Spatio-temporal Distribution Characteristics of Summer Precipitation Duration in Northwest China

Based on the daily precipitation observation data of 208 rain-gauge stations in Northwest China from 1961 to 2020, we use the statistical analysis method, the Mann-Kendall test method, the probability analysis and the ensemble empirical mode decomposition to analyze the spatio-temporal variation characteristics of precipitation duration and the contribution of the precipitation with different durations to the total precipitation. At the same time, the characteristics of precipitation duration in different regions (westerly region, monsoon transition region and monsoon region) are compared. The results show that the frequency, annual total precipitation and annual averaged precipitation intensity of the precipitation processes in Northwest China present a decreasing trend before the 1990s, but an increasing trend after 1991. Especially, the increasing trend is more obvious in the south-central and eastern parts of Northwest China. The occurrence frequency, total precipitation and average precipitation intensity of the precipitation processes with different durations all increase spatially from northwest to southeast, and this distribution is consistent with that of the climate zones in China. The distribution of the stations with a precipitation-increasing trend is closely related to the topography. In the north of large terrains, most stations present an increasing trend in precipitation frequency, total precipitation and precipitation intensity. The precipitation process in Northwest China is dominated by one-day precipitation process (short-duration precipitation process), and the frequency of the precipitation processes lasting for 3 days or more (long-duration precipitation process) is the least, but its precipitation intensity is the strongest. In the westerly region, the frequency and precipitation of one-day precipitation processes occupy the largest proportion. In the monsoon region, the frequency and precipitation of the precipitation processes lasting for 3 days or more occupy the largest proportion. In the past 60 years, the frequency, total precipitation and precipitation intensity of one-day precipitation processes show an increasing trend in all the three regions, while the two-day precipitation processes has no obvious change. For the precipitation processes lasting for 3 days or more, there is no obvious change or slight decrease in different regions. In general, the summer precipitation in Northwest China has an increasing trend. The results of this study may provide further understanding on the warming-wetting trend over Northwest China.