From Noise to Signal: The Future Emergence of Mediterranean Drought

Future aridification and drought intensification pose major risks to the Mediterranean region, yet detecting robust climate change signals remains challenging due to strong internal variability. This work is conducted within the framework of the DROMEDAR (DROughts and ARidification in the MEDiterranean region) project and assesses the emergence of changes in Mediterranean drought characteristics using Single Model Initial-condition Large Ensembles (SMILEs) from two CMIP6 climate models (CanESM5 and MPI-ESM1-2-LR), which allow us to separate the forced signals from internal climate noise. We analyze all available ensemble members, focusing on precipitation- and temperature-driven drought indices, including the Standardized Precipitation Index (SPI), the Standardized Precipitation Evapotranspiration Index (SPEI), and vapor pressure deficit (VPD). Time of Emergence (ToE) diagnostics are applied to identify when statistically robust changes exceed background variability.

 

While observational and reanalysis datasets show no significant historical trends in Mediterranean precipitation, future projections reveal a clear forced drying signal. Under high-emission scenarios, SPI-based drought changes emerge late in the century, whereas SPEI and VPD exhibit a substantially earlier emergence, highlighting the critical role of increasing atmospheric evaporative demand driven by warming. Spatial patterns indicate widespread drying over Mediterranean land areas, with stronger signals in temperature-sensitive indices.

 

These results demonstrate that future Mediterranean aridification cannot be understood from precipitation alone and emphasize the need for multi-model, multi-index, large-ensemble approaches to robustly assess drought risks and support climate adaptation strategies.