The fact and causes of warm-dry and warm-wet change since 1971 in HEXI corridor area of Gansu Province, China

Abstract

Based on daily precipitation data of 19 weather stations from 1971~2017 over the Hexi Corridor in Gansu, characteristics of three analytical elements (precipitation, rain days and precipitation intensity) were analyzed. Results show that precipitation in the whole Hexi Corridor increases significantly in the autumn, and the winter precipitation in the east of Jiuquan to Zhangye also increases significantly. Rainy days in summer decreases significantly, while increases significantly in autumn. The extreme events using the three analytical elements account for 56% in 2000s, showing a significant increase. It accounted only for 16%, 10%, and 18% in 1970s, 1980s and 1990s respectively. Seasonal variability of the extreme events is also significant, i.e., 70% in summer, 60% in autumn, 50% in spring and winter. The frequency of the three analytical extreme events since 2000s is about half of that since 1971.Potential causes of the interdecadal changes of summer and autumn precipitation in 1990s and 2000s were investigated. There are obvious interdecadal variation in 200 hPa and 500 hPa geopotential heights, as well as the 700 hPa relative humidity and specific humidity. This variation leads to more autumn precipitation and less summer precipitation in 2000s.