Influence of Typhoons in the Western Pacific on Summer Precipitation in the Eastern Northwest China

Based on the precipitation and typhoon data from 1970 to 2020 (42 years) and traditional statistical methods and random forest, this study investigated the influences of typhoons in the western Pacific on precipitation in the eastern Northwest China (33°N–45°N, 93°E–110°E, ENWC). The results revealed that the peak frequency values for typhoons and precipitation occur in July, August, and September. Typhoons in the western Pacific play an important role in the mean daily precipitation during the typhoon period (TP). The location and intensity of typhoons considerably influence the precipitation in July, and the location, intensity, and frequency of typhoons affect the precipitation in August, while typhoons have little influence on the precipitation in September. The typhoon influence changes with location, time, and precipitation level and is mainly in the second EOF pattern. Furthermore, the heavy and extremely heavy precipitations show that typhoons are not the main factors influencing TP, and their influence is indirect and nonlinear. Typhoons influence precipitation by affecting the location and intensity of the ridges and troughs in the mid-latitude, West Pacific subtropical high, and vortex in the low-latitudes. The random forest model can fit the distribution and intensity of precipitation better than the linear model, demonstrating that the typhoon influence on TP is mainly nonlinear and that influence increases with precipitation intensity. The random forest model also indicates that typhoon location is the most important factor influencing precipitation in the ENWC.