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

•The water balance of a semi-arid karst basin was studied with a distributed model.•The model was constrained with seven hydrological signatures.•On average, evapotranspiration is approximately 70% of annual rainfall, percolation 30%.•Aridity indicators reveal relationships between rainfall and hydrologic processes.•High spatial and temporal variability suggests high water resources vulnerability.

Study regionWadi Faria catchment, Palestine.Study focusThe upper part of the Faria catchment (139 km2) 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 regionWe 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 Infiltration Excess (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.