Model signatures and aridity indices enhance the accuracy of water balance estimations in a data-scarce Eastern Mediterranean catchment

Study region: Wadi Faria catchment, Palestine.

Study focus: The upper part of the Faria catchment (139km²) is a typical semi-arid karst catchment in the Eastern Mediterranean, where, up to recently, data availability has hindered the accurate assessment of renewable water resources. Newly available six-year time-series of rainfall and runoff data, combined with thorough field campaigns, enabled the application of the distributed TRAIN-ZIN watershed model. The model was constrained using seven hydrological signatures derived from the available time-series. New hydrological insights for the region: We found that the mean annual actual evapotranspiration was about 70% of precipitation, recharge was about 30% and natural runoff (excluding baseflow) 1%. Aggregated model results also supported aridity indicators that show the presence of InfiltrationExcess (Hortonian) Overland Flow, as well as the importance of indirect groundwater recharge and evaporation from soil during dry months. In total, maximum annual water availability was of the same order of magnitude as actual demand estimates (23 MCM). However, high spatial and inter-annual variability, and the presence of karst features suggest that water resources in the region are highly vulnerable.