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Sökning: LAR1:gu > Chen Deliang 1961

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41.
  • Cai, Ziyi, et al. (författare)
  • Assessing Arctic wetting: Performances of CMIP6 models and projections of precipitation changes
  • 2024
  • Ingår i: Atmospheric Research. - 0169-8095. ; 297
  • Tidskriftsartikel (refereegranskat)abstract
    • The Arctic region is experiencing a notable increase in precipitation, known as Arctic wetting, amidst the backdrop of Arctic warming. This phenomenon has implications for the Arctic hydrological cycle and numerous socio-ecological systems. However, the ability of climate models to accurately simulate changes in Arctic wetting has not been thoroughly assessed. In this study, we analyze total precipitation in the Arctic using station data, multiple reanalyses, and 35 models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6). By employing the moisture budget equation and an evaluation method for model performance with ERA5 reanalysis as a reference, we evaluated the models' capability to reproduce past Arctic wetting patterns. Our findings indicate that most reanalyses and models are able to replicate Arctic wetting. However, the CMIP6 models generally exhibit an overestimation of Arctic wetting during the warm season and an underestimation during the cold season from 1979 to 2014 when compared to the ERA5 reanalysis. Further investigation reveals that the overestimation of wetting during the warm season is largest over the Arctic Ocean's northern part, specifically the Canadian Arctic Archipelago, and is associated with an overestimation of atmospheric moisture transport. Conversely, the models significantly underestimate wetting over the Barents-Kara Sea during the cold season, which can be attributed to an underestimation of evaporation resulting from the models' inadequate representation of sea ice reduction in that region. The models with the best performance in simulating historical Arctic wetting indicate a projected intensification of Arctic wetting, and optimal models significantly reduce uncertainties in future projections compared to the original models, particularly in the cold season and oceanic regions. Our study highlights significant biases in the CMIP6 models' simulation of Arctic precipitation, and improving the model's ability to simulate historical Arctic precipitation could reduce uncertainties in future projections.
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42.
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43.
  • Cai, Z. Y., et al. (författare)
  • Arctic Warming Revealed by Multiple CMIP6 Models: Evaluation of Historical Simulations and Quantification of Future Projection Uncertainties
  • 2021
  • Ingår i: Journal of Climate. - : American Meteorological Society. - 0894-8755 .- 1520-0442. ; 34:12, s. 4871-4892
  • Tidskriftsartikel (refereegranskat)abstract
    • The Arctic has experienced a warming rate higher than the global mean in the past decades, but previous studies show that there are large uncertainties associated with future Arctic temperature projections. In this study, near-surface mean temperatures in the Arctic are analyzed from 22 models participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6). Compared with the ERA5 reanalysis, most CMIP6 models underestimate the observed mean temperature in the Arctic during 1979-2014. The largest cold biases are found over the Greenland Sea the Barents Sea, and the Kara Sea. Under the SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios, the multimodel ensemble mean of 22 CMIP6 models exhibits significant Arctic warming in the future and the warming rate is more than twice that of the global/Northern Hemisphere mean. Model spread is the largest contributor to the overall uncertainty in projections, which accounts for 55.4% of the total uncertainty at the start of projections in 2015 and remains at 32.9% at the end of projections in 2095. Internal variability uncertainty accounts for 39.3% of the total uncertainty at the start of projections but decreases to 6.5% at the end of the twenty-first century, while scenario uncertainty rapidly increases from 5.3% to 60.7% over the period from 2015 to 2095. It is found that the largest model uncertainties are consistent cold bias in the oceanic regions in the models, which is connected with excessive sea ice area caused by the weak Atlantic poleward heat transport. These results suggest that large intermodel spread and uncertainties exist in the CMIP6 models' simulation and projection of the Arctic near-surface temperature and that there are different responses over the ocean and land in the Arctic to greenhouse gas forcing. Future research needs to pay more attention to the different characteristics and mechanisms of Arctic Ocean and land warming to reduce the spread.
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44.
  • Cai, Z. Y., et al. (författare)
  • Interdecadal variability of the warm Arctic-cold Eurasia pattern linked to the Barents oscillation
  • 2023
  • Ingår i: Atmospheric Research. - : Elsevier BV. - 0169-8095. ; 287
  • Tidskriftsartikel (refereegranskat)abstract
    • Observed winter near-surface air temperature anomalies in the Northern Hemisphere have exhibited a warm Arctic-cold Eurasia (WACE) pattern with interdecadal variation in recent decades, but the exact mechanism behind WACE is still under debate. This study used reanalysis data and climate model simulations to investigate the interdecadal variability of the WACE pattern on a centennial scale, as well as the role of atmospheric circulations. It is found that the second mode of atmospheric variability over the North Atlantic-Arctic region, known as the Barents oscillation (BO), played a dominant role in regulating the interdecadal variability of WACE. The atmospheric circulation associated with the positive phase of the BO corresponds to an anomalous enhancement of the quasi-barotropic anticyclone near the southern Barents-Kara Seas (BKS) and the North Atlantic, as well as a weakening of the mid-latitude westerly jet. This atmospheric circulation anomaly favors the northward transport of atmospheric heat and moisture to the BKS from the mid-latitudes, resulting in an increased air temperature through downward longwave radiation. Concurrently cold air is transported from the polar region to Central Eurasia (CE), decreasing air temperature over CE. The amplified temperature anomaly dipole results in the decadal enhancement of the WACE pattern. The atmospheric circulation anomalies related to the negative phase of the BO are the opposite, which in turn leads to the decadal weakening of the WACE pattern. Our results further support the important role of internal atmospheric variability in the formation of WACE and emphasize that the atmospheric circulation associated with the BO is the main driver of WACE decadal variability over the past century.
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45.
  • Chai, C. H., et al. (författare)
  • Future snow changes and their impact on the upstream runoff in Salween
  • 2022
  • Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 26:18, s. 4657-4683
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding the hydrological processes related to snow in global mountainous regions under climate change is necessary for achieving regional water and food security (e.g., the United Nation's Sustainable Development Goals 2 and 6). However, the impacts of future snow changes on the hydrological processes in the high mountains of the "Third Pole" are still largely unclear. In this study, we aimed to project future snow changes and their impacts on hydrology in the upstream region of the Salween River (USR) under two shared socioeconomic pathway (SSP) scenarios (SSP126 and SSP585) using a physically based cryosphere-hydrology model. We found that the climate would become warmer (0.2 degrees C per decade under SSP126 and 0.7 degrees C per decade under SSP585) and wetter (5mm per decade under SPP126 and 27.8mm per decade under SSP585) in the USR in the future under these two SSPs. In this context, the snowfall, snow cover, snow water equivalent, and snowmelt runoff are projected to exhibit significant decreasing trends during 1995-2100, and the decreases are projected to be most prominent in summer and autumn. The future (2021-2100) snowmelt runoff is projected to significantly increase in spring compared with the reference period (1995-2014), which would benefit the availability of water resources in the growing season. The annual total runoff would significantly increase in all of the future periods due to increased rainfall, which would increase the availability of water resources within the basin, but the high peak flow that occurs in summer may cause rain flooding with short duration and high intensity. Compared with the reference period (the contribution of snowmelt runoff to the total runoff was determined to be 17.5 %), the rain- and snow-dominated pattern of runoff would shift to a rain-dominated pattern after the near term (2021-2040) under SSP585, whereas it would remain largely unchanged under SSP126. Climate change would mainly change the pattern of the snowmelt runoff, but it would not change the annual hydrograph pattern (dominated by increased rainfall). These findings improve our understanding of the responses of cryosphere-hydrological processes under climate change, providing valuable information for integrated water resource management, natural disaster prevention, and ecological environmental protection at the Third Pole.
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46.
  • Chai, J., et al. (författare)
  • A robust equatorial Pacific westerly response to tropical volcanism in multiple models
  • 2020
  • Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 55
  • Tidskriftsartikel (refereegranskat)abstract
    • After each of the 1963 Agung, 1982 El Chichon, and 1991 Pinatubo eruptions, an El Nino was observed. The increased likelihood of an El Nino after a tropical eruption has also been found in long-term reconstructed proxy data. Through examining simulations over the last millennium by 11 different models, we show that a tropical volcano eruption can robustly excite a western-to-central equatorial Pacific (WCEP) westerly anomaly at 850 hPa in eight out of the 11 models; such a westerly anomaly is favorable for El Nino development. Under the volcanic forcing, there are significant extratropical continent surface cooling and tropical drying with negative precipitation anomalies over the South-South East Asia (SSEA), West African monsoon, and Intertropical Convergence Zone (ITCZ) regions. This common precipitation suppression response occurs in most of the models. Sensitivity experiments show that a WCEP westerly anomaly can be excited by the tropical land cooling, especially the SSEA cooling induced precipitation suppression rather than by the extratropical land surface cooling. Theoretical results show that a WCEP westerly anomaly is excited due to a Gill response to reduced precipitation over the SSEA and West African monsoon regions; and the SSEA contributes more than the West African monsoon does. The ITCZ weakening, however, excites an easterly wind anomaly. The models with more sensitive convective feedback tend to simulate an El Nino more easily, while a failed simulation of an El Nino after a robust westerly anomaly in some models calls for further studies on these models' delayed responses to radiative forcing induced by volcano eruptions.
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47.
  • Chen, Aifang, 1990, et al. (författare)
  • Assessing reliability of precipitation data over the Mekong River Basin: A comparison of ground-based, satellite, and reanalysis datasets
  • 2018
  • Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38:11, s. 4314-4334
  • Tidskriftsartikel (refereegranskat)abstract
    • Accurate precipitation data are the basis for hydro-climatological studies. As a highly populated river basin, with the biggest inland fishery in Southeast Asia, freshwater dynamics is extremely important for the Mekong River Basin (MB). This study focuses on evaluating the reliability of existing gridded precipitation datasets both from satellite and reanalysis, with a ground observations-based gridded precipitation dataset as the reference. Two satellite products (Tropical Rainfall Measuring Mission [TRMM] and the Precipitation Estimation from Remote Sensing Information using an Artificial Neural NetworkClimate Data Record [PERSIANN-CDR]), as well as three reanalysis products (Modern-Era Retrospective analysis for Research and Applications [MERRA2], the European Centre for Medium-Range Weather Forecasts interim reanalysis [ERA-Interim], and the Climate Forecast System Reanalysis [CFSR]) were compared with the Asian PrecipitationHighly Resolved Observational Data Integration Towards Evaluation of Water Resources (APHRODITE) over the MB. The APHRODITE was chosen as the reference for the comparison because it was developed based on ground observations and has also been selected as reference data in previous studies. Results show that most of the assessed datasets are able to capture the major climatological characteristics of precipitation in the MB for the 10-year study period (1998-2007). Generally, both satellite data (TRMM and PERSIANN-CDR) show higher reliability than reanalysis products at both spatial and temporal scales across the MB, with the TRMM outperforming when compared to the PERSIANN-CDR. For the reanalysis products, MERRA2 is more reliable in terms of temporal variability, but with some underestimation of precipitation. The other two reanalysis products CFSR and ERA-Interim are relatively unreliable due to large overestimations. CFSR is better positioned to capture the spatial variability of precipitation, while ERA-Interim shows inconsistent spatial patterns but more realistically resembles the daily precipitation probability. These findings have practical implications for future hydro-climatological studies.
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48.
  • Chen, A. F., et al. (författare)
  • An analysis of the spatial variation of tropical cyclone rainfall trends in Mainland Southeast Asia
  • 2023
  • Ingår i: International Journal of Climatology. - 0899-8418. ; 43:13, s. 5912-26
  • Tidskriftsartikel (refereegranskat)abstract
    • Tropical cyclones (TCs) and the associated rainfall (TCR) have received increasing attention because of their catastrophic damages. Due to the differences in TC characteristics and TCR in different ocean basins, the changes in TCR would be complicated for areas receiving TC landfalling from multi-basins. Therefore, separating TCR and TC characteristics from the formation basins can offer more insights for accurately evaluating TCR in the landfalling areas. Here we selected the TC-prone Mainland Southeast Asia (MSEA) to investigate changes in TCR regarding TC characteristics from the surrounding formation basins from 1983 to 2020. Results show that the interannual variability of the total TCs influencing MSEA (MSEA-ALL-TC) characteristics, including number, total duration, maximum intensity and accumulated cyclone energy, was dominated by the TCs originating from the Western North Pacific (WNP-TC). However, the total TCR was controlled by the TCs originating from the WNP and the South China Sea (SCS-TC), whose influence on TCR was concentrated in the eastern MSEA. TCR associated with TCs originating from the Bay of Bengal was relatively small and concentrated in the western MSEA. For the whole MSEA, the total TCR contributed up to 47% of the annual extreme rainfall amount. Annual TCR presented significant decreasing trends in the southeast MSEA, while increasing trends exist in the northeast. These contrasting trends are attributed to the reduced tendency of WNP-TC track density and the increased SCS-TC rainfall rate. We also found that the SCS-TC induced a higher rainfall rate than the other two basins. The TC characteristics of number, total duration, maximum intensity and accumulated cyclone energy were significantly correlated with TCR in each formation basin, with the highest correlation of the total duration. This study improves our understanding of the influence of changes in TC characteristics on TCR in the TC multi-source region.
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49.
  • Chen, Aifang, 1990, et al. (författare)
  • Flood impact on Mainland Southeast Asia between 1985 and 2018 — The role of tropical cyclones
  • 2020
  • Ingår i: Journal of Flood Risk Management. - : Wiley. - 1753-318X. ; 13:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Floods are disastrous natural hazards accused of human live losses. As a flood‐prone area, Mainland Southeast Asia (MSEA) has often been hit by floods, resulting in the highest fatality in the world. Despite the destructive flood impacts, how has flood occurrence changed over the past decades, and to what extent did floods affect the MSEA are not yet clear. Using the Dartmouth Flood Observatory large flood data archive, we aim to assess the trend of flood occurrence in the MSEA in 1985–2018, and quantify the associated impacts on humans. Particularly, the contribution of tropical cyclone (TC) landfall induced floods (TCFloods) is quantified, because of the frequent TC landfalls. Results show that (a) occurrence and maximum magnitude of floods by all causes (ALLFloods) significantly increased (p < .01), but not for TCFloods; (b) On average, TCFloods accounted for 24.6% occurrence of ALLFloods; (c) TCFloods caused higher mortality and displacement rate than ALLFloods did. As low flood protection standards in Cambodia and Myanmar is considered a reason for high flood‐induced mortalities, building higher flood protection standards should be taken as a priority for mitigating potential flood impacts. With quantifying flood occurrence and impacts, this study offers scientific understandings for better flood risk management.
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50.
  • Chen, Aifang, 1990, et al. (författare)
  • Large net forest loss in Cambodia's Tonle Sap Lake protected areas during 1992-2019
  • 2022
  • Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 51
  • Tidskriftsartikel (refereegranskat)abstract
    • Historical land-use practices have caused forest loss in Cambodia's Tonle Sap Lake area (TSLA), the largest freshwater lake in Southeast Asia. However, it remains unclear if this deforestation trend had continued since 2001 when the land was designated as protected areas. Using satellite imagery, we investigated forest conversion flows and fragmentation patterns in the TSLA for 1992-2001, 2001-2010, and 2010-2019, respectively. Results show substantial forest losses and fragmentations occurring at the lower floodplain where the protected areas are located until 2010, with some forest regain during 2010-2019. The land conversions indicated that forest clearing and agricultural farming were the primary causes for observed extensive forest loss during 1992-2010. Hence, despite the creating of protected areas in 2001, our findings reveal the persistence of alarming forest loss in the TSLA until 2010. On the other hand, while net forest loss has stopped after 2010, forest regain during 2010-2019 is way too small to restore the region's total forest area to even the level when the protected areas were established. Thus, more effective planning and implementations of forest management and restoration policies are needed for the TSLA.
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