Daily Water Surplus Variability between the Mediterranean, Semi-Arid and Arid Climates

Water surplus in a water balance is the fraction of precipitation which does not evaporate and not stored in the soil and includes both surface runoff and deep percolation. The annual course of the distribution of days with water surplus was estimated by a simple water balance model, which combines daily rainfall data, pan evaporation and soil water properties. The model was run using available published daily rainfall series and pan evaporation from ten Israel Meteorological Service stations, representing various climatic regions of Israel and using 21 different soil depths to simulate different root zone depths. The calculated daily water surplus series enable to evaluate the probability and amount of water surplus on each day of the year. The model output can be used in various hydrological models and be applied to other regions with similar conditions, without any special adjustment and may serve as an important tool for planners. This information is crucial for evaluation of the timing of occurrence of geomorphological and hydrological processes which depend on water surplus in various seasons. The annual aggregation of the water balance components provides a general view of the hydrological conditions of the different stations. The probabilistic representation of the results enables a comparison among stations with different rainfall regimes and soil types.