency of simulated WVT through the central Himalayas and its further impact on precipitation bias over the TP. According to a summer monsoon season of simulations conducted using the weather research forecasting (WRF) model with resolutions of 30, 10, and 2 km, the study found that finer resolutions (especially 2 km) diminish the positive precipitation bias over the TP. The higher-resolution simulations produce more precipitation over the southern Himalayan slopes and weaker WVT towards the TP, explaining the reduced wet bias. The decreased WVT is reflected mostly in the weakened wind speed, which is due to the fact that the high resolution can improve resolving orographic drag over a complex terrain and other processes associated with heterogeneous surface forcing. A significant difference was particularly found when the model resolution is changed from 30 to 10 km, suggesting that a resolution of approximately 10 km represents a good compromise between a more spatially detailed simulation of WVT and computational cost for a domain covering the whole TP.
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| 27. |
- Lin, Changgui, 1985, et al.
(författare)
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Summer afternoon precipitation associated with wind convergence near the Himalayan glacier fronts
- 2021
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Ingår i: Atmospheric Research. - : Elsevier BV. - 0169-8095. ; 259
-
Tidskriftsartikel (refereegranskat)abstract
- Little is known about the effects of glacier-air interactions on the Himalayan glacier mass balance. Until this knowledge gap is filled, a reliable projection of the future changes in the Himalayan glaciers is hardly possible. Here, we describe the drying effect of the katabatic winds on the up-valley summer monsoon flows by creating favorable conditions for local convergence-induced precipitation to occur near the glacier fronts. We postulate that this retarding effect on the up-valley monsoon flows results in a negative feedback mechanism mediated by glacier-air interactions, in which glacial retreat pushes precipitation upwards as the down-valley katabatic winds weaken, resulting in greater local precipitation and enhanced snow accumulation across the upper parts of the Himalayan glaciers. Our analyses are based on the exclusive data recorded in the Khumbu valley and the Langtang valley in the Nepalese Himalayas. These data revealed higher afternoon precipitation in summer associated with surface wind convergence near the glacier fronts and a sharp decrease in the temperature lapse rate over the glacier surfaces. The principle of the observed phenomena was proven by our high-resolution modeling sensitive experiment, which involved two simulations, one with the present glaciers and the other without. This numerical experiment also supports the proposed negative feedback. Furthermore, we report a low deuterium excess near the glacier fronts, indicating below-cloud re-evaporation facilitated by the local convergence induced by the dry katabatic winds. Our study suggests that current models may overestimate the retreat of Himalayan glaciers because they have completely ignored the glacier-air interactions. © 2021 The Author(s)
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| 28. |
- Lin, Q., et al.
(författare)
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Performance of the WRF Model at the Convection-Permitting Scale in Simulating Snowfall and Lake-Effect Snow Over the Tibetan Plateau
- 2023
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Ingår i: Journal of Geophysical Research-Atmospheres. - 2169-897X. ; 128:16
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigated the performance of the Weather Research Forecasting (WRF) model at 4-km horizontal grid spacing in simulating precipitation, 2 m air temperature (T2), snowfall, and lake-effect snow (October 4-8, 2018) over the Tibetan Plateau (TP). Multiple simulations with different physical parameterization schemes (PPSs), including two planetary boundary layer schemes (Yonsei University and Mellor-Yamada-Janjic), no cumulus and multi-scale Kain-Fritsch, two land surface models (Noah and Noah-MP), and two microphysics schemes (Thompson and Milbrandt), were conducted and compared. Compared with gauge observations, all PPSs simulate mean daily precipitation with mean relative errors (MREs) of 27.7%-53.6%. Besides, spatial correlation coefficients (SCCs) between simulated and observed mean daily precipitation range from 0.56 to 0.71. For simulations of T2, all PPSs perform similarly well, even though the mean cold biases are up to about 3 degrees C. Meanwhile, all PPSs exhibit acceptable performance in simulating spatial distributions of snow depth, snow cover, and snowfall amount, with SCCs of 0.37-0.65 between simulations and observations. However, the WRF simulations significantly overestimate snow depth (similar to 0.4 cm mean error) and snowfall amount (MREs >372%). The Milbrandt scheme slightly outperforms the other PPSs in simulating snow-related variable magnitudes. Due to their inaccurate temperature and airflow modeling over the lake surface and its surroundings, none of the WRF simulations well reproduce the characteristics that more snow occurs over the lake and downwind area. Overall, this study provides a useful reference for future convection-permitting climate modeling of snow or other extreme events when using the WRF model in the TP and other alpine regions. Plain Language Summary Snow falls frequently in cold seasons, especially in alpine regions. When there is a lake, a very interesting snowfall phenomenon named lake-effect snow may happen, that is, more snow occurred over the lake and downwind areas. However, the lake-effect snow caused by large lakes over the Tibetan Plateau (TP) may induce snow disaster events. Thus, conducting reliable simulations of lake-effect snow events are essential for understanding the mechanism of these particular events over the TP. This study investigated the performance of the numerical model in simulating precipitation, 2 m air temperature (T2), snowfall, and lake-effect snow (October 4-8, 2018) over the TP. The results show that the simulated precipitation and T2 perform reasonably well, although wet and cold biases are observed. However, the investigated numerical model fails to reproduce the characteristics of this event well, which may be due to the inaccurate temperature and airflow modeling over the lake surface and its surroundings. Continued improvement is needed for future modeling. Hence, this study provides some suggestions for future numerical modeling of lake-effect snow or other snow events over the TP and other alpine regions.
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| 29. |
- Linderholm, Hans W., 1968, et al.
(författare)
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Exploring teleconnections between the summer NAO (SNAO) and climate in East Asia over the last four centuries – a tree-ring perspective
- 2013
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Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865. ; 31:4, s. 297-310
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Tidskriftsartikel (refereegranskat)abstract
- The summer North Atlantic Oscillation (SNAO), derived from the first EOF of mean sea level pressure over the extratropical North Atlantic in July and August, has a close association with climate variability over the North Atlantic region, and beyond, on both short and long time scales. Recent findings suggested a teleconnection, through the SNAO, linking climate variability over Northern Europe with that of East Asia in the latter part of the twentieth century. Here we investigate the temporal stability of that teleconnection for the last four centuries using 4261 tree-ring width series from 106 sites and, additionally, ten climate reconstructions from East Asia. Our results showed a great potential in using tree-ring width (TRW) data to extend analyses of the SNAO influence on East Asian climate beyond the instrumental period, but preferably with a denser network. The strongest SNAO-TRW associations were found in central East Asia (in and around Mongolia) and on the eastern edge of the Tibetan Plateau. In addition, the analysis showed that the association between the SNAO and East Asian climate over the last 400 years has been variable, both among regions and at specific sites. Moreover, a clear difference in the SNAO-TRW associations was found on two examined time scales, being stronger on longer timescales. Our results indicate that TRW data can be a useful tool to explore the remote influence of the SNAO on East Asian climate in the past.
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| 30. |
- Linderholm, Hans W., 1968, et al.
(författare)
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Influences of large- and regional-scale climate on fish recruitment in the Skagerrak-Kattegat over the last century
- 2014
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963. ; 134, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Dynamics of commercial fish stocks are generally associated with fishing pressure and climate variability. Due to short time series, past studies of the relationships between fish stock dynamics and climate have mainly been restricted to the last few decades. Here we analyzed a century-long time series of plaice, cod and haddock from the Skagerrak-Kattegat, to assess the long-term influence of climate on recruitment. Recruitment success (R-s) was compared against sea-surface temperature (SST) and atmospheric circulation indices on large (North Atlantic) and regional (Skagerrak-Kattegat) scales. Our results show that the influence of climate on R-s was more pronounced on longer, than on shorter timescales. Over the century-long period, a shift from low to high climate sensitivity was seen from the early to the late part for plaice and cod, while the opposite was found for haddock. This shift suggests that the increasing fishing pressure and the climate change in the Skagerrak-Kattegat have resulted in an increased sensitivity of R-s to climate for plaice and cod. The diminishing of climate sensitivity in haddock R-s, on the other hand, may be linked to the early twentieth century collapse of the stock in the region. While no long-term relationship between R-s and the Atlantic Multidecadal Oscillation (AMO) could be found, large R-s fluctuations during the positive phase of the AMO (1935-1960), relative to the cold phases, suggests a changed pattern in recruitment during warm periods. On the other hand, this could be due to the increased fishing pressure in the area. Thus, reported correlations between climate and fish may be caused by strong trends in climate in the late-twentieth century, and coincident reduction in fish stocks caused by intense fishing, rather than a stable relationship between climate and fish recruitment per se. (C) 2014 Elsevier B.V. All rights reserved.
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| 31. |
- Linderholm, Hans W., 1968, et al.
(författare)
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Interannual teleconnections between the summer North Atlantic Oscillation and the East Asian summer monsoon
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116:D13
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Tidskriftsartikel (refereegranskat)abstract
- Here we present a study of the relationship between July–August (JA) mean climate over China, which is strongly linked to the East Asian summer monsoon (EASM), and the summer (JA) North Atlantic Oscillation (SNAO). The variations of temperature, precipitation, and cloud cover related to the SNAO were analyzed for the period 1951–2002 using gridded data sets as well as instrumental data from 160 stations in China. It was shown that the major patterns of summer climate over China are highly connected with the interannual variation of the SNAO, supporting a teleconnection between the North Atlantic region and East Asia. Based on the analyses of the daily and monthly reanalysis data sets, we propose possible mechanisms of this teleconnection. Changes in the position of the North Atlantic storm tracks and transient eddy activity associated with the positive (negative) SNAO phase contribute downstream to negative (positive) sea level pressure anomalies in northeastern East Asia. In negative SNAO years, a stationary wave pattern is excited from the southern SNAO center over northwestern Europe to northeastern East Asia. However, during positive SNAO years, a stationary wave pattern is excited extending from the SNAO center across the central Eurasian continent at around 40°N and downstream to the southeast. This may explain a connection between the positive SNAO and atmospheric circulation in middle and southeastern China.
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| 32. |
- Ma, Mengnan, et al.
(författare)
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Contribution of Recycled and External Advected Moisture to Precipitation and Its Inter-Annual Variation Over the Tibetan Plateau
- 2024
-
Ingår i: Journal of Geophysical Research: Atmospheres. - 2169-897X .- 2169-8996. ; 129
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we performed a high-resolution simulation using the Weather Research and Forecasting model, integrated with water vapor tracers, covering the years 2005–2019. Our objective was to obtain deeper insights into the spatiotemporal dynamics of external advected and local evaporative water vapor, and to elucidate their impact on precipitation patterns across the Tibetan Plateau (TP). Our findings underscore that a significant proportion of TP's precipitation originates from external advected water vapor, primarily entering through the western and southern boundaries. During summer, stronger zonal and meridional water vapor transport, driven by prevailing westerly winds and the Asian monsoon, significantly influences seasonal and spatial precipitation variations. Additionally, we observed that the inter-annual variation of precipitation is intricately linked to changes in the net water vapor influx, modulated by alterations in atmospheric circulation. We also analyze the Precipitation Recycling Ratio (PRR) which refers to the proportion of precipitation originated from local evaporative water vapor to the total precipitation, revealing distinctive elevation-dependent variations aligned with grassland distribution. Notably, PRR exhibits asynchronous shifts with precipitation at different timescales, potentially linked to soil moisture-precipitation feedback at intra-annual scales. Moreover, the investigation highlights that inter-annual variations in PRR are primarily linked to the inflow and outflow of water vapor as well as wind strength at 500hPa, particularly prominent during colder seasons, while thermal factors carry comparable weight to dynamical factors in warmer seasons.
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| 33. |
- Ma, Mengnan, et al.
(författare)
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High-resolution climate projection over the Tibetan Plateau using WRF forced by bias-corrected CESM
- 2023
-
Ingår i: Atmospheric Research. - : Elsevier BV. - 0169-8095. ; 286
-
Tidskriftsartikel (refereegranskat)abstract
- The Tibetan Plateau (TP) has undergone significant climate warming with a stronger amplitude than that experienced elsewhere in the Northern Hemisphere during the past years, but it is still challenging for most regional climate models to realistically simulate the present-day climate and promisingly project the future climate over the TP. In this study, high-resolution simulation using the Weather Research and Forecasting model (WRF) driven by bias-corrected CESM is conducted from 1979 to 2100, with the period from 2006 to 2100 under RCP4.5 and RCP8.5 (Representative Concentration Pathways) scenarios. The simulated present-day climate is evaluated firstly and then the future climate is studied secondly. The results show that compared with station observation, WRF successfully captures the spatial pattern of annual mean surface air temperature (T2m) and precipitation over the TP, with the spatial correlation coefficients larger than 0.95 for T2m and larger than 0.70 for precipitation. However, great underestimation of T2m over the southeastern TP is found in the cold season which is related to the underestimation of snow there, and the snow-temperature positive feedback develops. WRF shows limited ability in reducing the dry bias in summer, which is related to the simulated weaker water vapor transport over the southern and eastern TP. For the future changes, substantial warming, general increase in precipitation and decrease in snow are projected under RCP8.5. The warming magnitude is greater over the western TP where the more significant decrease of snow will occur by the end of 21st century. Projected precipitation tends to consistently decrease over the western TP and along the south flank of TP which is related to the low-level circulation change. The occurring frequency of light precipitation will decrease while that of non-precipitation and extreme precipitation will increase especially in the far future, with the more obvious change occurring under RCP8.5. Overall, WRF shows high ability in simulating the present-day climate and thus reliable performance in future climate projection.
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| 34. |
- Ma, Mengnan, et al.
(författare)
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Subdaily Extreme Precipitation and Its Linkage to Global Warming Over the Tibetan Plateau
- 2023
-
Ingår i: Journal of Geophysical Research: Atmospheres. - 2169-897X .- 2169-8996. ; 128:18
-
Tidskriftsartikel (refereegranskat)abstract
- The spatiotemporal characteristics of subdaily extreme precipitation over the Tibetan Plateau (TP) have undergone significant changes due to global warming. In this study, we employed the high-resolution Weather Research and Forecasting regional climate model to conduct a series of historical and projection simulations under representative concentration pathways (RCPs), especially RCP4.5 and RCP8.5. The aim was to investigate the past and future climatologies and spatiotemporal evolution of subdaily precipitation extremes using newly proposed subdaily extreme precipitation indices (EPIs). The results show that projected changes in precipitation amount, particularly during wet hours, exhibit spatial disparaties. Notably, there are significant decreases along the southern border of the TP and over the western TP, while obvious increases are observed over the inner TP. The southeastern TP, western TP, and southern border of the TP are expected to experience less frequent, shorter duration, and more intense precipitation on an hourly basis. The TP, as a whole, has demonstrated significantly increasing trends in moderate-to-heavy precipitation frequencies, along with consistent decreasing trends in precipitation events with short, medium, and long durations. Furthermore, it is predicted that the relationship between extreme precipitation and temperature will deviate from the Clausius-Clapeyron (C-C) relationship toward the double C-C relationship in the far-future under RCP8.5, particularly over the southeastern TP. Additionally, there are robust correlations between the intensity-related EPIs and elevation. This indicates that, at the local scale, the complex topography of the region may play a crucial role in shaping the nonuniform distribution of precipitation extremes by modulating associated upward motion.
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| 35. |
- Ma, Mengnan, et al.
(författare)
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Summer regional climate simulations over Tibetan Plateau: from gray zone to convection permitting scale
- 2022
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894.
-
Tidskriftsartikel (refereegranskat)abstract
- The Tibetan Plateau (TP) is often referred to as ‘the Third Pole’ and plays an essential role in the global climate. However, it remains challenging for most global and regional models to realistically simulate the characteristics of climate over the TP. In this study, two Weather Research and Forecasting model (WRF) experiments using spectral nudging with gray-zone (GZ9) and convection-permitting (CP3) resolution are conducted for summers from 2009 to 2018. The surface air temperature (T2m) and precipitation from the two simulations and the global reanalysis ERA5 are evaluated against in-situ observations. The results show that ERA5 has a general cold bias over southern TP, especially in maximum T2m (Tmax), and wet bias over whole TP. Both experiments can successfully capture the spatial pattern and daily variation of T2m and precipitation, though cold bias for temperature and dry bias for precipitation exist especially over the regions south of 35° N. Compared with ERA5, the added value of the two WRF experiments is mainly reflected in the reduced cold bias especially for Tmax with more improvement found in CP3 and the reduced wet bias. However, the ability of the convection-permitting WRF experiment in improving the simulation of precipitation seems limited when compared to the gray-zone WRF experiment, which may be related to the biases in physical parameterization and lack of representativeness of station observation. Further investigation into surface radiation budget reveals that the underestimation of net shortwave radiation contributes a lot to the cold bias of T2m over the southeastern TP in GZ9 which is improved in CP3. Compared with GZ9, CP3 shows that larger specific humidity at low-level (mid-high level) coexists with more precipitation (clouds) over the southern TP. This improvement is achieved by better depiction of topographic details, underlying surface and atmospheric processes, land–atmosphere interactions and so on, leading to stronger northward water vapor transport (WVT) in CP3, providing more water vapor for precipitation at surface and much wetter condition in the mid-high level.
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| 36. |
- Minola, Lorenzo, et al.
(författare)
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Climatology of near-surface wind speed from observational, reanalysis and high-resolution regional climate model data over the Tibetan Plateau
- 2023
-
Ingår i: Climate Dynamics. - 0930-7575 .- 1432-0894.
-
Tidskriftsartikel (refereegranskat)abstract
- As near-surface wind speed plays a role in regulating surface evaporation and thus the hydrological cycle, it is crucial to explore its spatio-temporal characteristics. However, in-situ measurements are scarce over the Tibetan Plateau, limiting the understanding of wind speed climate across this high-elevation region. This study explores the climatology of near-surface wind speed over the Tibetan Plateau by using for the first time homogenized observations together with reanalysis products and regional climate model simulations. Measuring stations across the center and the west of the plateau are at higher elevations and display higher mean and standard deviation, confirming that wind speed increases with increasing altitude. By exploring wind characteristics with a focus on seasonal cycle through cluster analysis, three regions of distinct wind regimes can be identified: (1) the central Tibetan Plateau, characterized by high elevation; (2) the eastern and the peripheral areas of the plateau; and (3) the Qaidam basin, a topographic depression strongly influenced by the blocking effect of the surrounding mountainous terrain. Notably, the ERA5 reanalysis, with its improvements in horizontal, vertical, and temporal spacing, model physics and data assimilation, demonstrates closer agreement to the measured wind conditions than its predecessor ERA-Interim. It successfully reproduces the three identified wind regimes. However, the newest ERA5-Land product does not show improvements compared to ERA5, most likely because they share most of the parametrizations. Furthermore, the two dynamical downscalings of ERA5 analyzed here fail to capture the observed wind statistics and exhibit notable biases and discrepancies also when investigating the diurnal variations. Consequently, these high-resolution downscaling products do not show add value in reproducing the observed climatology of wind speed compared to ERA5 over the Tibetan Plateau.
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| 37. |
- Niu, X. R., et al.
(författare)
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Elevation-Dependent Warming Over the Tibetan Plateau From an Ensemble of CORDEX-EA Regional Climate Simulations
- 2021
-
Ingår i: Journal of Geophysical Research-Atmospheres. - : American Geophysical Union (AGU). - 2169-897X .- 2169-8996. ; 126:9
-
Tidskriftsartikel (refereegranskat)abstract
- Under the Coordinated Regional Climate Downscaling Experiments-East Asia (CORDEX-EA-II), the outputs from two regional climate models (RCMs) driven by four global climate models (GCMs) are used to investigate the characteristics and possible mechanisms of the projected elevation-dependent warming (EDW) over the Tibetan Plateau (TP) under the Representative Concentration Pathway emission scenario 8.5 (RCP8.5). Results show that widespread warming over the TP is projected with considerable disagreements in warming intensity and the maximum warming center among RCMs. The largest spread in the surface air temperature (T-as) projections is found above 5,000 m, indicating that a large uncertainty exists over the higher elevations. A marked EDW signal over the TP is simulated under the RCP 8.5 by the multi-RCM ensemble mean for all seasons, particularly in autumn. Based on the analysis of the surface energy budget, it is found that the surface albedo feedback (SAF) is the primary contributor to EDW and acts as the main source of uncertainty in EDW projections among RCMs. The downward longwave radiation (DLW) is found to be the dominant factor in regulating T-as change over the TP, and its contribution to EDW is model-dependent. Furthermore, the structure and magnitude of projected EDW are sensitive to the RCM physics and driving GCM, as they can alter the projections of snow cover and albedo, which modulate the simulated SAF and its effect on EDW. Additionally, RegCM4 shows a higher sensitivity to the anthropogenic greenhouse forcing than WRF, evidenced by the larger temperature projections and stronger EDW signal in RegCM4.
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| 38. |
- Niu, Xiaorui, et al.
(författare)
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The performance of CORDEX-EA-II simulations in simulating seasonal temperature and elevation-dependent warming over the Tibetan Plateau
- 2021
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 57, s. 1135-1153
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Tidskriftsartikel (refereegranskat)abstract
- To explore the driving mechanisms of elevation-dependent warming (EDW) over the Tibetan Plateau (TP), the output from a suite of numerical experiments with different cumulus parameterization schemes (CPs) under the Coordinated Regional Climate Downscaling Experiments-East Asia (CORDEX-EA-II) project is examined. Results show that all experiments can broadly capture the observed temperature distributions over the TP with consistent cold biases, and the spread in temperature simulations commonly increases with elevation with the maximum located around 4000-5000 m. Such disagreements among the temperature simulations could to a large extent be explained by their spreads in the surface albedo feedback (SAF). All the experiments reproduce the observed EDW below 5000 m in winter but fail to capture the observed EDW above 4500 m in spring. Further analysis suggests that the simulated EDW during winter is mainly caused by the SAF, and the clear-sky downward longwave radiation (LWclr) plays a secondary role in shaping EDW. The models' inability in simulating EDW during spring is closely related to the SAF and the surface cloud radiative forcing (CRFs). Furthermore, the magnitude and structure of the simulated EDW are sensitive to the choice of CPs. Different CPs generate diverse snow cover fractions, which can modulate the simulated SAF and its effect on EDW. Also, the CPs show great influence on the LWclr via altering the low-level air temperature. Additionally, the mechanism for different temperature changes among the experiments varies with altitudes during summer and autumn, as the diverse temperature changes appear to be caused by the LWclr for the low altitudes while by the SAF for the middle-high altitudes.
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| 39. |
- Ou, Tinghai, et al.
(författare)
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Changes in winter cold surges over Southeast China: 1961 to 2012
- 2015
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Ingår i: Asia-Pacific Journal of Atmospheric Sciences. - : Springer Science and Business Media LLC. - 1976-7633 .- 1976-7951. ; 51:1, s. 29-37
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigates the overall changes in occurrences of winter cold surges over Southeast China for the period 1961-2012, using instrumental observations, reanalysis and model simulation datasets. Based on objectively defined criteria, cold surges were classified into 3 types according to their dynamical origin as inferred from daily evolution patterns of surface pressure systems with a focus on the Siberian High (SH): type A with an amplification of a quasi-stationary SH associated with high-pressure anomalies over the Ural mountains, type B with a developing SH associated with fast traveling upper-level waves, and type C with a high-pressure originated in the Arctic. Examination of the long-term change in cold surge occurrences shows different interdecadal variations among the 3 types. During 1961-2012, type A events (37.8%) decreased, while type B events, accounting for the majority (52.5%) of total winter cold surges, increased slightly. The contribution by type C to the total occurrence of the cold surges was small (8.8%) compared to that of A and B, but it became more frequent in the latest decade, related to the tendency of the Arctic Oscillation (AO) being more in its negative phase. Overall, we found slightly increased occurrences of cold surges over Southeast China since the early 1980s, despite the weakened SH intensity and warmer mean temperature compared to previous decades. The climate model projections of the phase 5 of the Coupled Model Intercomparison Project (CMIP5) suggests similar trend in the late 21st century under warmer climate.
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| 40. |
- Ou, Tinghai, et al.
(författare)
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Evaluation of global climate models in simulating extreme precipitation in China
- 2013
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Ingår i: Tellus. Series A, Dynamic meteorology and oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 65
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Tidskriftsartikel (refereegranskat)abstract
- Variations in extreme precipitation can be described by various indices. In order to evaluate a climate model’s ability to simulate extreme precipitation, gridded extreme precipitation indices from observations are needed. There are two ways to obtain gridded extreme precipitation indices from station-based observations: either through interpolation of station-based extreme indices (EISTA) or estimated from gridded precipitation datasets (EIGRID). In this work, we evaluated these two methods and compared observational extreme precipitation indices in China to those obtained from a set of widely used global climate models. Results show that the difference between the two methods is quite large; and in some cases it is even larger than the difference between model simulations and observed gridded EISTA. Based on the sensitivity of the indices to horizontal resolution, it was suggested that EIGRID is more appropriate for evaluating extreme indices simulated by models. Subsequently, historic simulations of extreme precipitation from 21 CMIP5 (Coupled Model Intercomparison Project Phase 5) global climate models were evaluated against two reanalysis datasets during 1961-2000. It was found that most models overestimate extreme precipitation in the mountain regions in western China and northern China and underestimate extreme precipitation in southern China. In eastern China, these models simulate mean extreme precipitation fairly well. Despite this bias, the temporal trend in extreme precipitation for western China is well captured by most models. However, in eastern China, the trend of extreme precipitation is poorly captured by most models, especially for the so-called southern flood and northern drought pattern. Overall, our results suggest that the dynamics of inter-decadal summer monsoon variability should be improved for better prediction of extreme precipitation by the global climate models
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| 41. |
- Ou, Tinghai
(författare)
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Observed and simulated changes in extreme precipitation and cold surges in China: 1961–2005
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the present work, precipitation and temperature related climate extremes are examined, with a focus on Mainland China. The objectives of this study are a) to identify targeted climate extremes and their changes during the last decades, and b) to examine the ability of current global climate models to reproduce identified patterns of change. The observed change in extreme precipitation from 1961 to 2000 is investigated using a set of indices, and the change simulated by global climate models is evaluated. In order to find an appropriate gridding method for the extreme indices in model evaluations, the effects of two different methods for estimating indices from station data are examined: one set interpolated from indices at stations (EISTA) and the other calculated from gridded precipitation (EIGRID). Results show that there is a large difference between the two, especially at coarser resolution, and suggests that EIGRID indices are more appropriate to evaluate model simulated precipitation extremes. During the period in question, observed extreme precipitation amounts increased in most parts of China, the only exception being northern China, where there was a decreasing trend. The trend of consecutive dry days (CDD) observed there is generally opposite to that of extreme precipitation elsewhere in China, except in southeast China, where both extreme precipitation and CDD increased. Most of the studied global climate models tend to overestimate extreme precipitation amounts but underestimate CDD. The pattern of precipitation extremes is generally well captured in western China, while in eastern China, where the combination of the monsoon system and human activities (e.g., anthropogenic changes in land use and aerosols) affects climate variation, with the result that climate patterns are reproduced poorly by comparison. In regard to temperature-related extremes, the variation in the occurrence of winter cold surges in southeast China for the period from 1961 to 2005 is investigated. The identified cold surges are divided into 5 different groups based on the evolution pattern of the Siberian High (SH). Associated evolutions of the large-scale atmospheric circulation are investigated. Results suggest the importance of a SH amplification and pre-existing specific synoptic systems to the occurrence of cold surges. Investigating the long-term changes in cold surges of different groups, it is found that the SH-related cold surges (33%) have decreased in the last 20 years, while cold surges more closely associated with background atmospheric circulation systems, which often have a larger impact area (i.e., stronger cold air outbreak) than the SH-related ones, have increased since the early 1980s. Although the intensity of SH was relatively weak with warmer surface air temperatures over China during the period from 1980 to 2005, the total number of cold surges in this period was nearly identical to that of previous decades. This implies that future occurrences of cold surges in southeast China may remain at current levels, provided that the contribution from the SH-related surges does not change dramatically.
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| 42. |
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| 43. |
- Ou, Tinghai, et al.
(författare)
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Simulation of summer precipitation diurnal cycles over the Tibetan Plateau at the gray-zone grid spacing for cumulus parameterization
- 2020
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 54, s. 3525-3539
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Tidskriftsartikel (refereegranskat)abstract
- The Tibetan Plateau (TP) is often referred to as the “water tower of Asia” or the “Third Pole”. It remains a challenge for most global and regional models to realistically simulate precipitation, especially its diurnal cycles, over the TP. This study focuses on evaluating the summer (June–August) precipitation diurnal cycles over the TP simulated by the Weather Research and Forecasting (WRF) model. The horizontal resolution used in this study is 9 km, which is within the gray-zone grid spacing that a cumulus parameterization scheme (CU) may or may not be used. We conducted WRF simulations with different cumulus schemes (CU experiments) and a simulation without CU (No_CU experiment). The selected CUs include the Grell-3D Ensemble (Grell), New Simplified Arakawa-Schubert (NSAS), and Multiscale Kain-Fritsch (MSKF). These simulations are compared with both the in-situ observations and satellite products. Results show that the scale-aware MSKF outperforms the other CUs in simulating precipitation in terms of both the mean intensity and diurnal cycles. In addition, the peak time of precipitation intensity is better captured by all the CU experiments than by the No_CU experiment. However, all the CU experiments tend to overestimate the mean precipitation and simulate an earlier peak of precipitation frequency when compared to observations. The frequencies and initiation timings for short-duration (1–3 h) and long-duration (> 6 h) precipitation events are well captured by the No_CU experiment, while these features are poorly reproduced by the CU experiments. The results demonstrate simulation without a CU outperforms those with a CU at the gray-zone spatial resolution in regard to the precipitation diurnal cycles.
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| 44. |
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| 45. |
- Ou, Tinghai, et al.
(författare)
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Wet bias of summer precipitation in the northwestern Tibetan Plateau in ERA5 is linked to overestimated lower-level southerly wind over the plateau
- 2023
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 61:5-6, s. 2139-53
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Tidskriftsartikel (refereegranskat)abstract
- The Tibetan Plateau (TP), also called the Third Pole, is considered to be “the world water tower”. The northwestern TP (NWTP), which has an average elevation higher than 4800m, is an arid region where the summer precipitation is largely overestimated by the ERA5 global reanalysis product. We hypothesize that this wet bias is mainly caused by unrealistic lower-level winds that trigger strong convection over the region; it can be reduced by using a high-resolution regional climate model with a large domain that allows realistically representing interactions between the Westerlies and Asian summer monsoons. Here, downscaling using the Weather Research and Forecasting (WRF) model driven by ERA5 was conducted with a large domain (8°‒50° N, 65°‒125° E) at 9km for the period 1979‒2019 (WRF9km). Precipitation values from WRF9km and ERA5 were evaluated against satellite observations; compared with ERA5, WRF9km captured the climatological summer precipitation over the NWTP with a much-reduced wet bias. The ERA5 overestimation is mainly caused by excessive convective precipitation, likely linked to strong vertical motions over the NWTP induced by an overestimated lower-level southerly wind.
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| 46. |
- Prein, Andreas F., et al.
(författare)
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Towards Ensemble-Based Kilometer-Scale Climate Simulations over the Third Pole Region
- 2022
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894.
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Tidskriftsartikel (refereegranskat)abstract
- The Tibetan Plateau and its surrounding mountains have an average elevation of 4,400m and a glaciated area of ∼ 100,000km 2 giving it the name “Third Pole (TP) region”. The TP is the headwater of many major rivers in Asia that provide fresh water to hundreds of millions of people. Climate change is altering the energy and water cycle of the TP at a record pace but the future of this region is highly uncertain due to major challenges in simulating weather and climate processes in this complex area. The Convection-Permitting Third Pole (CPTP) project is a Coordinated Regional Downscaling Experiment (CORDEX) Flagship Pilot Study (FPS) that aims to revolutionize our understanding of climate change impacts on the TP through ensemble-based, kilometer-scale climate modeling. Here we present the experimental design and first results from multi-model, multi-physics ensemble simulations of three case studies. The five participating modeling systems show high performance across a range of meteorological situations and are close to having ”observational quality” in simulating precipitation and near-surface temperature. This is partly due to the large differences between observational datasets in this region, which are the leading source of uncertainty in model evaluations. However, a systematic cold bias above 2000m exists in most modeling systems. Model physics sensitivity tests performed with the Weather Research and Forecasting (WRF) model show that planetary boundary layer (PBL) physics and microphysics contribute equally to model uncertainties. Additionally, larger domains result in better model performance. We conclude by describing high-priority research needs and the next steps in the CPTP project.
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| 47. |
- Shaw, T. E., et al.
(författare)
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Multi-decadal monsoon characteristics and glacier response in High Mountain Asia
- 2022
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 17:10
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Tidskriftsartikel (refereegranskat)abstract
- Glacier health across High Mountain Asia (HMA) is highly heterogeneous and strongly governed by regional climate, which is variably influenced by monsoon dynamics and the westerlies. We explore four decades of glacier energy and mass balance at three climatically distinct sites across HMA by utilising a detailed land surface model driven by bias-corrected Weather Research and Forecasting meteorological forcing. All three glaciers have experienced long-term mass losses (ranging from -0.04 +/- 0.09 to -0.59 +/- 0.20 m w.e. a(-1)) consistent with widespread warming across the region. However, complex and contrasting responses of glacier energy and mass balance to the patterns of the Indian Summer Monsoon were evident, largely driven by the role snowfall timing, amount and phase. A later monsoon onset generates less total snowfall to the glacier in the southeastern Tibetan Plateau during May-June, augmenting net shortwave radiation and affecting annual mass balance (-0.5 m w.e. on average compared to early onset years). Conversely, timing of the monsoon's arrival has limited impact for the Nepalese Himalaya which is more strongly governed by the temperature and snowfall amount during the core monsoon season. In the arid central Tibetan Plateau, a later monsoon arrival results in a 40 mm (58%) increase of May-June snowfall on average compared to early onset years, likely driven by the greater interaction of westerly storm events. Meanwhile, a late monsoon cessation at this site sees an average 200 mm (192%) increase in late summer precipitation due to monsoonal storms. A trend towards weaker intensity monsoon conditions in recent decades, combined with long-term warming patterns, has produced predominantly negative glacier mass balances for all sites (up to 1 m w.e. more mass loss in the Nepalese Himalaya compared to strong monsoon intensity years) but sub-regional variability in monsoon timing can additionally complicate this response.
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| 48. |
- Su, F., et al.
(författare)
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Contrasting Fate of Western Third Pole's Water Resources Under 21st Century Climate Change
- 2022
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Ingår i: Earth's Future. - 2328-4277. ; 10:9
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Tidskriftsartikel (refereegranskat)abstract
- Seasonal melting of glaciers and snow from the western Third Pole (TP) plays important role in sustaining water supplies downstream. However, the future water availability of the region, and even today's runoff regime, are both hotly debated and inadequately quantified. Here, we characterize the contemporary flow regimes and systematically assess the future evolution of total water availability, seasonal shifts, and dry and wet discharge extremes in four most meltwater-dominated basins in the western TP, by using a process-based, well-established glacier-hydrology model, well-constrained historical reference climate data, and the ensemble of 22 global climate models with an advanced statistical downscaling and bias correction technique. We show that these basins face sharply diverging water futures under 21st century climate change. In RCP scenarios 4.5 and 8.5, increased precipitation and glacier runoff in the Upper Indus and Yarkant basins more than compensate for decreased winter snow accumulation, boosting annual and summer water availability through the end of the century. In contrast, the Amu and Syr Darya basins will become more reliant on rainfall runoff as glacier ice and seasonal snow decline. Syr Darya summer river-flows, already low, will fall by 16%–30% by end-of-century, and striking increases in peak flood discharge (by >60%), drought duration (by >1 month) and drought intensity (by factor 4.6) will compound the considerable water-sharing challenges on this major transboundary river.
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| 49. |
- Su, F., et al.
(författare)
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Hydrological response to future climate changes for the major upstream river basins in the Tibetan Plateau
- 2016
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 136, s. 82-95
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Tidskriftsartikel (refereegranskat)abstract
- The impacts of future climate change on water balance for the headwater basins of six major rivers in the Tibetan Plateau are assessed using the well-established VIC-glacier land surface hydrological model driven by composite projections of 20 CMIP5 GCMs under scenarios RCP2.6, RCP4.5, and RCP8.5. At the plateau scale, the annual precipitation is projected to increase by 5.0–10.0% in the near term (2011–2040) and 10.0–20.0% in the long term (2041–2070) relative to the reference period 1971–2000. The annual temperature is projected to increase for all the scenarios with the greatest warming in the northwest (2.0–4.0 °C) and least in the southeast (1.2–2.8 °C). The total runoff of the study basins would either remain stable or moderately increase in the near term, and increase by 2.7–22.4% in the long term relative to the reference period, as a result of increased rainfall-induced runoff for the upstream of the Yellow, Yangtze, Salween, and Mekong and increased glacier melt for the upper Indus. In the upper Brahmaputra, more than 50.0% of the total runoff increase is attributed to the increased glacier melt in the long run. The annual hydrograph remains practically unchanged for all the monsoon-dominated basins. However, for the westerly-controlled basin (upper Indus), an apparent earlier melt and a relatively large increase in spring runoff are observed for all the scenarios, which would increase water availability in the Indus Basin irrigation scheme during the spring growing season.
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| 50. |
- Sun, H., et al.
(författare)
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Corrected ERA5 Precipitation by Machine Learning Significantly Improved Flow Simulations for the Third Pole Basins
- 2022
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Ingår i: Journal of Hydrometeorology. - : American Meteorological Society. - 1525-755X .- 1525-7541. ; 23:10, s. 1663-1679
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Tidskriftsartikel (refereegranskat)abstract
- Precipitation is one of the most important atmospheric inputs to hydrological models. However, existing precipitation datasets for the Third Pole (TP) basins show large discrepancies in precipitation magnitudes and spatiotemporal patterns, which poses a great challenge to hydrological simulations in the TP basins. In this study, a gridded (10 km x 10 km) daily precipitation dataset is constructed through a random-forest-based machine learning algorithm (RF algorithm) correction of the ERA5 precipitation estimates based on 940 gauges in 11 upper basins of TP for 1951-2020. The dataset is evaluated by gauge observations at point scale and is inversely evaluated by the Variable Infiltration Capacity (VIC) hydrological model linked with a glacier melt algorithm (VIC-Glacier). The corrected ERA5 (ERA5_cor) agrees well with gauge observations after eliminating the severe overestimation in the original ERA5 precipitation. The corrections greatly reduce the original ERA5 precipitation estimates by 10%-50% in 11 basins of the TP and present more details on precipitation spatial variability. The inverse hydrological model evaluation demonstrates the accuracy and rationality, and we provide an updated estimate of runoff components contribution to total runoff in seven upper basins in the TP based on the VIC-Glacier model simulations with the ERA5_cor precipitation. This study provides good precipitation estimates with high spatiotemporal resolution for 11 upper basins in the TP, which are expected to facilitate the hydrological modeling and prediction studies in this high mountainous region. Significance StatementThe Third Pole (TP) is the source of water to the people living in the areas downstream. Precipitation is the key driver of the terrestrial hydrological cycle and the most important atmospheric input to land surface hydrological models. However, none of the current precipitation data are equally good for all the TP basins because of high variabilities in their magnitudes and spatiotemporal patterns, posing a great challenge to the hydrological simulation. Therefore, in this study, a gridded daily precipitation dataset (10 km x 10 km) is reconstructed through a random-forest-based machine learning algorithm correction of ERA5 precipitation estimates based on 940 gauges in 11 TP basins for 1951-2020. The data eliminate the severe overestimation of original ERA5 precipitation estimates and present more reasonable spatial variability, and also exhibit a high potential for hydrological application in the TP basins. This study provides long-term precipitation data for climate and hydrological studies and a reference for deriving precipitation in high mountainous regions with complex terrain and limited observations.
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