Understanding future hydrologic challenges: Modelling the impact of climate change on river runoff in central Italy

Central Italy's diverse ecosystems and landscapes are susceptible to the Mediterranean climate change, affecting water resources and riverine systems. Managing these resources is crucial for the nation's sustainable development and resilience. This research assesses potential long-term climate change impacts on river runoff in central Italy's highly regulated Aterno-Pescara River watershed. We simulate current and future river runoff using the Soil and Water Assessment Tool (SWAT+). Climate projections from 5 Global Climate Models (GCMs) under two emissions scenarios are used to quantify potential runoff and drought characteristic changes in SWAT+ to investigate future (2015 – 2100) climate change impacts on river runoff. All GCMs predicted increasing daily temperature (up to 0.6 °C decade−1 at 95% confidence level) and decreasing precipitation trends (-16.4 mm decade−1), resulting in negative river runoff trends (-0.036 m3s−1 decade−1). Uncertainties exist regarding variable magnitudes among GCMs and scenarios. Analyzing 12-month standardized precipitation and runoff drought indices using projections data revealed a strong correlation between drought indices (Pearson coefficient ranges between 0.63 - 0.93 among GCMs). The run-sum technique for both indices showed potential frequent, severe, and prolonged future droughts, with meteorological droughts possibly lasting up to 105 months (severity 163) and hydrological droughts exceeding 100 months (severity over 150). This study provides crucial insights for central Italy's policymakers, emphasizing the need for strategies addressing climate change impacts on water resources for future sustainability.