Hydroclimatic variability and trend analysis of the Arno River basin, Tuscany, Italy

Climate change is altering hydroclimatic regimes across the Mediterranean, yet recent basin-scale observational syntheses remain limited for key river basins. This study evaluates hydroclimatic variability and trends in the Arno River basin, Tuscany, Italy, using daily temperature, precipitation, and streamflow records for 1994–2023. Trends were assessed using autocorrelation-corrected modified Mann–Kendall tests, Sen’s slope estimates with 95% confidence intervals, Benjamini–Hochberg multiple-testing correction, and change-point diagnostics. Statistically significant warming was detected in summer (+ 0.066 °C yr −1 ) and autumn (+ 0.073 °C yr −1 ), both trends remaining significant after multiple-testing correction. Annual mean temperature increased by + 0.052 °C yr −1 , equivalent to + 1.56 °C over 30 years, but did not remain significant after multiple-testing correction. A significant temperature change-point occurred around 2010, while no change-points were detected for precipitation or streamflow. No significant monotonic trends were detected for precipitation or streamflow at annual or seasonal scales, although the 30-year record and high interannual variability (CV up to ~ 36% for precipitation and ~ 66% for streamflow) limit exclusion of small trends. Precipitation displayed a clear orographic gradient, with higher values along the Apennine ridge and lower values in lowlands. Precipitation and streamflow were positively correlated across all seasons (ρ = 0.51–0.93), indicating strong precipitation-runoff coupling. Summer temperature was negatively correlated with streamflow (ρ = − 0.53, p = 0.003; pBH = 0.009), consistent with warm-season hydroclimatic sensitivity, although this observational association does not establish causation. These findings provide an updated observational baseline for hydroclimatic monitoring and climate-adaptation planning in the Arno River basin.