Vegetation greening and reservoir construction as drivers of century-long discharge trends in the Mediterranean Basin

Abstract

The Mediterranean Basin is typically classified as a region with decreasing streamflow trends since the 1960s, despite high variability in precipitation. Here we evaluated over a century of discharge trends (1914–2022) with data obtained from 654 discharge stations across the Mediterranean Basin from national and continental discharge databases. We assessed several drivers of discharge trends, including climate change, vegetation greening and reservoir construction. Trends in mean discharge align mostly with precipitation trends, showing distinct periods of statistically significant increasing (1941–1971) and decreasing discharge (1961–2000). Yet, mean discharge has been remarkably stable between 1981–2020, diverging from the significantly increasing precipitation trends for this period. Multiple linear regression confirmed that recent precipitation and vegetation greenness trends have an equally strong but counteracting effect on runoff trends. Reservoir construction caused a further consistent decrease in mean and maximum discharge, and weakened the natural discharge regime. Our study concludes that over the last century, discharge trends in the Mediterranean Basin can only partly be explained by precipitation variability. Reservoir construction and recent vegetation greening are identified as additional strong drivers of discharge trends. • Century-long Mediterranean discharge trends analysed using data from 654 stations. • Focus on climate, greening-up and reservoir construction as drivers of change. • Trends in mean discharge align mostly with precipitation trends from 1921–2000. • Precipitation and vegetation greenness counteract their effect on runoff (1982-2022). • Reservoir construction weakened the natural discharge regime.