Water balance estimation under the challenge of data scarcity in a hyper-arid to Mediterranean region

Water budget analyses are important for the evaluation of the water resources in semi-arid and arid regions. The lack of observed data is the major obstacle for hydrological modelling in arid regions. The aim of this study is the analysis and calculation of the natural water resources of the Western Dead Sea subsurface catchment, one which is highly sensitive to rainfall resulting in highly variable temporal and spatial groundwater recharge. We focus on the subsurface catchment and subsequently apply the findings to a large-scale groundwater flow model to estimate the groundwater discharge to the Dead Sea. We apply a semi-distributed hydrological model (J2000g), originally developed for the Mediterranean, to the hyper-arid region of the Western Dead Sea catchment, where runoff data and meteorological records are sparsely available. The challenge is to simulate the water budget, where the localized nature of extreme rainstorms together with sparse runoff data results in few observed runoff and recharge events. To overcome the scarcity of climate input data we enhance the database with mean monthly rainfall data. The rainfall data of two satellites are shown to be unsuitable to fill the missing rainfall data due to underrepresentation of the steep hydrological gradient and temporal resolution. Hydrological models need to be calibrated against measured values, hence the absence of adequate data can be problematic. Therefore, our calibration approach is based on a nested strategy of diverse observations. We calculate a direct surface runoff of the Western Dead Sea surface area (1801 km2) of 3.4 mm/a and an average recharge (36.7 mm/a) for the 3816 km2 subsurface drainage basin of the Cretaceous aquifer system.