The Analysis And Projection Of Dry And Wet Climate Change In Central Asia

In recent decades,with the continued warming of the global climate,extreme weather events occur frequently,among which serious losses are caused.One kind of prolonged event is drought.Therefore,the study of the causes,duration and effects of drought is a particularly important research direction in the study of climate change.This study takes drought as the research object,and the research area is Central Asia,and the following conclusions are drawn:Firstly,the spatial and temporal characteristics of drought in Central Asia were analyzed using the Standardized Precipitation Evapotranspiration index(SPEI)released by the Instituto Pirenaico de Ecología,Spanish National Research Council.The results show that,on the whole,drought in Central Asia mainly occurred in 1975 and 1996.Kazakhstan experienced a relatively period of drought in the mid-1970 s and late 1990 s.Tajikistan shows a wet situation.The drought index reached-1.11 in 1971,which is a moderate drought.In 1969,the drought index reached 1.94,which is a serious humidity.Kyrgyzstan shows alternating wet and dry conditions.In the early1960 s,the mid-1970 s,the early 1980 s,the late 1990 s,and 2007 and 2008,there was a slight drought trend.The wetter years were the late 1960 s,the late 1980 s and the early21 st century.Both the drought index of Turkmenistan and that of Uzbekistan showed a downward trend,and the drought mainly occurred in the mid and late 1990 s.Secondly,from the monthly distribution of SPEI in Central Asia from 1961 to 2015,it can be seen that the Central Asia was relatively humid from 1960 s to early 1970 s.Drought began to appear in April 1975,and the degree of drought was light.The degree of drought intensified from May to August,reaching mid-drought.The degree of drought in September reached serious drought.The SPEI value was-1.53.The drought alleviated in October from severe to moderate.This moderate drought event lasted until April 1976.It lasted 12 months.The severity of drought and the durationof drought were rare in Central Asia in recent 55 years.Finally,the change of drought area coverage in Central Asia in the past 55 years was analyzed.The drought area coverage in Central Asia was below 22% from 1960 s to early 1970 s.In 1975,the drought area coverage in Central Asia was the highest,reaching 60.7%.From the1980 s to the early 1990 s,the drought area coverage remained below 30%.From the late 1990 s to the early 21 st century,the drought area coverage in Central Asia was relatively high.The large-scale atmospheric circulation anomaly often leads to the occurrence of drought.Therefore,in this study,Empirical Orthogonal Function(EOF)was used to analyze the main modes of dry and wet changes in 55 a in Central Asia,as well as the large-scale atmospheric circulation background corresponding to each mode.The results show that: the first spatial mode shows the reverse change of the middle and the north and south in CA.The central and western regions is high value center of drought-wet change.This spatial pattern corresponds to the existence of obvious zonal wave train in the middle and high latitudes.The pressure over the north Pacific and eastern Europe and western Asia is unusually low.The pressure on the west coast of Europe and the south of Lake Baikal is unusually high.The 500 hPa geopotential height field shows an obvious Eurasian-Pacific teleconnection pattern,indicating that the Lake Baikal blocking high is active.Therefore,the Eurasian Pacific telecorrelation may be an important circulation factor for the dry-wet change in Central Asia.The second main mode is the spatial pattern of north-south opposite changes.The distribution of dry and wet type may be influenced by the arctic oscillation.Global climate models are important tools for predicting future global climate change.After analyzing the evolution of dry and wet in Central Asia for nearly half a century,the global climate model is used to estimate the future dry and wet trends in Central Asia.In this study,the 21 global climate models were used,and the standardized precipitation index(SPI)and the standardized precipitation evapotranspiration index(SPEI)were calculated by using the method of multi-modelensemble.Different drought indexes were used to predict the future dry and wet variation trends in Central Asia under the scenario of RCP 4.5.The results show that under the background of global warming in the future,the trend of dryness in Central Asia will continue,especially in the desert areas of Uzbekistan and Turkmenistan.The future drought frequency of Central Asia calculated based on SPI1 and SPI3 will decrease,and the drought frequency of SPI12 will first decrease and then increase in the future.The drought frequency based on SPEI1,SPEI3 and SPEI12 decreased in the early period and increased in the middle and late period.