A decline in soil erosion modulus occurred widely in Southwest China since the 1960s

To assess the long-term sustainability of soil retention in erosion-prone karst regions, investigating historical soil erosion process and their mechanisms in southwestern China, a typical karst-dominated region, are essential. While soil erosion processes have been studied in Southwest China over the last ~60 years, longer-term records remain rare. Here, we examined soil erosion processes over the past ~250 years in Chongqing Municipality, located in northern Southwest China, utilizing 137 Cs, 210 Pb, and AMS 14 C dating on sediments profiles from two karst depressions. These results were compared with published soil erosion modulus data to understand spatial changes in Southwest China. The results exhibited high soil erosion modulus from ~1750s to ~1935–1945 AD at both depressions, relating to the Hu-Guang Fills Sichuan Migration, Zea mays cultivation expansion, and elevated precipitation. Erosion modulus declined after ~1935–1945 AD likely due to wartime impacts. Slight soil erosion peaks appeared during ~1950–1960 AD, linked to the Great Leap Forward and the Great Steel Campaign. From ~1960s to 2018 AD, long-term soil erosion declines occurred. By compiling published data in Southwest China, we found widespread decline in soil erosion modulus during this period. We attribute this to reduced erodible soil stocks due to earlier severe erosion, combined with large-scale ecological restoration projects implemented since the 1990s. This study provides scientific bases for improving sustainability of karst ecological restoration projects.