Extreme precipitation driven humidification in Northwest China: Changes in precipitation characteristics and atmospheric water vapor transport in Northwest China, 1961-2020

Northwest China is a typical arid and semi-arid region and an important climate-sensitive and vulnerable area. In recent decades, this region has experienced a notable trend toward humidification. Understanding the characteristics and trends of precipitation and the atmospheric water vapor cycle in this area is essential for predicting the future evolution of this phenomenon. Using observational and reanalysis data, this study classified precipitation in Northwest China from 1961 to 2020 into 20 levels, ranging from light to heavy events. The analysis shows that the overall increase in precipitation is largely driven by extreme precipitation events exceeding the 90th percentile, with the rising frequency of heavy precipitation accounting for most of the observed changes. Precipitation intensity across different levels is positively correlated with both external moisture transport and regional moisture contributions. Heavy precipitation events are closely linked to stronger moisture inflows and more active regional recycling processes. Enhanced precipitation efficiency and shorter moisture residence times further facilitate the occurrence of intense precipitation in the region. The increasing trend in heavy precipitation is primarily associated with greater moisture contributions from cross-equatorial flows over the Indian Ocean and increased local evaporation. These factors enhance land-atmosphere interactions and precipitation efficiency, thereby driving the frequency and intensity of extreme precipitation events.