Assessment of Future Precipitation Changes in Mediterranean Climate Regions From CMIP6 Ensemble

Abstract

Previous studies have indicated a large model disagreement in the future projections of precipitation changes over Mediterranean climate (MedClim) regions worldwide. The majority of these highly populated regions have experienced major droughts in the recent decades, raising concerns about future precipitation changes and their impacts. Here, we examine precipitation projections in five MedClim regions from the CMIP6 ensemble, focusing on model consensus regarding the direction and magnitude of future precipitation changes. Our analysis spans the period 2050–2079 relative to 1970–1999, considering two climate change scenarios (SSP2-4.5 and SSP5-8.5) across the Mediterranean Basin (MED), California (CAL), the central coast of Chile (SAA), the Cape Province area of South Africa (SAF), and southwest Australia (AUS). The CMIP6 ensemble mean suggests that annual mean cumulative precipitation will decrease over all the regions except northern California, primarily due to a reduction in winter precipitation, and except over the Mediterranean Basin, where the most significant decrease occurs in autumn. Model agreement on the sign of future precipitation changes is high where the ensemble mean indicates a decrease, but lower where an increase or no changes are projected. Additionally, consecutive dry days (CDD) are expected to increase across all regions, whilst consecutive wet days (CWD) are expected to decrease. Maximum 1-day precipitation is projected to increase uniformly across all regions. We conclude that despite substantial improvements to the new CMIP6 generation of models, the model spread in future precipitation projections in MedClim regions continues to be high. Impact studies need to account for these uncertainties and consider the whole intermodel range of projected precipitation changes.