P2C2: Diagnosing the Dynamics of Past and Future North American Megadroughts

该项目旨在探讨被广泛称为特大干旱的数十年干旱的原因和发生情况。 特大干旱有可能通过破坏农业生产、粮食安全、城市供水和生态系统服务对社会产生严重影响。有两方面的证据表明，它们在未来可能会发生：（1）在过去的2,000年里，它们发生在北美，在中世纪早期，几次特大干旱甚至集中在一起;（2）气候模型模拟表明，全球气温的上升将逐步增加本世纪发生特大干旱的可能性。 尽管人们认识到特大干旱的反复发生，但对这些干旱的原因了解不够，因为缺乏与过去特大干旱的重建相一致的气候动态的长期信息。 该项目旨在通过建立一种新型的基于数据同化的全球水文气候重建（其中还包括动态变量的重建）来解决这一明显的缺点。 具体而言，过去的特大干旱的动态特征将被用来测试突出的假设，在美国西南部，中部平原，中美洲的特大干旱的原因，从而帮助诊断其原因在物理上一致的和独立的框架。 理论将进行测试，假设参与太平洋和大西洋海面温度，在热带辐合带和中纬度风暴路径的变化，和外源强迫。 潜在的动力学原因和迫使megadbrought集群在中世纪早期期间也将进行评估。大干旱的动力学特征随后将被用于基准气候和估计世纪大干旱的潜在风险。潜在的更广泛的影响包括更好地了解大干旱及其潜在的社会影响，早期职业科学家的支持，该奖项反映了NSF的法定使命，并被认为是值得通过使用评估的支持。基金会的学术价值和更广泛的影响审查标准。

This project aims to explore the cause and occurrence of multi-decadal droughts, broadly characterized as megadroughts. Megadroughts have the potential to critically affect society through disruptions involving agricultural production, food security, municipal water supplies, and ecosystem services. The possibility that they may occur in the future is suggested by two lines of evidence: (1) they have occurred in North America during the past 2,000 years and several megadroughts even clustered together in time during the early Middle Ages; and (2) climate model simulations suggest that increasing global temperatures will progressively increase the likelihood of a megadrought in this century. Despite the awareness of megadrought recurrence, the causes of these droughts are inadequately understood because of a lack of long-term information about climate dynamics that is physically consistent with reconstructions of past megadroughts. This project seeks to address this apparent shortcoming by producing a novel data-assimilation-based reconstruction of global hydroclimate that also includes a reconstruction of dynamical variables. Specifically, dynamical characterizations of past megadroughts will be used to test prominent hypotheses about the causes of megadroughts in the American Southwest, the Central Plains, and Mesoamerica thereby helping diagnose their causes in a physically consistent and self-contained framework. Theories will be tested that hypothesize involvement by Pacific and Atlantic sea surface temperatures, shifts in the Intertropical Convergence Zone and midlatitude storm tracks, and exogenous forcing. The potential dynamic causes and forcing of megadrought clustering during the early Medieval period will also be evaluated. The megadrought dynamical characterizations will subsequently be used to benchmark climate and to estimate the potential risk of megadroughts in the 21st century.The potential Broader Impacts include greater understanding of megadroughts and their potential societal impact, support of an early career scientist, and involvement of undergraduates in the research.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.