Climate-change potential effects on the hydrological regime of freshwater springs in the Italian Northern Apennines.

In large areas of the Italian Northern Apennines, hundreds of low-yield springs provide water for drinking and industrial purposes, with short groundwater flow paths being formed within fractured sedimentary rock units. This hydrogeological setting results in spring water discharges that closely follow meteoric water recharge patterns, leading to low-flow periods concentrated in the summer/early autumn. Therefore, the springs' outflow can be very sensitive to a shortage in water recharge, as it was the case in 2003 and 2017, when a prolonged period of drought caused severe water management issues. This work analyses how a group of such springs responds to climate change. In particular, we first validated a hydrological rainfall-runoff model on the basis of daily discharge data collected between 2013 and 2016. Then, outflows were simulated for baseline (1984-2013) and future periods (2021-2050) using weather data provided by five RCM-GCM combinations. Finally, we performed statistical analyses aiming to examine the intra-annual variability in discharge rates, low-flow indices, flow-duration curves and the length of low-flows. Results show no evidence of change in mean annual discharges, but future climate estimates suggest a slight change to seasonal discharges in the future, with a marked increase of discharge during winter and spring, and a decrease in summer and autumn. Q(95) and 7Q10 low-flow indices (i.e. the daily discharge exceeded 95% of the time and the minimum weekly discharge associated with a 10-year recurrence interval, respectively) are significantly affected by the climate change (-21.8% and -25.0%, respectively), while droughts are expected to be more frequent: the number of years with a consecutive low-flow between 51 and 100days to increase by a third, and between 101 and 150 to duplicate.