Abstract
Quantification of water balance components, under arid conditions, is essential to the development of water management policies. The application of the mass water balance approach for the assessment of water resources in a typical watershed located in the southwestern region of Saudi Arabia is demonstrated. The water balance approach was used, on an event basis, to express the amount of precipitation for 13 storms over a three-year period, as a percentage of other hydrological components such as runoff, evaporation, and recharge. The study indicated that 63 percent of precipitation is lost through evaporation from the water surface during flooding, and from the upper layers of the soil surface immediately after storms. Another 32 percent is stored in the form of soil moisture in the unsaturated layers below the effective evaporation depth. Only 3 percent of the precipitation was transformed into surface runoff; however, 75 percent of this contributes toward groundwater recharge. It is shown that a mass water balance approach can b used, with reasonable accuracy, to quantify the components of the hydrological processes under arid conditions, where a reliable data base is available. This, in turn, will help in the development of appropriate water management policies for arid regions. (Author 's abstract)