Abstract:Based on the climatological average daily maximum temperature of more than 2 400 observation stations of the National Meteorological Information Center, the soil moisture and evapotranspiration data of GLDAS 2.0/2.1, the reanalysis data of 500 hPa geopotential height and 925 hPa wind field of ERA5, the grid sudden drought index was defined. And on the basis of the analysis of the climate characteristics of flash drought and the spatial mode of empirical orthogonal expansion of abrupt drought index in China from April to September during 1979-2017, the regions with frequent flash droughts and high variability were determined, the identification criteria of regional flash drought events were given, and the evolution process was analyzed synthetically. Finally, the elements and circulation characteristics of typical cases were analyzed. Results show that flash droughts occur mostly in summer of southern China, and most frequently in July, especially in Hunan and Zhejiang, which are also the regions with the largest climate variability. Synthetic analysis shows that high temperature is the main driving factor of flash drought outbreak in the two regions: before the drought outbreak, the temperature and the evapotranspiration increases rapidly, and the soil moisture decreases significantly. Two flash drought events occurred in Hunan Province from June to July in 2013. Before the first drought, the 500 hPa geopotential height over Hunan increased rapidly, the abnormal downdraft resulted in the decreasing of precipitation and adiabatic warming, and the evapotranspiration increased with the increasing of temperature, all of which result in the decreasing of soil moisture. So this drought was driven by high temperature; in the early stage of the second drought, the Northwest Pacific subtropical high, which is obviously westward, northward and stable, enhanced the surface net solar radiation flux, maintained the high temperature due to the southerly airflow near the stratum, and the evapotranspiration changed with the precipitation. The drought was driven by the decreasing of precipitation, and the high temperature played a promoting role.