Hydrological model of the Sordo River watershed, Oaxaca, Mexico, using SWAT

The Sordo watershed is located in the western portion of the state of Oaxaca, Mexico. It drains an area of 7 751.42 km(2) and is predominantly a sedimentary basin with significant water erosion problems (50-200 t ha(-1)yr(-1)). The main goal of this work was to calibrate and validate the SWAT model (Soil and Water Assessment Tools) in order to establish parameters that are useful to hydrological evaluations and decision-making. To this end, 10 years of climate information were used (1975-1985) and physiological variables were defined for 13 vegetation covers. In addition, physical and chemical properties were determined for nine soil types found in the area. Based on elevation data, soil types, and vegetation cover, the basin was divided into 175 sub-basins and 1 729 hydrological response units. For calibration (c) and validation (v) purposes, the coefficient of determination (r(2)) and the Nash-Sutcliffe efficiency coefficient (NSE) were calculated for observed and simulated annual biomass yield (r(2) = 0.96 c and NSE = 0.95 c), monthly flow rates (r(2) = 0.84 c, NSE = 0.83 c, r(2) = 0.7 v, and NSE = 0.81 v), and monthly sediment loads (r(2) = 0.59 c, NSE = 0.51 c, r(2) = 0.58 v, and NSE = 0.45 v). In conclusion, the SWAT model was satisfactorily calibrated and validated, and it is recommended for decision-making related to soil conservation strategies in the Sordo River Basin in Oaxaca.