Abstract
<jats:p>The Mediterranean Basin is typically classified as a region with decreasing streamflow and as a hotspot for future climate change, with important impacts on agricultural and ecosystem functioning. Here we present an assessment of past trends and future projections of water resources at the scale of the Mediterranean Basin. We evaluated how historical climate change, vegetation greening, and reservoir construction affected Mediterranean discharge trends, based on over a century of discharge trends (1914–2022) obtained from 654 discharge stations across the Mediterranean Basin. The results show that mean discharge trends align mostly with precipitation trends between 1921-2000, distinguishing periods of significant increasing (1941–1971) and decreasing discharge (1961–2000). However, between 1981 and 2020 the relationship between precipitation and mean discharge mostly diminishes. We show through multiple linear regression that precipitation and vegetation greenness have an equally strong but counteracting effect on runoff. Reservoir construction caused a reduction of the mean and maximum discharge. Furthermore, we assessed the impact of climate change on water resources, which is predominantly studied through the application of hydrological models forced by climate model output. Through a systematic review we analysed the results of 262 Mediterranean climate change assessments. We show that runoff is projected to decrease on average with 19%, with a stronger decrease towards the end of the century and with increasing emission scenarios (up to −39%). Similarly, soil moisture (−14%) and aquifer recharge (−21%) are also negatively affected by climate change, while irrigation demand is projected to increase (8%). While past trends were shown to be heavily affected by vegetation development and reservoir construction, most future hydrological assessments focus solely on the impact of climate change, neglecting vegetation development. This urges future studies to incorporate vegetation development and anthropogenic activities into these assessments, to obtain more accurate water resources projections, including possible feedbacks.</jats:p>