Positive rainfall erosivity trends compared with the reduction in soil erosion in a Mediterranean area (1996–2020)

Abstract

This work describes a procedure that uses the regression line slope to calculate the time trend of any variable in a raster image with ArcGIS Pro Geographic Information System (GIS) tools. The procedure is applied to estimated mean soil erosion and mean annual rainfall erosivity in the Andalusian territory (Spain) using data from the regional environmental agency. During the analyzed period (1996-2020), soil erosion values (RUSLE) show a region affected by low and medium estimated erosion values (91.74% of the territory between 0 and 50 t·ha-1·yr-1) and a large part by low to very low rainfall erosivity rates (70.43% of the territory between 132 and 1000 MJ·mm·ha-1·h-1·yr-1). The highest values for both parameters are limited to the mountain areas of the Baetic and Sierra Morena ranges. Estimated mean erosion presents a general downward trend, with 92.64% of the territory with slopes between 0 and -344 t·ha-1·yr-1 per year. Nevertheless, mountainous enclaves stand out for a positive trend in this parameter during the analyzed period, with regression line slope values of up to +5 t·ha-1·yr-1 (7% of the region, 6131.79 ha). The observed rainfall erosivity time trend shows that a combination of high rainfall erosivity rates and a strong upward trend is only found in the western extreme of the Baetic mountain ranges. Analysis of mean distribution by subwatershed has been verified to allow the competent environmental agencies to read the results more easily to address the erosion problem. The combination of mean estimated erosion values and the upward erosion trend in the Guadalete, Guadalhorce, and Verde subwatersheds helps guide actions in these areas.