RUNOFF GENERATION IN ARID AND SEMI-ARID ZONES.

The study reported two main objectives: (1) to analyze the most important factors controlling runoff generation processes in semi-arid and arid areas. A deterministic approach is used, special attention is paid to the spatial variability of these factors over short distances and the effect of this variability on hydrological forecasting; and (2) to present a simulation model of overland flow generation on an arid limestone hillside. The model is tested against a record of natural flow events. The approach adopted obviously differs basically from that of hydraulic engineers, who are mainly interested in the probability that extreme events may occur. Any attempt to understand the factors controlling spatial variability must focus on medium to low magnitude events in which such variability can be more easily detected and analyzed. Refs.