Assessment On Water Supply Security In China Under Climate Change

Global climate change significantly affects natural environment,agriculture,water resources and other systems.Assessing the challenges to geographical environment and water resources supply are of great significance to cope with climate change,environmental protection,water resource allocation,and flood control and drought prevention.In this paper,an index system is constructed to evaluate the vulnerability of the geographical environment so as to clarify the challenges to geographical environment in China,and then the supply of water resources is evaluated by estimating the amount of water resources in the future under climate change.Specifically,the index system is constructed firstly from four aspects: topography,climatic factors,vegetation cover and irrigation conditions,which is used to evaluate the spatial distribution characteristics and temporal trends of environment vulnerability in China.Then,the output data from CMIP5,including temperature,precipitation,relative humidity,wind speed and leaf area index,are used to calculate the reference evapotranspiration under four climate change scenarios based on the Penman-Monteith formula.And then the temporal and spatial variation characteristics of environmental vulnerability and water resources(including evapotranspiration,drought index and runoff)in the future period are predicted.It will provide decision support for future water resources protection and deployment,regional environmental protection and sustainable development.The main conclusions of this paper are as follows:(1)China is becoming more vulnerable since 2000.The western region has the highest environmental vulnerability,both in the past and in the future.The dynamic trend in the past shows that the level of environmental vulnerability has increased significantly since 2000,and the ecological environment has become more vulnerable.The environmental vulnerability assessment in the future shows that the spatial distribution of environmental vulnerability under the four RCP scenarios is not very different,and the environmental vulnerability is highest under RCP 8.5,obviously identified in the northwest and southeast regions.The temporal variation characteristics of environmental vulnerability under all scenarios show an increasing trend.Especially in the RCP 8.5 scenario,the environmental vulnerability has the fastest growth rate.(2)The evapotranspiration in the future period shows an increasing trend,and the aridification is obvious.The reference evapotranspiration shows an upward trend in all agricultural regions,but the growth rate was different.On the whole,the fastest growth rate are located in the Huang-Huai-Hai Region,the middle and lower regions of the Yangtze River and the South China Region,while the growth rate of the Qinghai-Tibet Plateau Region is slowest.The seasonal reference evapotranspiration values all show upward trends during 2020-2099,with the fastest growth rate in summer and slowest growth in winter.The analysis of contribution rate of climatic factors shows that temperature is always the main contributor to the change in reference evapotranspiration.The aridity index is higher in the northwest,and the lower aridity index is found in the south and northeast.Under the high carbon emission scenario,the aridity index increases,and the area with a large increase is mainly located in the northwest.From the temporal trend,areas where the aridity index significantly declines are mainly located in the Qinghai-Tibet Plateau Region,and the areas with significant upward trend are mainly in the southeast,northeast and northwest regions.In terms of seasonal differences,the summer is relatively humid.However,the aridity index also shows a clear upward trend with the passage of time,especially in the North China Plain.The calculation principle of SPEI is different with aridity index,but the results are similar in characterizing the drought change.As far as SPEI is concerned across the country,the degree of drought under RCP 8.5 has increased significantly over time.The TFPW-MK test of the 12-month SPEI shows that the spatial variation of SPEI trends under different scenarios is obvious.Among them,area with significant upward trend of the SPEI under RCP 4.5 is the largest,which is more humid than other scenarios.(3)In the long run,the amount of water resources under RCP 4.5 is the most abundant.The available precipitation(the difference between precipitation and evapotranspiration)shows a decreasing trend from southeast to northwest.For the national average,the available precipitation is the highest under RCP 2.6 and 4.5 scenarios,and the least under RCP 6.0.From the temporal trend,the available precipitation under RCP 4.5 has an even growth rate,and it is the scenario with the most available precipitation until 2090 s.The potential annual runoff varies greatly among different river basins.The Yangtze River Basin,the Pearl River Basin and the Yarlung Zangbo River Basin have a relatively large annual runoff,and the annual runoff of the Northwest River Basin is relatively small.The annual runoff is slightly different under different RCP scenarios.On the whole,the average annual runoff is the most under RCP 4.5,and the change of annual runoff is more balanced in spatial distribution.The water resources are relatively abundant under this scenario.From the 14 watersheds crossed by the “Hongqi River”,the average annual runoff shows an increasing trend under the four RCP scenarios,among which the RCP 4.5 and 8.5 scenarios have the greatest increase after 2060 s.(4)There are “partial breakthroughs” in Hu' line locking the potential agricultural productivity.Under the RCP 4.5 and 8.5 scenarios,the potential agricultural productivity in the 2060 s changes obviously due to the changes of water resources and temperature.The Hu's line still locks the Chinese agriculture;however,partial breakthroughs exist,mainly in the eastern Tibet,western Sichuan,northern Hebei,and the northwestern region of Inner Mongolia.