Spatiotemporal patterns and drivers of soil erosion in Yunnan, Southwest China: RULSE assessments for recent 30 years and future predictions based on CMIP6

Soil erosion is a critical driving force of regional-scale ecosystem dynamics. Quantifying soil erosion and its responses to climate and land cover changes comprise an important part of regional ecological security assessment. Taking account of rainfall and vegetation cover changes in Yunnan Province, Southwest China, from 1986 to 2015, this study explored the spatiotemporal patterns of soil erosion intensity in Yunnan over this 30-year period, using the Revised Universal Soil Loss Equation. Sensitivity analyses were performed to evaluate the roles of rainfall (R) and vegetation cover (C) changes in soil erosion. Based on the climate model CMIP6, the carbon emission socio-economic sharing scenarios SSP126 and SSP585 were compared, using a random forest model, to predict soil erosion risk in Yunnan in different future periods. The results indicated the following: (1) During 1986-2015, soil erosion was detected in 33.55% of the land area of Yunnan, among which the areas of slight, moderate, severe, very severe, and extremely severe erosion accounted for 19.55%, 7.64%, 3.23%, 2.08%, and 1.04%, respectively; the 30-year mean annual soil erosion modulus over Yunnan was 1289.72 t km-2 a-1. (2) The area percentage change of five soil erosion intensity levels consistently showed a generally declining trend of soil erosion during the 30-year period. Comparing 1995-2006 vs. 1986-1995 and 2006-2015 vs. 1996-2005, area percentages were 1.56% and 2.4% for intensively reduced, respectively, and correspondingly 16.65% and 22.12% for reduced, 68.11% and 71.15% for no significant change, 12.79% and 4.02% for enhanced, and 0.08% and 0.03% for intensively enhanced. (3) Factor C was a more sensitive driver than R for soil erosion in this period. (4) Under the SSP126 and SSP585 scenarios, soil erosion risk was predicted to rise in the 21st century; and the provincial average soil erosion risk was larger for the SSP585 than the SSP126 scenario. Compared with the average of the 30-year period, predicted soil erosion in the SSP585 and SSP126 scenarios in 2100 would increase in western and southern Yunnan, while the SSP585 scenario predicted more severe soil erosion in southern and southwestern regions than SSP126. Our historical assessments and future forecasts suggest vegetation protection in karst areas and restoration in southern Yunnan will be critical for future soil erosion control and regional ecological security in Yunnan.