Combined InSAR and optical dataset unravelling the characteristics of hillslope erosion in burned areas in Xichang, China

Wildfires often exacerbate hillslope erosion and lead to severe secondary disasters. Accurate monitoring of postfire hillslope erosion is crucial for land managers. However, current monitoring methods in burned areas are often time and capital intensive, posing challenges for large-scale and long-term observations. This study explores the potential of using multi-source data, including field investigations, optical remote sensing interpretation, and Interferometric Synthetic Aperture Radar (InSAR), to accurately estimate post-fire hillslope erosion. Particularly, quantitative analysis of C-band Sentinel-1 SAR data acquired one year before and three years after fire unraveled ground deformation in the areas burned on March 30, 2020, in Southwest China. Results show that in the first year following the wildfire, vegetation recovered rapidly, however, complete restoration to pre-fire levels requires more than three years. Hillslope erosion was found to be closely correlated with vegetation regeneration, peaking in the first post-fire year and declining as vegetation recovered. Nevertheless, it did not return to pre-fire levels within our observation period, indicating a recovery duration of over three years. Moreover, significant hillslope erosion variations were observed even within the same rainy season, with higher erosion rates during the early stages of rainfall, followed by stabilization in the later stages. Despite certain limitations associated with InSAR technology in burned areas, its potential for monitoring hillslope erosion presents a promising research approach for monitoring and modelling.