Projecting Future Droughts Across China Based On The SPI/SPEI Index And RRV Framework

Climate warming affects the hydrological cycle and thereby exacerbates drought.China is one of the countries most affected by drought in East Asia.In recent years,droughts have occurred frequently throughout China,which has seriously affected social stability and economic development.The increasingly severe drought under climate warming is putting severe tests on the development and utilization of water resources in China.In order to fully understand and manage drought and reduce its impact on water resources,it is necessary to assess the drought situation and simulate future drought conditions over China.This paper takes the main river basins of China as a study area,assesses its future climate change,analyzes the future trends and causes of potential evapotranspiration,and reveals the impact of climate warming on future drought.The main work and conclusions are as follows:(1)We detect the spatiotemporal trends of climate variables in China.The variations in climate variables for the future projected period of 2021-2050 compared with the baseline period of 1976-2005 show that the precipitation and mean,maximum and minimum temperatures is projected to increase from the southeastern coast to the northwestern inland areas of China.The solar radiation is projected to increase in most areas of China,except the northern part of the Yangtze River basin.The relative changes in relative humidity,wind speed,and atmospheric pressure are projected to be small.Under the RCP8.5 scenario,the increase rate is projected to be generally higher than RCP4.5.The trend test results of potential evapotranspiration-related climate variables during 2021-2050 show that the maximum and minimum temperatures are projected to have a significant increase in most areas of China.Wind speed is projected to decrease significantly in the upper Yangtze River basin and the junctions of the Northwest River basins and Southwest River basins.Relative humidity is projected to decrease significantly in the Huaihe River basin,Northwest River basins and parts of the Yangtze River basin.Solar radiation is projected to increase significantly in most areas of China.Atmospheric pressure is projected to increase significantly in parts of the Songhuajiang River basin,but decrease significantly in the upper Yangtze River basin and the southwest of the Northwest River basins.Under both the RCP8.5 and RCP4.5 scenarios,the minimum and maximum temperatures and solar radiation spatial change trends are projected to be generally the same,but regional differences can be found in wind speed,relative humidity and atmospheric pressure.(2)We evaluate the spatiotemporal dynamics of potential evapotranspiration and discuss the causes of potential evapotranspiration changes in China during 2021-2050.The variations in potential evapotranspiration for the future projected period of 2021-2050 compared with the baseline period of 1976-2005 show that potential evapotranspiration is projected to increase across China and increase significantly in the southernern Tibetan Plateau and the northeastern and eastern China.The spatial changes unerd the RCP8.5 scenario are similar to those under RCP4.5,but the increases are greater than RCP4.5.The trend test results during 2021-2050 show that the potential evapotranspiration under both the RCP4.5 and RCP8.5 scenarios are projected to have a significant increase tendency,while the Sonhuajiang River basin is projected to have a decrease trend in winter.The sensitivity analysis results show that most areas of China are most sensitive to the highest temperature under RCP4.5,while in parts of the Southwestern River basins,Yangtze River basin,Zhujiang River basin,Southeast River basins and some Songhuajiang River basin the most sensitive climate variable is solar radiation.Under the RCP8.5 scenario,the most sensitive climate variable in most areas of China is solar radiation.The increase in potential evapotranspiration during the future period is due to the maximum temperature in the northern river basins and the significant increase of solar radiation in the southern river basins.The significant upward trend of potential evapotranspiration is attributed to the three major influencing factors of maximum temperature,solar radiation and minimum temperature.(3)We analyzes the spatiotemporal changes of drought in China and the impact of climate warming on droughts.The SPEI results during 2021-2050 show that future dryness conditions are projected to be intensify in most areas of China,and the increases from the southeastern coast to the northwest inland areas of China are projected to increase gradually,with a relatively serious dryness condition in the Northwest River basins and Yellow River basin.The trend test results show that most areas of China are projected to have a significant dryness trend under climate warming in the future,and the tendency is projected to shift from the southwestern to northeastern China to the northwestern and southeastern China.The results of the drought characteristics during 2021-2050 show that the drought duration,frequency and severity are projected to increase gradually from the southeastern and northeastern China to the northwestern China(especially in the Northwest River basins and Southwest River basins).Simultaneously,extreme drought events are more likely to occur in regions with greater temperature increases(the Northwest River basins).The SOM-Kmeans clustering results show that the regional zoning map of future drought conditions is bounded by the 400-mm precipitation line of China.The drought conditions of the region northwest of the line are the most complex and severe.The drought conditions under the RCP8.5 scenario are more severe than that under RCP4.5.(4)We discuss the spatial distribution and changes of the river basin health status based on the basin's responses to dryness conditions in China under different thresholds of dryness conditions,and analyzes the impact of climate warming on the river basin health status.The results of precipitation and its difference from the potential evapotranspiration show that precipitation is projected to increase from the northwestern inland to the southeastern coast areas of China and the increase tendency is projected to be significant in parts of western and northern China.water deficits are projected to occur in most areas of China and will significantly increase in the next 30 years due to global warming effects.The spatial pattern and change trend of drought-based RRV in various river basins in China during 2021-2050 show that the health conditions of the northern river bains are projected to be unhealthy and deteriorate significantly,while southern river basins is projected to be generally healthy.The health conditions in the Northwest River basins and Yellow River basin are projected to be unhealthy and deteriorate significantly under global warming in the future,and the southern river basins are projected to have healthy conditions.The health status is worse under the RCP8.5 scenario than that under RCP4.5.The results comparison for the three thresholds shows that normal dryness is applicable to most areas of northeastern,northern and southern China,while abnormal dryness is applicable to the other areas.