Study of the rainfall-runoff process in the Andes region using a continuous distributed model

The Precordillera area of the Andes Mountains (Mendoza, Argentina) is affected by severe flash floods, caused by heavy rainfall events of short duration and high intensities. A, telemetric network, installed on a pilot zone since 1983, provided a set of about 150 rainfall events. In addition, about 50 hood events were recorded at the outlet of a 5.47 km(2) catchment. The distributed model Areal Non-point Source Watershed Environment Response Simulation was adapted to this catchment and applied continuously over the period 1983-1994. The year 1985 was used for calibration. The model was able to reproduce runoff volume with an efficiency of 0.6, and peak discharge with an efficiency of 0.46. The largest events were however underestimated, although the model was able to reproduce the sharp increases in streamflow registered by the sensor. Based on the assumption that the model had captured the catchment behaviour, it was used to determine the main processes involved in runoff generation. The combination of rainfall and soil variability, mainly associated with a quasi-impervious area in the middle of the catchment, was found to explain the rapid increases in streamflow. Vegetation, surface storage capacity, and initial soil moisture were also influential but with a much smaller magnitude than the combination of rainfall and soil variability. (C) 1999 Elsevier Science B.V. All rights reserved.