Impact of soil hydrology on the hydrological recharge of karst regions – A model approach

Precipitation is a major natural control on the amount of karst groundwater resources. However, not all amount of precipitation in karst regions results in aquifer recharge, since evapotranspiration uses significant hydrological resources. We have developed a soil model that quantifies the recharge at different sites in Slovenia and Croatia. To characterize the regional climate variability, the selected locations have different thermal regimes and hydrological balances across the Dinarides. The implemented model assumes that actual evapotranspiration results from the potential evapotranspiration and the available soil water content. The same hydrological soil characteristics were assumed for all studied locations to isolate the impact of climate on the hydrological recharge. The input data to run the model at each site are the monthly values of precipitation and temperature, and the values of the field capacity and initial soil water content have to be specified. For each site, the model was run for a period of 15 years, from 1975 to 1989, when the global warming had still limited impact on the region. The model quantifies the amount of rain water that finally reaches the aquifer. In sites with a clear positive hydrological balance more than 50% of precipitation turns into hydrological recharge. However, in sites with a clear negative water balance only between 20 and 25% of precipitation turns into hydrological recharge. The model highlights how vulnerable are the groundwater resources in most Mediterranean karst regions to drought or rise in temperatures. In the context of the ongoing climate change, the model shows that a warming of 2ºC results in higher actual evapotranspiration rates and decreases on the hydrological recharge by 15-20% in Mediterranean sites and by 30% in sites with a continental climate. This model also forecasts the karst groundwater hydrological recharge as a result of different scenarios of climate change.