Impact Assessment Of Future Climate Change On Global Drought Propensity And Grain Crop Water Demand

Under the background of global warming,the increase in air temperature will affect several water cycle processes,such as precipitation,snow melting,and evapotranspiration,which threatens the water resource balance in some regions and changes the spatiotemporal characteristics of drought.As a high-water-consuming industry,the agriculture water use accounts for more than 70% of global water use.Climate change accelerates the regional water cycle and poses certain threats to agricultural water security.How to solve the contradiction between high agricultural water demand and limited available freshwater and alleviate the negative impact of climate change on them have become the priority of agricultural water management.Quantitative evaluation of how future climate change will affect drought and agricultural water use is essential to reveal the evolution of drought under future climate scenarios,alleviate water pressure,and ensure regional agricultural water use security and food security.In this case,this study firstly coupled 22 Global Climate Models to interpret the spatiotemporal evolution of major meteorological factors during 2020–2089 and further explored the global drought propensity under climate change based on the Standardized Precipitation Evapotranspiration Index.Secondly,through combining the Global Land Data Assimilation System database and the global crop database,this study evaluated the evolution characteristics of evapotranspiration under future climate scenarios at the scale of the globe and planting areas of main crops.Finally,this study evaluated the influence of climate change on drought and agricultural water use in main grain-producing countries,to provide theoretical support for global and regional strategy to combat climate change and drought and manage agricultural water use.The main conclusions of this study are as follows:(1)There exist obvious spatial differences in meteorological factors,including air temperature,solar radiation,wind speed and precipitation,and drought in future climate scenarios.Under two future climate scenarios(Representative Concentration Pathway RCP4.5and RCP8.5),the average annual temperature in most parts of the world shows a significant upward trend.The annual and seasonal variation trends of wind speed,solar radiation,specific humidity,and precipitation have similar spatial distribution patterns,and the trend is more significant under RCP8.5 scenario.Mann-Kendall trend test indicates that northern and southwestern Africa and western Asia will experience significant intensifying drought under two climate scenarios.Empirical Orthogonal Function analysis shows that during 2020-2089,drought will be detected for more than half of the period in northern Africa and western Asia under RCP4.5 scenario and in northeastern Africa under RCP8.5 scenario.(2)Under future climate scenarios,the annual evapotranspiration near the equator is relatively higher,and the annual evapotranspiration in the Northern Hemisphere is generally on the rise while that in the Southern Hemisphere is generally on the decline.In addition,the annual and seasonal trend of evapotranspiration have similar spatial pattern,but the trend is more significant under RCP8.5 scenario.The crop water demand of irrigated wheat and maize will increase significantly in western Europe,central North America,and eastern Asia.The irrigation water demand during the growth period of irrigated wheat will increase significantly in southern Asia and northern Africa,but the corresponding area is smaller under RCP8.5scenario.The significant increase in irrigation water demand during the growth period of irrigated maize are detected in southern Asia and southwestern Europe.The main reason is that the changing trend of effective precipitation under RCP8.5 scenario is more significant,which further affects the regional irrigation water demand for crops.(3)The characteristics of drought occurrence in major grain producing countries and the effects of climate change on agricultural water use are revealed.Under future climate scenarios,China,the United States,India,and Brazil will face an overall intensification tendency of drought from 2020 to 2089 and the drought situation varies greater among different regions in Indonesia than in other countries.The difference of drought conditions in different regions within countries is greater under RCP8.5 scenario.The drought in the United States and Brazil will overall be intensified.In terms of effective precipitation,the annual effective precipitation in Indonesia is higher under two climate scenarios.The difference of annual effective precipitation in different regions of Russia is smaller than in other countries and the variation is quite consistent.Meanwhile,the annual effective precipitation will experience an obvious increase in Russia and a decrease in Indonesia and Brazil.Under two climate scenarios,the annual evapotranspiration in Indonesia and Brazil is relatively higher.The difference in annual evapotranspiration is smaller in different regions in Russia but larger in Brazil.In terms of evapotranspiration,the overall trend of annual evapotranspiration in Russia is obviously increasing.For Brazil and Indonesia,their overall evapotranspiration is relatively higher and they are also facing a decrease in effective precipitation,in which case future climate change poses certain threats to their domestic agricultural water use.