Climate Change Impact on River Runoff and Drought Characteristics in the Arno River Basin, Tuscany, Italy

This study assesses climate change impacts on river runoff and drought characteristics in the Arno basin using the SWAT+ hydrological model coupled with climate projections from multiple Global Climate Models (GCMs). Hydrometeorological data from precipitation and temperature stations, and hydrometric measurements on the lower Arno River (1994-2014) are being utilized to calibrate and validate the SWAT+ model, with initial results showing good performance during both calibration and validation periods.

Future climate projections are derived from five CMIP6 GCMs under two Shared Socioeconomic Pathway scenarios (SSP2-4.5 and SSP5-8.5) for three future periods: near (2015-2040), mid (2041-2070), and far (2071-2100). Quantile Delta Mapping is employed for bias correction of GCM outputs. Preliminary multi-model ensemble analysis reveals warming trends across all GCMs and scenarios, with more pronounced temperature increases under the higher emission scenario. Precipitation projections indicate decreasing trends, more significant under the SSP5-8.5 scenario. Consequently, river runoff is projected to decrease over time, with the highest model agreement in the far future period.

Drought analysis is being conducted using Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) at different time scales. Initial correlation analysis between SPI and SRI indicates relationships between meteorological and hydrological droughts across all time segments. Early findings suggest that long-term drought patterns show stronger precipitation-runoff relationships than short-term drought events, particularly in the mid and far future periods.

This research aims to provide insights for water resource managers and policymakers, highlighting the need for adaptive management strategies and sustainable water governance to mitigate the potential impacts of climate change on the Arno River basin. The study underscores the importance of implementing resilient water management practices to ensure water security in the face of projected hydroclimatic changes, and a case study that could be implemented to other river basins.