A methodology to use climate change information in water resources evaluation is developed through a meaningful case study in southern Italy (the Apulia region). The problem of the effective information of climate model simulations with respect to small scale impact studies is developed taking into account the limited predictive capability of climate models. Therefore downscaling and biascorrection requirements are treated through a specifi c methodology based on a quantile variable correction adopting ground based observation of climate variables. The meteorological forcing for the impact study are obtained through the downscaling of atmospheric variables produced by a Regional Climate Model (RCM) called Protheus. The impact assessment on the water balance of the Apulia region (southern Italy) revealed a marked increase in the variability of hydrologic regimes (both runoff and groundwater recharge) as consequence of the increased rainfall variability predicted for the twenty-fi rst century, while preserving a decreasing in the annual trend. Moreover, the analysis of climate change effects was performed focusing on the rainfall-discharge process of a strategic karst spring supplying the Apulia aqueduct. In this case study, no substantial variations in the annual mean discharge are recognized, although a marked decrease in the mean monthly discharge was found between October and December, which represent the start of the recharge period of Apennine aquifers. Such results represent a crucial water management issue that has to be addressed in terms of adaptation to meet future water resources requirements.