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

这一合作项目的总体目标是对树木年轮代用指标和气候模拟进行数据模型综合，以确定十年至百年气候变率的强度和起源，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，有必要了解十年到百年（dec-cen）时间尺度上气候变化的起源、模式和幅度。如果dec-cen变化很弱，该团队假设气候变化对区域水文气候的影响可能会由于辐射强迫的缓慢变化而显现。然而，如果dec-cen变化很强，那么研究小组认为，在任何对气候的理解中，都应该共同考虑大气变暖和自然变化在长时间尺度上的综合影响。研究小组特别寻求量化模型，代理和观测中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上千年数值气候模型。他们将把统计和动态降尺度技术应用于这个集合，包括一个超高（时间）分辨率控制模拟运行，并使用这些结果来推动树木年轮生长的模型。此外，研究人员将重新处理国际树轮数据库存档的北方半球所有树轮宽度和密度测量值，以优化deccen变异的幅度和空间结构。 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优化的树轮网络--将使用一个强有力的零假设对dec-cen变率的幅度和空间结构进行评估。这些活动将，反过来，提高全幅度dec-cen变异的理解，其空间足迹，其相关性，以未来megadbrought risk.The更广泛的影响涉及组织两个研讨会的古气候研究人员和统计学家，探索新的方法推断，从这个数据集。此外，在北美树木年轮网络的dec-cen模式的全面分析将直接解决正在进行的辩论的起源时间自相关的树木年轮记录和潜在的混淆影响的生物持久性对气候历史估计从这个代理。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.