Temporal and spatial evolution characteristics of slope erosion caused by forest fires in Xide County, Sichuan Province on May 7, 2020

The southwestern mountainous areas of Sichuan Province in China experience dry winters and springs, creating favorable conditions for frequent forest fires. Under rainy events, slopes in burned areas are highly prone to intensified soil erosion, significantly increasing the risk of post-fire debris flows. Understanding the spatiotemporal evolution characteristics of slope erosion in open flame burned areas is of great significance for the comprehensive prevention and control of post fire debris flow disasters. This study focused on the burnt area affected by the “5•7” forest fire in Houshan, Zhongba Village, Xide County, Liangshan Prefecture, Sichuan Province in 2020. Based on the modified general soil erosion equation RUSLE and sediment transport ratio model, the spatiotemporal evolution characteristics of slope erosion and post fire debris flow slope source dynamic reserves of the burnt area from 2019 to 2023 were analyzed. The results show that the average soil erosion modulus of the slope surface in the study area in 2019 and 2020 were 1175 t/(km²·a) and 17771 t/(km²·a), respectively. The dynamic reserves of slope material sources were 950 m³ and 13792 m³, respectively. Forest fires can cause a significant increase in soil erosion modulus and dynamic reserves of slope material sources in the burned areas of the study area, and the increase is positively correlated with fire intensity. Subsequently, as vegetation gradually recovers, the average soil erosion modulus and slope material source dynamic storage of the burnt area will also gradually decrease. By 2023, the slope soil erosion modulus will decrease to 3421 t/(km²·a), and the slope material source dynamic storage will decrease to 2 457 m³, still higher than the pre burnt level, indicating that the slope erosion of the burnt area has been affected for more than 3 years.