Projected changes in the distribution of global Mediterranean climate-type regions

Mediterranean climate-type regions are characterized by warm-to-hot dry summers and mild, wet winters (Csa and Csb categories in Köppen classification). These regions are especially vulnerable to climate change since temperature and precipitation are expected to change in opposite directions. Impacts of extreme events (e.g., severe heat waves and prolonged droughts), challenges in water availability and food security, as well as other aspects of human livelihood, require a detailed global view of future changes in these unique mid-latitude zones.

Here, we explore the observed trends and future distribution of global Mediterranean climate-type regions (MCR). We analyze gridded observations and a bias-adjusted and statistically downscaled dataset of five global Earth System Models from Coupled Model Intercomparison Project phase 6 (CMIP6). For supporting decision-making and climate mitigation efforts, we focus on different global warming levels (e.g., 1.5, 2, 3, and 4°C) derived from the Shared Socioeconomic Pathway SSP5-8.5.

Our preliminary results show that for the rest of the 21st century, the CMIP6 models project that the total MCR area will not change significantly. However, our analysis highlights a robust poleward and eastward expansion of Csa zones at the expense of cooler climates (incl. Csb) over three regions, corresponding to a 21% increase in their area in the Mediterranean Basin, a 41% increase in North America-California, and 12.2% increase in South America-Central Chile. For every one additional degree of global warming, mean rainfall will likely decrease by about 4-5 % in most of the Mediterranean Basin, Southern Africa, and Southern Australia, while in South America-Central Chile, this decrease is more pronounced (near 10%). On the contrary, for every degree of global warming, mean rainfall will likely increase by about 5% in North America-California.