Abstract

The curve number method by the Natural Resources Conservation Service of the United States was used to study the effect of land cover changes on runoff in the Lirquen River Basin, Chile. The curve number was calculated using two methods: (1) classification of three LandSat images from 1987, 2003 and 2009, in combination with soil texture information and correction for the effect of the slope, and (2) the use of the runoff coefficient from daily rainfall and flow data for the periods 1985-1988, 2001-2004 and 2007-2010. The first method resulted in CN values for 1987, 2003 and 2009 of 51, 46 and 49 respectively, since mature grassland areas changed over the same years from 27.9 to 15 and 17.7%, respectively. Furthermore, the adult plantation area changed over those years from 7.2 to 22.9 and 15.4%, respectively. The results from the second method show higher curve number values during the period 1985-1989 and lower numbers during the period 2001-2004, since the runoff volume generated over this period was smaller than the other two. This is due to an increase in the adult plantation area which provides greater intercept capacity, higher evapotranspiration rates and greater storage of soil moisture.