Analysis of precipitation evolution in critical region from lower Jinsha River to upper Three Gorges Basin

This study systematically analyzes the precipitation variations of the Yalong River Basin (YRB), lower Jinsha River (LJR), and upper Yangtze mainstream (UYM). Using methods including regression analysis, Mann-Kendall tests, power spectrum analysis, and composite analysis, we focusing on the annual period, main flood season, reservoir impoundment period, and key drawdown period four temporal scales. The results indicate a significant increase in annual and drawdown-period precipitation in the YRB. In contrast, the LJR and UYM exhibited decreasing trends across all temporal scales. Periodicity analysis revealed a 5-year cycle during the flood season and a 13-year cycle during the impoundment period in the YRB. A 3-year cycle was identified during the impoundment period in the LJR, while the UYM showed 3-year cycles in both the flood season and drawdown periods. Composite analysis of rainstorm events revealed a typical pattern that precipitation generally began as moderate rain one day earlier in the northwestern Jialing River and Minjiang River Basin, then intensified and extended eastward and southward toward the upper mainstream as heavy rain, and weakened back to moderate rain in the Three Gorges area and finally exiting the region.