Tracing the Waters through the Trees: North American Monsoon Dynamics over the past Four Centuries

北美季风（NAM）调节中美洲、墨西哥和美国西南部的夏季降水，北至拉斯维加斯和大盆地。根据仪器记录，不正运动降雨的开始和总量都随时间振荡，近年来有增加变率的趋势。鉴于海洋、大气和陆地之间的相互作用是不干旱区的特征，本研究项目旨在将现代仪器观测（仅限于几十年）置于较长时间视角，以便充分反映不干旱区变率的范围，并提高我们对年至年代际尺度的潜在过程和驱动力的理解。研究人员将利用对来自北美季风两个地理端点的树木年轮记录的稳定同位素分析获得过去四个世纪以来北美季风变化的信息，这两个端点分别是位于北纬19度左右的墨西哥内华达·德科利马和位于北纬39度左右的美国大盆地国家公园。此外，研究人员将分别使用自动树木计和气象站对树干生长和气候进行密集监测。这些传感器已经在内华达德科利马到位，所需的设备将安装在大盆地国家公园。这项研究将提供关于生长季节长度和径向生长与气候之间日至周关系的详细信息，这些信息对于正确校准北美季风区稳定同位素比率与气候变率之间的关系至关重要。北美热带地区是一个人口稠密的地区，极易受到自然灾害的影响。美国和墨西哥之间的水条约涉及不结盟运动地区，传统上存在争议，并且可能在未来几年受到人口快速增长和气候变化的挑战。目前尚不清楚是东部热带太平洋、西部热带大西洋，还是两者的结合为夏季季风提供了水分。水分的来源也可能从一年到下一年或在更长的时间尺度上变化。项目结果将为北美季风试验（NAME）提供长期视角，该试验是CLIVAR-GEWEX联合过程研究，旨在确定北美暖季降水的来源和可预测性的限制。此外，这两个研究地点都位于山区环境中，尽管这些地区容易受到自然和人为干扰，但监测站很少。拟议的项目将与西部山区综合气候研究联盟（CIRMOUNT）协调，该联盟是最近成立的一个跨学科专家小组，旨在促进山区的气候相关科学。这个项目将加强国家（联合国研究计划署大盆地国家公园地理系）和国际（墨西哥科利马大学、德国于利希地圈沉积系统化学和动力学研究所）研究和教育机构之间的合作。研究结果将通过以下方式广泛传播：专业会议上的报告、研讨会和课堂讲座中的多媒体演讲、同行评议的科学期刊上的文章、PI网站上发布的材料，以及针对中学教师和拉丁裔学生的推广项目中的一对一对话。

The North American Monsoon (NAM) regulates summer precipitation over Central America, Mexico, and the American Southwest, reaching as far north as Las Vegas and the Great Basin. Based on instrumental records, both the onset and total amount of NAM rainfall have oscillated over time, with a tendency towards increased variability in recent years. Given the interplay between ocean, atmosphere, and land that characterizes the NAM region, this research project aims at placing modern instrumental observations (which are limited to a few decades) within a longer temporal perspective in order to fully represent the range of NAM variability and improve our understanding of underlying processes and driving forces at annual to decadal scales. The researchers will obtain information on North American Monsoon variability over the past four centuries using stable isotope analysis of tree-ring records from two geographic endpoints of the NAM, namely Nevado de Colima, Mexico, at about 19 degrees N, and Great Basin National Park, USA, at about 39 degrees N. In addition, the investigators will perform an intensive monitoring of stem growth and climate using, respectively, automated dendrometers and weather stations. These sensors are already in place at Nevado de Colima, and the required equipment will be installed at Great Basin National Park. This research will provide detailed information on growing season length and daily to weekly relationships between radial growth and climate, information that is critical for correctly calibrating stable isotopic ratios against climate variability in the North American Monsoon region.The North American tropics are a heavily populated area that is highly vulnerable to natural disasters. Water treaties between the US and Mexico concern the NAM region, are traditionally contentious, and are likely to be challenged in the coming years by rapid population growth and climatic changes. It is unclear if the eastern tropical Pacific, the western tropical Atlantic, or a combination of both supplies moisture for the summer monsoon. Sources of moisture may also change from one year to the next or on longer time scales. Project results will provide a long-term perspective to the North American Monsoon Experiment (NAME), a joint CLIVAR-GEWEX process study aimed at determining the sources and limits of predictability of warm season precipitation over North America. In addition, both study sites are located in mountain environments, where monitoring stations are scarce despite the vulnerability of these regions to natural and human disturbance. The proposed project will be coordinated with the Consortium for Integrated Climate Research in Western Mountains (CIRMOUNT), an interdisciplinary group of experts recently formed to promote climate-related science in mountainous regions. This project will strengthen collaboration between national (the Department of Geography at UNR, Great Basin National Park) and international (the Universidad de Colima in Mexico, the Institute of Chemistry and Dynamics of the Geosphere Sedimentary Systems in Julich, Germany) research and education institutions. Results will be broadly disseminated using a mix of presentations at professional meetings, multi-media talks during seminars and class lectures, articles in peer-reviewed scientific journals, materials posted on the PI's web site, and as one-on-one conversations during outreach programs aimed at secondary teachers and Latino/a students.