Rainfall-runoff relationships in a semiarid rangeland watershed in central Mexico, based on the CN-NRCS approach

Abstract

In the southern region of the State of Zacatecas, Mexico, soil characteristics and cover as well as inadequate management practices have caused the high runoff’s coefficients and soil losses. This study was carried in a small (46.8 ha) and partially instrumented rangeland watershed. The Climate, management, physiographic, and hydrological data base for the La Cruz rangeland watershed were used to determining a watershed’s curve number (CN) value and after with this information parameterize the TR-55 Model with the objective to compute runoff as a function of rainfall depth and hydrological conditions (different CN values). Rainfall-runoff analyses of the La Cruz basin data show a Standard CN hydrological response and a CN value was compute close to 83 using the least-squares procedure. The Nash–Sutcliffe efficiency index (EI) is recorded at 0.65 when runoff simulations was use CN = 80 (improve rangeland watershed condition) and 0.43 when were using CN = 83 (traditional or poor rangeland management). A theorical approach between local stoking rates and hydrological conditions (CN values to good, fair and poor soil cover) was development in order to explain the watershed derioration caused by poor rangeland management practices (overgrazing) at this location.