Evolution And Propagation Of Sudden Drought In Yunnan Provinc

The frequency,duration and severity of droughts in China under the background of climate warming have shown a significant upward trend.Therefore,improving the accuracy of drought monitoring and forecasting,establishing real-time drought early warning system,and enhancing the comprehensive response capability of drought prevention and combating has become a major scientific problem that needs to be solved in China’s economic development.This paper analyzes the climate change characteristics of Yunnan Province based on ERA5 reanalysis data in five aspects: temperature,precipitation,net radiation,evapotranspiration,and wet and dry conditions.Based on the standardized precipitation evapotranspiration index,we identify flash droughts,analyze the spatial and temporal characteristics and seasonal characteristics of flash droughts,and further investigate the meteorological causes of flash droughts.Based on the monthly standardized precipitation evapotranspiration index and the standardized runoff index,we identify meteorological drought and hydrological drought by means of the travel theory,and compare and analyze the propagation characteristics of meteorological drought and flash drought to hydrological drought,and the main conclusions are as follows:(1)The overall temperature in Yunnan shows an upward trend in all four seasons,and the upward trend is significant in most areas,and spatially,the temperature shows a step-wise increasing trend from northwest to southeast.There is a significant seasonal variability in precipitation,with a clear distinction between wet and dry seasons,more precipitation in summer and less in spring,and an overall significant downward trend.Net radiation is greater in spring and summer,with an overall significant upward trend in summer and autumn.There is a sudden change in climate from wet to dry at the beginning of the 21 st century,with an increasing trend of dryness.(2)Central and southern Yunnan are the areas with high incidence of flash droughts.On the whole,the frequency of flash droughts in Yunnan Province has a weak increasing trend,and the average duration of flash droughts has significantly decreased,indicating that the development of flash droughts has a tendency to accelerate.Flash droughts mainly occur in spring and winter,among which,the frequency of flash droughts in spring is higher and the duration of flash droughts in winter is longer.The abrupt droughts in Yunnan are mainly related to strong subsidence movements,with dispersion at lower levels and convergence at higher levels,and significant subsidence movements leading to abnormally low precipitation.(3)The drought propagation time in most of Yunnan is 1 month,through which the meteorological drought develops into a hydrological drought of greater intensity and longer duration.Flash droughts are more likely to propagate into hydrological droughts than meteorological droughts.Flash drought events of greater intensity or duration have a greater probability of developing into hydrologic droughts.