Runoff patterns in the Lechuguilla-Ohuira-Navachiste watershed, Sinaloa , , associated with changes in land use: An approach to the curve number model [Patrones de escurrimiento en la Cuenca Lechuguilla-Ohuira-Navachiste, Sinaloa, asociados a cambios de uso del suelo: Una aproximaci�n con el modelo del n�mero de curva]

In order to analyze trends in land use change in the Lechuguilla-Ohuira-Navachiste watershed (Sinaloa), as well as their impact on runoff patterns, a geographic information system (GIS) was integrated with land use/cover thematic maps, soil cartography and rainfall time-series. Land use/cover thematic maps, with accuracies > 85%, were produced by supervised classification of Landsat satellite imagery (1973, 1986, and 2000). Agriculture was the main land use during the study period, covering between 34% and 45% of the basin area. At the landscape level, changes amounted to 33% from 1973 to 1986, and 27% from 1986 to 2000, mainly associated with shrub vegetation and agriculture classes, which changed at mean annual rates of 2.1% and 0.6%, respectively, from 1973 to 2000. To evaluate the impact of landscape changes on the watershed runoff, the curve number model was used, obtaining mean annual runoff volume estimates of 198 � 106 m3 in 1973, 302 � 106 m3 in 1986 and 197 � 106 m3 in 2000. Those volumes correspond to runoff coefficients of 16%, 20%, and 23%, respectively. The results indicate that changes in runoff volumes in the study area depend more on the variation of precipitation rates than those observed in land uses and cover changes, because of the high proportion of fine-textured soils, with little infiltration rates and runoff potential resistant to changes in land use