Analysis and Evaluation of Extreme Precipitation Events over the Qinghai-Xizang Plateau

To explore the interannual variability and spatial distribution of extreme precipitation events on the Qinghai-Xizang Plateau, this study employs percentile threshold methods to determine extreme precipitation thresholds based on three-hourly weather data from 215 meteorological stations on the Qinghai-Xizang Plateau. Additionally, extreme precipitation indices are calculated, and their spatial distribution characteristics are investigated. The main findings are as follows: 1) From 2005-2020, the annual precipitation on the Qinghai-Xizang Plateau exhibited an upward trend, with the Mann-Kendall trend test indicating a significance level greater than 99%. Notably, around 2017, there was a significant abrupt change in the annual average precipitation, showing a decreasing trend from southeast to northwest in spatial distribution. The monthly average precipitation on the Qinghai-Xizang Plateau ranged from 1.86 to 72.86 mm, with the highest monthly average precipitation occurring in July and the lowest in December. Seasonal precipitation characteristics were similar to those of the monthly averages, with the highest precipitation in summer and the lowest in winter. 2) The extreme precipitation threshold values at stations on the Qinghai-Xizang Plateau ranged from 4.81 to 41.26 mm, with an average of 14.96 mm. The spatial distribution of these thresholds resembled that of annual precipitation, decreasing from southeast to northwest. The highest extreme precipitation threshold was observed in Liangshan Yi Autonomous Prefecture, while the lowest was near the Qandam Basin. 3) From 2005 to 2020, extreme precipitation amounts, extreme precipitation days, and extreme precipitation intensities at all stations on the Qinghai-Xizang Plateau showed upward trends, but the extreme precipitation contribution rate declined. This suggests that the frequency or intensity of non-extreme precipitation events (such as light or moderate rain) may be increasing, thus contributing more to the total precipitation. Although the Tarim Basin and Qilian Mountains did not exhibit high levels of extreme precipitation amounts or days, their extreme precipitation contribution rates were relatively high, indicating that precipitation in these regions tends to occur in extreme forms.