Hydrology under climate change in a temporary river system: Potential impact on water balance and flow regime

The potential impacts of future climate scenarios on water balance and flow regime are presented and discussed for a temporary river system in southern Italy. Different climate projections for the future (2030-2059) and the recent conditions (1980-2009) were investigated. A hydrological model (SWAT) was used to simulate water balance at the basin scale and streamflow in a number of river sections under various climate change scenarios, based on different combinations of global and regional models (GCMs and RCMs). The impact on water balance components was quantified at the basin and sub-basin levels as deviation from the baseline (1980-2009), and the flow regime alteration under changing climate was estimated using a number of hydrological indicators (IHA). An increase in mean temperature for all months between 0.5-2.4°C and a reduction in precipitation (by 4-7%) was predicted for the future. As a consequence, a decline of blue water (7-18%) and total water yield (11-28%) was estimated. Although the river type classification remains unvaried, the flow regime distinctly moves towards drier conditions and the divergence from the current status increases in future scenarios, especially for those reaches classified as I-D (i.e. Intermittent-Dry) and E (Ephemeral). Hydrological indicators showed a decrease in both high flow and low flow magnitudes for various time durations, an extension of the dry season and an exacerbation of extreme low flow conditions. A reduction of snowfall in the mountainous part of the basin and an increase in potential evapotranspiration was also estimated (4-4.4%). Finally, the paper analyses the implications of the climate change for river ecosystems and for River Basin Management Planning. The defined quantitative estimates of water balance alteration could support the identification of priorities that should be addressed in upcoming years to set water-saving actions.