Changes in Impacts-relevant Climate in the World's Mediterranean Climate Regions: A Mechanisms-based Investigation of Atmosphere-Ocean-Land Processes Across Seasons

The climate of the Mediterranean features warm dry summers and mild wet winters, perfect conditions for its world-renowned vinyards and olive groves. But the Mediterranean climate is not unique to the countries bordering the Mediterranean Sea, as similar conditions exist on the US west coast, central Chile, southern Africa, and southwest Australia, all situated along the west coasts of their respective continents. These Mediterranean Climate Regions (MCRs) are found at the margins of the subtropics, meaning latitudes low enough to be under the dry subtropical anticyclones in summer but high enough to receive rain from the winter weather systems of the middle latitudes. The marginal location of the MCRs makes them vulnerable to changes in climate associated with both the midlatitude winter and the subtropical summer: if the winter storm paths shift to higher latitudes, an expected consequence of greenhouse warming, the MCRs could see loss of winter rain, while summers could experience heat waves and wildfires due to the expansion of the subtropical dry zones. The issue of climate change in MCRs has taken on some urgency given the wilfdires and heat waves in California and the long-term decline in rainfall over Spain as the Atlantic storm paths have shifted northward.

This project examines climate change in the MCRs, examining the issue in the framework of their shared climatic features and attempting to relate climate change on the ground to warming-induced changes in the large-scale circulation of the atmosphere. One issue is the extent to which the regions behave differently despite their commonalities, for instance California has not experienced a decline in winter rainfall comparable to the Iberian Peninsula. The specific goals of the proposal are to 1) identify the changes in storms tracks, jet streams, subtropical highs, subsidence and seasonal cycles of precipitation and temperature that matter for each MCR, 2) relate these to changes in the global atmospheric circulation and 3) determine the induced changes in climatic conditions relevant to water resources, wildfire, and agriculture. An emergent constraint methodology, in which aspects of present-day climate in model simulations, which can be checked against observations, are related to the behavior of future climate projections from the same models. The methodology provides a way to use present-day observations to assess the credibility of future climate projections.

The fate of MCRs in a warming climate is a question of societal as well as scientific interest given the hazards facing people and the natural environment in these regions. The Principal Investigators work with MedCLIVAR, a subgroup of International CLIVAR that coordinates Mediterranean climate research. Local outreach is conducted through the biennial Lamont Open House. The award provides support and training to a graduate student, thereby developing the future scientific workforce in this research area.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.