Multitemporal Monitoring of Land Degradation Risk Due to Soil Loss in a Fire-Prone Mediterranean Landscape Using Multi-decadal Landsat Imagery

Natural, as well as human-induced, landscape changes may have profound effects on soil-loss rates in Mediterranean countries. Knowledge of the spatial and temporal distribution of the erosion processes from 1984 to 2013 across the fire-prone island of Thassos was gained on the basis of a joint analysis of imagery received from three generations of Landsat satellites. Soil loss was modeled using the revised universal soil loss equation. With the exception of the crop management factor, which was estimated through the NDVI image series, rainfall erosivity, soil erodibility, and topographic factor, were compiled within a GIS environment and used for the production of the spatio-temporal erosion maps. We found some constant patterns regarding the spatial distribution of soil susceptibility to erosion, similar to the findings of plot scale studies in the Mediterranean, as well as major changes related to the temporal intensity of the process. With regard to the aspect, we found that the most erosion-prone areas diachronically were the south-facing slopes. The highest altitudinal zone was most at soil-loss risk, but this elevation zone occupies the smallest spatial extent compared to the others. We observed a major increase for all the elevation and aspect zones, as well for every watershed of the island, during 1984-1991, when Thassos experienced some catastrophic fires. Between 1984 and 2013, all but one the watersheds of the island experienced a severe increase in soil erosion, suggesting the need for prevention measures and restoration plans that specifically target the areas most vulnerable to degradation. Quantification of the soil loss over large areas and large time extents, can contribute to an understanding of the process, highlight drivers of change and assist in the implementation of erosion control measures and decision making.