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

该合作项目的总体目标是进行树木年轮代用物和气候模拟的数据模型综合，以确定十年-百年气候变率的强度和起源。这项研究的科学目标是预测持续十年或十年以上的干旱的风险。因此，研究小组认为，有必要了解十年到百年（十百年）时间尺度上气候变化的起源、模式和幅度。如果decc的变化很弱，研究小组假设气候变化对区域水文气候的影响可能会随着辐射强迫的缓慢变化而展开。然而，如果12月的变化是强烈的，那么研究小组认为，在任何对气候的理解中，应该共同考虑大气变暖和自然变率在长时间尺度上的综合影响。研究小组特别寻求在模式、代用物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千年数值气候模型。他们将应用统计和动态降尺度技术，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模型。此外，研究人员将重新处理由国际树木年轮数据库保存的北半球所有树木年轮宽度和密度测量数据，以优化十二年变率的幅度和空间结构。这两个产品——来自气候模式的高分辨率树木年轮模拟和新的12年优化的树木年轮网络——将使用对12年变化幅度和空间结构的稳健零假设进行评估。反过来，这些活动将提高对decoci变异性、其空间足迹及其与未来特大干旱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，以探索从该数据集推断的新方法。此外，对整个北美树木年轮网络的十年模式的综合分析将直接解决正在进行的关于树木年轮记录中时间自相关的起源的争论，以及从这一代理估计的生物持久性对气候历史的潜在混淆影响。此外，该项目将支持两名研究生在研究过程中。

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.