Comparative analysis of water vapor transport characteristics for two types of extreme rainstorm processes in the western Hexi Corridor

Abundant water vapor supply is a necessary condition for the occurrence and maintenance of rainstorms. The western Hexi Corridor is located in the deep arid area in the northwest inland of China, but extreme weather events have occurred frequently in recent years. In order to reveal the characteristics of water vapor transport in the extreme rainstorm in this region, this paper first selected 4 extreme rainstorm processes in the western Hexi Corridor from 2010 to 2024 by using the precipitation data of meteorological observation stations, ERA5 reanalysis data and GDAS (Global Data Assimilation System) data, and then compared and analyzed the circulation situation, water vapor transport and budget characteristics. Then, based on HYSPLIT mode to simulate and calculate the water vapor trajectory of rainstorms and the contribution of water vapor from different sources. Finally, the three-dimensional structure models of water vapor sources and paths of two kinds of extreme rainstorms in the western Hexi Corridor were established, and the sources and contribution rates of water vapor in each layer were determined.The results are as follows. (1) According to the circulation situation, there are two types for the 4 extreme rainstorms. The first is the low vortex type rainstorm, the 500 hPa height field high in the east and low in the west, and the low vortex in the north of the Qinghai Tibet Plateau is the main influence system. The second is the subtropical high marginal type rainstorm, the 500 hPa height field high in the south and low in the north, and the Western Pacific subtropical high is the main influence system. (2) The two types of rainstorms have west and south water vapor transport belts. The water vapor source of the west transport belt is the same, but the south transport belt is different. In the low vortex type rainstorm, the west of the lower layer has strong water vapor transport intensity, and the middle layer is dominated by the south. In the subtropical high marginal type rainstorm, the south of the lower layer has strong water vapor transport intensity, and the middle layer is dominated by the west. (3) In the two types of rainstorms, the proportion of the net input of water vapor in the lower layer to the net input of the whole layer is more than 60%. In the low vortex type rainstorm, the water vapor input is mainly the west and north boundaries of the low layer and the east boundary of the middle layer. In the subtropical high marginal type rainstorm, the water vapor input is mainly the east boundary of the low layer and the west boundary of the high layer. (4) The water vapor sources of low vortex type rainstorm at 500 hPa are mainly the northern Xinjiang, the east of Southwest and the Mediterranean sea (Black Sea), while water vapor sources of at 700 hPa are mainly in Central Asia (Caspian Sea) and the east of Southwest. The water vapor sources of the subtropical high marginal type rainstorm at 500 hPa are mainly from the Mediterranean sea, while water vapor sources at 700 hPa are mainly from South Asia and western South China.The results will help to understand the formation mechanism of extreme rainstorm in the western Hexi Corridor, and provide some reference for the rainstorm forecast in this area in the future.