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

地中海的气候特点是夏季温暖干燥，冬季温和潮湿，为其世界闻名的葡萄园和橄榄园提供了完美的条件。但地中海气候并不是地中海沿岸国家所独有的，类似的情况也存在于美国西海岸、智利中部、非洲南部和澳大利亚西南部，它们都位于各自大陆的西海岸。这些地中海气候区（mcr）位于亚热带的边缘，这意味着纬度低到足以在夏季受到干燥的亚热带反气旋的影响，但又高到足以接受中纬度冬季天气系统的降雨。中纬度地区冬季和亚热带夏季的气候变化对中纬度地区的边缘位置造成了不利影响：如果冬季风暴路径转移到高纬度地区（这是温室变暖的预期后果），中纬度地区可能会出现冬季降雨减少的情况，而由于亚热带干旱地区的扩大，夏季可能会出现热浪和野火。考虑到加州的野火和热浪，以及大西洋风暴路径北上导致西班牙降雨量长期减少，mcr地区的气候变化问题变得更加紧迫。该项目研究了mcr的气候变化，在它们共同的气候特征框架内研究这个问题，并试图将地面上的气候变化与大气大尺度环流中由变暖引起的变化联系起来。一个问题是，尽管这些地区存在共性，但它们的行为差异在多大程度上存在差异，例如，加州没有经历过与伊比利亚半岛相比的冬季降雨量下降。该提案的具体目标是：1)确定与每个MCR相关的风暴路径、急流、副热带高压、下沉以及降水和温度的季节性循环的变化；2)将这些变化与全球大气环流的变化联系起来；3)确定与水资源、野火和农业相关的气候条件的诱发变化。一种紧急约束方法学，在这种方法学中，模式模拟中当前气候的各个方面可以根据观测结果进行检验，这些方面与来自同一模式的未来气候预估的行为有关。该方法提供了一种利用当前观测来评估未来气候预测可信度的方法。考虑到这些地区的人类和自然环境所面临的危害，mcr在气候变暖中的命运既是一个社会问题，也是一个科学问题。首席调查员与MedCLIVAR合作，MedCLIVAR是国际CLIVAR的一个分支组织，负责协调地中海气候研究。当地的外展活动是通过两年一次的拉蒙特开放日进行的。该奖项为研究生提供支持和培训，从而培养该研究领域的未来科学人才。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.