Temporal and Spatial Variation Characteristics of Flood Season Precipitation in Xizang from 1981 to 2020

Based on the measured monthly precipitations of 38 meteorological stations in Xizang from 1981 to 2020, the spatial and temporal characteristics of flood season precipitation(P₅₉) in recent 40 years were analyzed by using the linear trend estimation, correlation coefficients, dominance analysis, and five mutation tests such as Mann-Kendall and Cramer. The results show that: (1) The average P₅₉ of each station in Xizang showed a decreasing distribution from east to west. Compared with those in the period of 1981—2020, the average values of 84.2% stations were more in the period of 1991—2020, especially in Gêrzê. (2) The P₅₉ of 78.9% stations increased with a rate of 1.2~31.9 mm·10a⁻¹ over Xizang in the past 40 years, while the P₅₉ of 55.3% stations decreased at a rate of 0.6~42.2 mm·10a⁻¹ in the past 30 years (1991—2020). The altitude was the dominant factor of the change trend of P₅₉, the P₅₉ decreased in area below 3640 m, and increased in area above 4000 m. (3) In recent 40 years, the average P₅₉ of 38 stations increased by a rate of 10.2 mm·10a⁻¹ in Xizang, mainly in May and July. The P₅₉ showed decadal variation with a significant decrease in the 1980s, a significant increase in the 1990s, a slight decrease in the 2000s, and a normal in the 2010s. The P₅₉ showed a sudden climatic change from more to less around 2005. There was a significant period of about 3 a in flood season and monthly precipitation.