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

该项目旨在探索多年代际干旱的原因和发生，通常被称为特大干旱。特大干旱有可能通过破坏农业生产、粮食安全、市政供水和生态系统服务来严重影响社会。有两方面的证据表明，它们可能在未来发生：(1)在过去的2000年里，它们在北美发生过，在中世纪早期，几个特大干旱甚至同时发生；(2)气候模式模拟表明，全球气温上升将逐步增加本世纪发生特大干旱的可能性。尽管人们意识到特大干旱的复发，但由于缺乏与过去特大干旱的重建在物理上一致的气候动力学的长期信息，对这些干旱的原因还没有充分了解。该项目旨在通过产生一种新的基于数据同化的全球水文气候重建来解决这一明显的缺点，该重建还包括动态变量的重建。具体来说，过去特大干旱的动力学特征将被用来检验关于美国西南部、中原和中美洲特大干旱原因的重要假设，从而帮助在一个物理一致和独立的框架中诊断其原因。将对太平洋和大西洋海面温度、热带辐合带和中纬度风暴路径的变化以及外源强迫的假设参与的理论进行检验。还将评估中世纪早期特大干旱聚集的潜在动力原因和强迫。随后，这些特大干旱的动力学特征将被用于气候基准和估计21世纪特大干旱的潜在风险。潜在的更广泛的影响包括对超级计算机及其潜在社会影响的更好理解，对早期职业科学家的支持，以及本科生参与研究。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。

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.