Soil Erosion Models at Regional and Watershed Scale Comparing SWAT, AnnAGNPS, PESERA, and RUSLE2015

In this study, the simulations generated by two of the most used hydrological watershed-scale models, the Soil and Water Assessment Tool (SWAT) and the Annualized Agricultural Non-Point Source (AnnAGNPS), were compared in a Mediterranean watershed, the Carapelle, located in Apulia, Southern Italy. Firstly, the models were built up using the same dataset. Afterward, they were calibrated and validated for runoff and sediment load at monthly scale, using a daily measured dataset (from January 2007 to December 2011). Three statistical indices (NSE, PBIAS, and R2) were used to evaluate model performance. Both models showed from satisfactory to very good correlation between observed and simulated streamflow and sediment load data. In the driest year, the specific measured sediment load at the outlet was 0.89 t ha−1 yr−1, while the simulated values were 0.83 t ha−1 yr−1 and 1.99 t ha−1 yr−1 for SWAT and AnnAGNPS, respectively. In the wettest year, the specific measured sediment load was 7.45 t ha−1 yr−1, and the simulated values were 8.27 t ha−1 yr−1 and 6.23 t ha−1 yr−1 for SWAT and AnnAGNPS, respectively. The study of the sediment source areas revealed that most of the basin is under moderate (1.4–10 t ha−1 yr−1) and high erosion risk (> 10 t ha−1 yr−1). The sediment yield predicted by the SWAT and AnnAGNPS models were compared with soil erosion estimates from the European scale models PESERA and RUSLE2015. The average gross erosion estimated by the RUSLE2015 model resulted comparable with the average specific sediment yield estimated by SWAT and AnnAGNPS, while the average soil erosion estimated by PESERA was lower than the other estimates. The methodology here applied could be considered an indirect method to calibrate or validate models applied at different scales, thus giving a measure of the uncertainty affecting the results.