Recharge estimation and soil moisture dynamics in a Mediterranean, semi-arid karst region

摘要

Knowledge of soil moisture dynamics in the unsaturated soil zone providesvaluable information on the temporal and spatial variability of groundwaterrecharge. This is especially true for the Mediterranean region, where asubstantial fraction of long-term groundwater recharge is expected to occurduring high magnitude precipitation events of above-average wet winters. Toelucidate process understanding of infiltration processes during theseextreme events, a monitoring network of precipitation gauges, meteorologicalstations, and soil moisture plots was installed in an area with a steepclimatic gradient in the Jordan Valley region. In three soil moisture plots,Hydrus-1D was used to simulate water movement in the unsaturated soil zonewith soil hydraulic parameters estimated by the Shuffled Complex EvolutionMetropolis algorithm. To generalize our results, we modified soil depth andrainfall input to simulate the effect of the pronounced climatic gradient andsoil depth variability on percolation fluxes and applied the calibrated modelto a time series with 62 years of meteorological data.Soil moisture measurements showed a pronounced seasonality and suggestedrapid infiltration during heavy rainstorms. Hydrus-1D successfully simulatedshort and long-term soil moisture patterns, with the majority of simulateddeep percolation occurring during a few intensive rainfall events.Temperature drops in a nearby groundwater well were observed synchronouslywith simulated percolation pulses, indicating rapid groundwater rechargemechanisms. The 62-year model run yielded annual percolation fluxes of up to66% of precipitation depths during wet years and of 0% during dryyears. Furthermore, a dependence of recharge on the temporal rainfalldistribution could be shown. Strong correlations between depth of rechargeand soil depth were also observed.