Spatiotemporal variations of precipitation-driven dry–wet boundaries and associated impacts from 1975 to 2025 in Mainland China

Climate change is accelerating the water cycle and shifting climatic boundaries, potentially challenging flood-control systems in northern China designed under historical climate stationarity. Yet, the spatiotemporal movement of core precipitation isohyets defining China’s dry–wet boundaries has not been fully quantified. Here we analyze data from 2474 meteorological stations across Mainland China during 1975–2025 to track changes in the 200-, 400-, and 800-mm isohyets and basin-scale precipitation patterns. We find significant wetting across the northern basins, contrasting with relative stability across the southern humid basins. After 1996 and 2011, respectively, the 200- and 400-mm boundaries shifted northwestward and westward, expanding relatively humid conditions across the northern basins. By contrast, the 800-mm humid boundary remained comparatively stable across Mainland China. Importantly, in the Haihe and Yellow River Basins, the post-2011 400-mm transition was more strongly associated with R50 (annual precipitation from rainstorm days) than with non-extreme precipitation. After the 2011 changepoint, rainstorm activity became increasingly concentrated in the northern transition band, accompanied by synchronous increases in regional heavy-rain frequency and intensity. The recent wetting of these basins thus includes a structural shift toward more concentrated rainstorm precipitation, with implications for regional flood risk management and water resources planning.