Amplification of soil moisture seasonality and compound warm–dry conditions over the Mediterranean under future climate scenarios

The Mediterranean region is widely recognized as a climate-change hotspot, where rising temperatures and declining precipitation are expected to intensify hydroclimatic stress. Most Mediterranean countries already experience increasing drought frequency and persistent soil moisture deficits leading to changes in terrestrial water storage. However, projected changes in the seasonal structure of soil moisture and its joint behaviour with temperature and precipitation remain insufficiently quantified.

Here, we assess future projections of soil moisture dynamics and compound warm–dry conditions across the Mediterranean using a multi-model ensemble of EURO-CORDEX regional climate simulations. We analyse daily total soil moisture, precipitation, 2-m temperature, and potential evapotranspiration for a historical baseline period (1971–2000), and three future periods (2011–2040, 2041–2070, 2071–2100) under three emission scenarios (RCP2.6, 4.5 and 8.5). Seasonal amplitude and phase changes in soil moisture are examined, and joint probability density functions are used to quantify compound warm–dry conditions and their drivers.

The projections show a clear reduction of soil moisture throughout the entire annual cycle, in response to a significant decrease in precipitation and an increase in temperature, leading to a substantial rise in potential evapotranspiration. The overall total soil moisture decreases ranges from -5% for the RCP2.6 to -20% (-10%) for the RCP8.5 (RCP4.5), with relation to the present climate. Projections reveal that for the RCP4.5 (RCP8.5) for the mid-century soil moisture deficits up to 5x (6x) are projected to occur, and for the end-of-century even 7x for the RCP8.5. Our results show a robust amplification of soil moisture seasonal amplitude across all Mediterranean sub-regions, increasing with higher greenhouse gas emissions and toward the end of the century. The largest increases are projected over the eastern Mediterranean, reflecting enhanced seasonal contrasts driven by intensified summer drying. Despite these amplitude changes, the phase of the soil moisture annual cycle remains stable across scenarios, indicating that climate change primarily intensifies existing seasonal dynamics rather than shifting their timing. Joint probability analyses show a substantial increase in the likelihood of compound warm–dry conditions, particularly under RCP4.5 and, more pronounced under RCP8.5, during mid- and late-century periods.

Overall, our findings highlight that future Mediterranean hydroclimatic risk is driven not only by mean drying but also by a pronounced intensification of soil moisture variability and compound extremes. These projections have important implications for ecosystem, water resources, and climate adaptation strategies.

 

This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 - https://doi.org/10.54499/LA/P/0068/2020, UID/50019/2025, https://doi.org /10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025. The authors would like also to acknowledge the project “Elaboração do Plano Municipal de Ação Climática de Barcelos (PMACB). This work was performed under the scope of project https://doi.org/10.54499/2022.09185.PTDC (DHEFEUS). DCAL acknowledge FCT I.P./MCTES (Fundação para a Ciência e a Tecnologia) for the FCT https://doi.org/10.54499/2022.03183.CEECIND/CP1715/CT0004.