Collaborative Research: P2C2--Quantifying the Risk of Widespread Megadrought in North America

这一合作项目通常旨在进行树轮代理和气候模拟的数据模型合成，以确定十年百年气候变异性的强度和来源。该研究的科学目标是预测持续十年或更长时间的干旱风险。因此，研究小组认为，有必要了解气候变化在十年到百年(十年至十年)的时间尺度上的起源、模式和幅度。如果12月变化很弱，研究小组假设，气候变化对区域水文气候的影响很可能是辐射强迫缓慢变化的结果。然而，如果12月变化很大，那么研究小组认为，在任何对气候的理解中，都应该联合考虑大气变暖和自然变化对长时间尺度的综合影响。研究小组特别寻求在模型、代理和观测中量化低频水文气候变化的幅度，同时利用国家大气研究中心制作的一套新的过去千年的数值气候模式。他们将把统计和动态缩小尺度技术应用到这个集合中，包括一次超高分辨率(时间)控制模拟运行，并使用这些结果来推动树木年轮生长的向前模型。此外，研究人员将重新处理国际树轮数据库存档的北半球所有树轮宽度和密度测量数据，以优化年轮变率的幅度和空间结构。这两个产品来自气候模型的高分辨率树轮模拟和新的dec-cen优化树环网络将使用关于dec-cen变率的幅度和空间结构的稳健的零假设进行评估。这些活动反过来将增进对整个十年十年变率、其空间足迹及其与未来特大灾害风险的相关性的理解。更广泛的影响包括为古气候研究人员和统计学家组织两次研讨会，以探索根据这一数据集进行推断的新方法。此外，对整个北美树轮网络的12月-cen模式的综合分析将直接涉及正在进行的关于树轮记录中时间自相关的起源的辩论，以及根据这一指标估计的生物持续性对气候历史的潜在混杂影响。此外，该项目将在研究过程中支持两名研究生。

This collaborative project generally aims to undertake a data-model synthesis of tree-ring proxies and climate simulations to identify the strength and origins of decadal-centennial climate variability.The science goal of the research is to anticipate the risk of droughts lasting one or more decades. As such, the research team argues that it is necessary to understand the origins, patterns, and amplitudes of climate variability at decadal to centennial (dec-cen) timescales. If dec-cen variations are weak, the team hypothesizes that climate change impacts on regional hydroclimate will likely unfold as a consequence of slow-varying changes in radiative forcing. If dec-cen variations are strong, however, then the team argues that the combined effects of atmospheric warming and natural variability on long timescales should be considered jointly in any understanding of climate.The research team specifically seeks to quantify the amplitude of low-frequency hydroclimatic variability in models, proxies, and observations, while at the same time utilizing a new suite of last millennium numerical climate models produced by the National Center for Atmospheric Research. They will apply both statistical and dynamical downscaling techniques to this ensemble, including one ultra-high (temporal) resolution control simulation run and use these results to drive forward models of tree-ring growth. Further, the researchers will reprocess all tree-ring width and density measurements from the Northern Hemisphere archived by the International Tree-Ring Databank to optimize the amplitude and spatial structure of dec-cen variability. Both of these products - the high-resolution tree-ring simulations from climate models and the new dec-cen optimized tree-ring network - will be evaluated using a robust null-hypothesis for the amplitude and spatial structure of dec-cen variability. These activities will, in turn, improve the understanding of the full magnitude dec-cen variability, its spatial footprint, and its relevance to future megadrought risk.The Broader Impacts involve organizing two workshops for paleoclimate researchers and statisticians to explore new methods of inference from this dataset. In addition, the comprehensive analysis of dec-cen patterns across the North American tree-ring network will address directly the ongoing debate about the origins of temporal autocorrelation in tree-ring records and the potential confounding effects of biological persistence on climate histories estimated from this proxy. Furthermore, this project will support two graduate students in the course of the research.