Abstract
Abstract. Knowledge of soil moisture dynamics in the unsaturated soil zone provides valuable information on the temporal and spatial variability of groundwater recharge. This is especially true for the Mediterranean region, where a substantial fraction of long-term groundwater recharge is expected to occur during high magnitude precipitation events of above-average wet winters. To elucidate process understanding of infiltration processes during these extreme events, a monitoring network of precipitation gauges, meteorological stations, and soil moisture plots was installed in an area with a steep climatic gradient in the Jordan Valley region. In three soil moisture plots, Hydrus-1D was used to simulate water movement in the unsaturated soil zone with soil hydraulic parameters estimated by the Shuffled Complex Evolution Metropolis algorithm. To generalize our results, we modified soil depth and rainfall input to simulate the effect of the pronounced climatic gradient and soil depth variability on percolation fluxes and applied the calibrated model to a time series with 62 years of meteorological data. Soil moisture measurements showed a pronounced seasonality and suggested rapid infiltration during heavy rainstorms. Hydrus-1D successfully simulated short and long-term soil moisture patterns, with the majority of simulated deep percolation occurring during a few intensive rainfall events. Temperature drops in a nearby groundwater well were observed synchronously with simulated percolation pulses, indicating rapid groundwater recharge mechanisms. The 62-year model run yielded annual percolation fluxes of up to 66% of precipitation depths during wet years and of 0% during dry years. Furthermore, a dependence of recharge on the temporal rainfall distribution could be shown. Strong correlations between depth of recharge and soil depth were also observed.
Highlights
In the Mediterranean region, groundwater is the main source for domestic and agricultural water supplies (EUWI, 2007)
To extrapolate our point measurements of soil water balance, we varied soil depth and climatic input parameters over ranges observed in our study area
We showed that point measurements of soil moisture together with numerical modelling of the water flow in the unsaturated soil zone may help to understand dominant percolation mechanisms
Summary
In the Mediterranean region, groundwater is the main source for domestic and agricultural water supplies (EUWI, 2007). Knowledge on the quantity of groundwater recharge is a prerequisite for sustainable water resources planning and effective water use. Karst areas are important in this respect, because during high intensity winter storms precipitation may rapidly infiltrate into exposed karst surfaces and induce high recharge rates (De Vries and Simmers, 2002), which are common in the Mediterranean area (Ford and Williams, 2007). A rapidly increasing water demand in the last decades has led to a widespread overexploitation of groundwater resources (EUWI, 2007). The Mediterranean region has been identified as a “hotspot” of current and future climate change (Giorgi, 2006; IPCC, 2013), imposing additional pressure on its limited water resources. More insights into processes of aquifer replenishment in Mediterranean karst regions are of vital importance
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