Evaluation of Global and Regional Soil Maps in Flow Forecasting using SWAT Model (Talar Watershed, of Mazandaran Province)

In most developing countries soil georeferenced data is not yet available. The FAO prepared the global map through the Coordinated Global Soil Database. The aim of this study was to evaluate the required details of the regional map in comparison with the soil global map of Talar watershed using the SWAT model. In this model, climatic data of 2004-2017 were used to simulate runoff. The first two years were used as model warm-up period, 2005-2015 for calibration and 2016-2017 for model validation. Sensitivity and uncertainty analysis, was done in SWAT-CUP software with the help of SUFI-2 algorithm. The evaluation of the model was done using the coefficients of explanation (R2) and Nash-Sutcliffe (NSE) statistics. The available soil water capacity (SOL_AWC) parameter was determined as a sensitive parameter. Before calibration, 32.7% (global) and 29.3% (regional) precipitation was simulated as daily flow. After recalibration based on the regional soil map (NSE=0.56 and R2=0.74) and global (NSE=0.56 and R2=0.64) and in the verification stage according to the regional soil map (NSE=0.59 and R2=0.76) and global (NSE=0.62) and R2=0.75) was estimated. The results showed the acceptable performance of the model in flow simulation. Sub-basin 9 (deciduous forest) and 14 (summer pasture) had the lowest and highest share in runoff production, respectively. The regional map provided more reliable results. Although the additional information provided by the regional map, while changing the optimized parameters in the model, has no effect on the outflow of the basin, the results indicated that the regional soil map has no significant effect on the flow prediction, and if it is not available, the global soil map information can be used.