Water resource sensitivity from a Mediterranean perspective : Using a hydrological model to explore the combined impacts of climate and land-water management changes

Future water supplies will be affected by both climate change and altered land-water management. In the Mediterranean region, an expected warming and drying together with increased water withdrawal in key tourist destinations will put further pressure on already scarce water resources. In this study, a scenario analysis was conducted to explore the combined impacts of climate and land-water management changes in an 89 km2 watershed upstream of Navarino Environmental Observatory, southwestern Greece. A simple process-based hydrological model based on the Thornthwaite-Mather water balance procedure for the estimation of daily actual evapotranspiration and soil moisture was used to predict streamflow and storage fluxes. The model conceptualization includes two storage compartments, loosely representing a shallow and fast draining groundwater component (S1) and a deep and slowly draining component (S2) from where the irrigation water was assumed to be taken. These were calibrated assuming no change in the hydrologic system over the three years of available data (2009-2011). The scenario analysis included the IPCC’s A2 and B2 projections for 2071-2100 and two scenarios for land-water management change 1) the conversion of olive groves to golf courses and 2) an export of irrigation water to a hypothetical golf course located outside of the catchment boundaries. The model results indicated vulnerability to future climate change which could reduce streamflow and potentially lead to a draw-down of the water table. For example, even under the B2 scenario (the least dry of the climate change scenarios explored), model simulated storages will be reduced by 32-87% and the simulated streamflow by 28-86% of the current level through introduction of a golf course size representing only 1.5% of the catchment area (depending of course on season considered and golf course location). The hydrologic system would thus be altered from the current 2009-2011 state by future land-water management changes towards intensive irrigation ...