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

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.