| 191. |
- Hu, Zengyun, et al.
(författare)
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DISO: A rethink of Taylor diagram
- 2019
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 39:5, s. 2825-2832
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Tidskriftsartikel (refereegranskat)abstract
- Climate models use quantitative methods to simulate the interactions of the important drivers of climate system, to reveal the corresponding physical mechanisms, and to project the future climate dynamics among atmosphere, oceans, land surface and ice, such as regional climate models and global climate models. A comprehensive assessment of these climate models is important to identify their different overall performances, such as the accuracy of the simulated temperature and precipitation against the observed field. However, until now, the comprehensive performances of these models have not been quantified by a comprehensive index except the existed single statistical index, such as correlation coefficient (r), absolute error (AE), and the root‐mean‐square error (RMSE). To address this issue, therefore, in this study, a new comprehensive index Distance between Indices of Simulation and Observation (DISO) is developed to describe the overall performances of different models against the observed field quantitatively. This new index DISO is a merge of different statistical metrics including r, AE, and RMSE according to the distance between the simulated model and observed field in a three‐dimension space coordinate system. From the relationship between AE, RMSE, and RMS difference (RMSD) (i.e., standard deviation [SD] of bias time series), the new index also has the information of RMSD which is the statistical index in Taylor diagram. An example is applied objectively to display the applications of DISO and Taylor diagram in identifying the overall performances of different simulated models. Overall, with the strong physical characteristic of the distance in three dimensional space and the strict mathematical proof, the new comprehensive index DISO can convey the performances among different models. It can be applied in the comparison between different model data and in tracking changes in their performances.
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| 192. |
- Hu, Zengyun, et al.
(författare)
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“Dry gets drier, wet gets wetter”: A case study over the arid regions of central Asia
- 2019
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 39:2, s. 1072-1091
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 Royal Meteorological Society The “dry gets drier, wet gets wetter” (DGDWGW) paradigm well describes the pattern of precipitation changes over the oceans. However, it has also been usually considered as a simplified pattern of regional changes in wet/dry under global warming, although GCMs mostly do not agree this pattern over land. To examine the validity of this paradigm over land and evaluate how usage of drought indices estimated from different hydrological variables affects detection of regional wet/dry trends, we take the arid regions of central Asia as a case study area and estimate the drying and wetting trends during the period of 1950–2015 based on multiple drought indices. These indices include the standardized precipitation index (SPI), the standardized precipitation evapotranspiration index (SPEI), the Palmer drought severity index (PDSI) and self-calibrating PDSI (sc_PDSI) with both the Thornthwaite (th) and Penman–Monteith (pm) equations in PDSI calculation (namely, PDSI_th, PDSI_pm, sc_PDSI_th and sc_PDSI_pm). The results show that there is an overall agreement among the indices in terms of inter-annual variation, especially for the PDSIs. All drought indices except SPI show a drying trend over the five states of central Asia (CAS5: including Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan). The four PDSIs and SPEI reveal a wetting tendency over the northwestern China (NW; including Xinjiang Uygur Autonomous Region and Hexi Corridor). The contrasting trends between CAS5 and NW can also be revealed in soil moisture (SM) variations. The nonlinear wet and dry variations are dominated by the 3–7 years oscillations for the indices. Relationships between the six indices and climate variables show the major drought drivers have regional features: with mean temperature (TMP), precipitation total (PRE) and potential evapotranspiration (PET) for CAS5, and PRE and PET for NW. Finally, our analyses indicate that the dry and wet variations are strongly correlated with the El Niño/Southern Oscillation (ENSO).
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| 193. |
- Hu, Z. Y., et al.
(författare)
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Evaluation of three global gridded precipitation data sets in central Asia based on rain gauge observations
- 2018
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38:9, s. 3475-3493
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Tidskriftsartikel (refereegranskat)abstract
- The accuracies of gridded precipitation data sets are important for regional climate studies and hydrological models. In this study, the performances of Global Precipitation Climatology Centre (GPCC) V7, Climatic Research Unit (CRU) TS 3.22 and Willmott and Matsuura (WM) precipitation data sets were examined over central Asia by comparing them against observed precipitation records (OBS) from 586 meteorological stations during 1901-2010. The results show that all the three gridded data sets underestimated the observed precipitation at annual and monthly scales, especially in mountainous areas. Both GPCC and WM underestimated seasonal precipitation, especially for spring precipitation. Among the three gridded data sets, GPCC had the highest correlation and lowest bias compared with CRU and WM when against the OBS. WM had a higher correlation than that of CRU, and its bias was larger than that of CRU. In terms of the drought and heavy rainfall events, CRU had the best performance in capturing drought events, and GPCC was best at representing heavy rainfall events. These differences in the performances between the three gridded data sets were primarily induced by their different interpolation methods and the numbers of available meteorological stations used in the interpolations of the three gridded data sets. Therefore, compared to the other two data sets, GPCC is more suitable for studies of long-term precipitation variations over central Asia.
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| 194. |
- Hu, Z. Y., et al.
(författare)
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Groundwater Depletion Estimated from GRACE: A Challenge of Sustainable Development in an Arid Region of Central Asia
- 2019
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 11:16
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Tidskriftsartikel (refereegranskat)abstract
- Under climate change and increasing water demands, groundwater depletion has become regional and global threats for water security, which is an indispensable target to achieving sustainable developments of human society and ecosystems, especially in arid and semiarid regions where groundwater is a major water source. In this study, groundwater depletion of 2003-2016 over Xinjiang in China, a typical arid region of Central Asia, is assessed using the gravity recovery and climate experiment (GRACE) satellite and the global land data assimilation system (GLDAS) datasets. In the transition of a warm-dry to a warm-wet climate in Xinjiang, increases in precipitation, soil moisture and snow water equivalent are detected, while GRACE-based groundwater storage anomalies (GWSA) exhibit significant decreasing trends with rates between-3.61 +/- 0.85 mm/a of CSR-GWSA and -3.10 +/- 0.91 mm/a of JPL-GWSA. Groundwater depletion is more severe in autumn and winter. The decreases in GRACE-based GWSA are in a good agreement with the groundwater statistics collected from local authorities. However, at the same time, groundwater abstraction in Xinjiang doubled, and the water supplies get more dependent on groundwater. The magnitude of groundwater depletion is about that of annual groundwater abstraction, suggesting that scientific exploitation of groundwater is the key to ensure the sustainability of freshwater withdrawals and supplies. Furthermore, GWSA changes can be well estimated by the partial least square regression (PLSR) method based on inputs of climate data. Therefore, GRACE observations provide a feasible approach for local policy makers to monitor and forecast groundwater changes to control groundwater depletion.
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| 195. |
- 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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| 196. |
- Huang, Z., et al.
(författare)
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Clarification of dominating drivers for streamflow changes in the upper reach of Mekong River Basin
- 2023
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Ingår i: Journal of Hydrology-Regional Studies. ; 48
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Tidskriftsartikel (refereegranskat)abstract
- Study region: Lancang River Basin (LRB)Study focus: Previous studies provided different results in terms of the roles played by climate change and human activities, leaving a knowledge gap in the complex streamflow variability and its physical causes in LRB. In the study, a Budyko framework-aided analytical approach was applied to explore the streamflow decrease in LRB and its physical causes, by especially clarifying the different performances of eight Budyko equations and the influences of diverse baseline periods.New hydrological insights for the region: Results revealed that the four parametric Budyko equations can provide proper parameters to reflect changes in catchment characteristics (including human activities) and their influences, and thus, they performed better than the four non-parametric Budyko equations. It was further found that more reasonable attribution results of streamflow change were obtained when a longer baseline period (at least 20 years) was used. Results also indicated that human activities (accounting for-158.9%) dominated the streamflow decrease during the transition period (1986-2004), by offsetting the positive effects of climate change (accounting for 58.9%). During the impact period (2005-2015), human activities (accounting for-65.6%) still dominated the streamflow decrease, and climate change (accounting for-34.4%) further aggravated the streamflow decrease in LRB.
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| 197. |
- Ikram, F., et al.
(författare)
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Evaluation of Three Genesis Potential Indices for Tropical Cyclogenesis in the Arabian Sea: Two Case Studies Using WRF and ERA5
- 2022
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Ingår i: Monthly Weather Review. - 0027-0644. ; 150:12
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Tidskriftsartikel (refereegranskat)abstract
- Tropical cyclones (TCs) generated over the Arabian Sea can cause significant damage to infrastructure, human lives, landfall, and property near inshore and maritime trade route areas. A key to successful prediction of TCs is a skillful prediction of potential cyclogenesis locations. This study focuses on evaluating three genesis potential indices (GPIs) derived from a global reanalysis (ERA5) and dynamically downscaling using a regional model (WRF) for two TC cases: Gonu in 2007 and Kyarr in 2019, selected by analyzing the accumulated cyclone energy trend from the International Best Track Archive for Climate Stewardship (IBTrACS) dataset over the period of 1981–2019. The two TCs belong to category 4 and above on the Saffir–Simpson scale. To test the sensitivity of downscaling to cumulus parameterizations, two WRF experiments were conducted using the Kain–Fritsch and New Tiedke cumulus schemes, respectively. The calculated genesis locations with help of the three GPIs were compared with IBTrACS. The results show that 1) all indices have reasonable skills in reproducing genesis locations, although their performances differ somewhat; 2) the dynamic downscaling with two WRF experiments added value to the study by comparing two numerical schemes for estimating genesis locations; and 3) WRF with the New Tiedke and Kain–Fritsch schemes showed good skill in reproducing the spatial distribution of the most relevant dynamical parameters. The pattern correlations are well correlated with environmental parameters of untransformed GPI and higher correlations with binary logarithmic transformed GPI. The applicability to other cyclones is also tested (e.g., TC Nilofar in 2014) with encouraging results. This study demonstrates the usefulness of GPIs for forecasting TC genesis in the region.
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| 198. |
- Irannezhad, Masoud, 1983, et al.
(författare)
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Analysing the variability and trends of precipitation extremes in Finland and their connection to atmospheric circulation patterns
- 2017
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 37, s. 1053-1066
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 Royal Meteorological Society Ten precipitation indices recommended by the Expert Team on Climate Change Detection and Indices were used to analyse spatial distribution and temporal changes in annual amount, intensity, frequency and duration of precipitation statistics based on daily data with a focus on extremes in Finland during 1 961–2011. Also, the connections between these high resolution (10 km) precipitation indices and six influential atmospheric circulation patterns (ACPs) for climate variability in Finland were studied. On the country scale, the results suggest significant increases in the amount and intensity of precipitation extremes, more precipitation days, and no clear changes in wet and dry spells. Both intensity and frequency of precipitation extremes over Finland decrease from south and southwest to north. The only exception is the distribution of precipitations days which is generally more frequent over eastern and upper areas of northern Finland. Wet (dry) spells were typically longer in the western (eastern) part of Finland. Significant increases in annual total wet-day precipitation, very wet days precipitation and simple daily intensity index were found over most parts of Finland during 1961–2011. Increasing trends in both extremely wet days and maximum 1-day precipitation were mostly observed in western, eastern, central and northern Finland. Such spatial pattern was also identified for significant increases in the frequency of heavy and very heavy precipitation days. The precipitation days increased over small parts of western, eastern and northern Finland. Wet spells showed lengthening trends in several grids over southwestern Finland, while dry spells lengthened in some areas over the entire country except southern parts. These variations in precipitation statistics were found to be significantly correlated with the East Atlantic/West Russia, East Atlantic, Scandinavia and Polar patterns.
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| 199. |
- Irannezhad, Masoud, et al.
(författare)
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Century-long variability and trends in daily precipitation characteristics at three Finnish stations
- 2016
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Ingår i: Advances in Climate Change Research. - : Elsevier BV. - 1674-9278. ; 7, s. 54-69
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 National Climate Center (China Meteorological Administration) Long-term variations and trends in a wide range of statistics for daily precipitation characteristics in terms of intensity, frequency and duration in Finland were analysed using precipitation records during 1908–2008 from 3 meteorological stations in the south (Kaisaniemi), centre (Kajaani) and north (Sodankylä). Although precipitation days in northern part were more frequent than in central and southern parts, daily precipitation intensity in the south was generally higher than those in the centre and north of the country. Annual sum of very light precipitation (0 mm < daily precipitation ≤ long-term 50th percentile of daily precipitation more than 0 mm) significantly (p < 0.05) decreased over time, with the highest rate in northern Finland. These decreasing trends might be the result of significant increases in frequency of days with very light precipitation at all the stations, with the highest and lowest rates in northern and southern Finland, respectively. Ratio of annual total precipitation to number of precipitation days also declined in Finland over 1908–2008, with a decreasing north to south gradient. However, annual duration indices of daily precipitation revealed no statistically significant trends at any station. Daily precipitation characteristics showed significant relationships with various well-known atmospheric circulation patterns (ACPs). In particular, the East Atlantic/West Russia (EA/WR) pattern in summer was the most influential ACP negatively associated with different daily precipitation intensity, frequency and duration indices at all three stations studied.
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| 200. |
- Irannezhad, M., et al.
(författare)
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Compound climate extreme events threaten migratory birds’ conservation in western U.S
- 2022
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Ingår i: Sustainable Horizons. - : Elsevier BV. - 2772-7378. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- In a warming world, more intense and frequent compound climate extreme events pose serious challenges to biodiversity and conservation on Earth as one of the 2030 United Nations’ sustainable development goals (SDGs): “Life On Land” (SDG 15). In summer 2020, concurrent swelling wildfires and a sudden cold snap in the western U.S. killed a massive number of migratory birds. In August 2020, the hot and humid weather in response to the wildfire radiation and the oceanic evaporation could result in killing heat stress for migratory birds along the coastal shoreline, particularly in California. The heat and smoke of wildfires forced the migratory birds to abandon such feeding grounds towards inland regions, where water and food are naturally scarce, before being physiologically ready for their long-distance flyways. Then, a cold snap during 8–11 September in the Rocky Mountain states in the western U.S. urged those already weak migratory birds to fly southward before effectively recovering their physical and mental capabilities. This durable extreme starvation finally brought the skinny migrants low in the southwestern U.S. However, such ecological cascade effects of compound climate risks have rarely been acknowledged as a serious threat to migratory birds’ conservation in both scientific literature and ecosystems’ management practice. To improve our chances of saving birds’ biodiversity on Earth, hence, conscious policies and sustained efforts must immediately be arranged through SDG 13 (“Climate Actions”) based on scientific evidence and knowledge.
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