Water Vapor Characteristics of Summer Drought and Flood and Typical Rainstorm in Hexi Corridor

Water vapor source and transport path are main factors of affecting drought-flood mode in Hexi region of China， and also key factors to be considered in the rainstorm forecast in this region.Using conventional observations and ERA-Interim reanalysis data from 1979 to 2019， the differences of water vapor transport characteristics of summer typical rainstorms in different circulation conditions and the average climate state of water vapor transport in drought-flood years were comparatively analyzed in Hexi Corridor.The results showed that： （1） The summer standardized precipitation index SPI and the whole layer water vapor flux showed a slightly more dry trend， with change tendency rate of -0.04·（10a）-1 and -5.7 kg·（m·s）-1·（10a）-1， respectively.（2）The main sources of summer water vapor were northwest （Arctic Ocean） and west （Black Sea and Caspian Sea）， among which the drought year was from northwest whose water vapor flux was less than 50 kg·m-1·s-1， the flood year was from west whose water vapor flux was 50~100 kg·m-1·s-1； in drought-flood years， the water vapor input was mainly from boundaries of west and north， and all regional water vapor expenditure was net outflow.（3） Both of two typical rainstorms had water vapor transport along west road， which was consistent with climate average state of summer flood years， but the water vapor supplement and confluence of other paths in the middle and low atmosphere layers were still needed which formed strong water vapor flux convergence， the regional water vapor income and expenditure was a net inflow， the water vapor of low trough rainstorm on northwest side of the Western Pacific Ocean subtropical high was mainly from west road of Caspian Sea and Black Sea， south road of South China Sea and southwest road of the Bay of Bengal， whose maximum center of water vapor flux was 100~150 kg·m-1·s-1， the water vapor input was mainly from south boundary and west boundary； the water vapor of rainstorm in Hetao block high was from east road of Bohai Sea， west road of Caspian Sea and Black Sea， southwest road of the Bay of Bengal， the above three water vapors were conveyed by relay type to the rainstorm area， whose maximum center of water vapor flux was up to 250~300 kg·m-1·s-1， the water vapor input was mainly from boundaries of east and south.