PP033-02
Placing the east-west United States aridity gradient in a millennial context

Friday, 11 December 2020: 19:04
Virtual
Daniel A Bishop, Columbia University of New York, Earth and Environmental Sciences, New York, NY, United States, Park Williams, Columbia University, Lamont -Doherty Earth Observatory, Palisades, NY, United States, Richard Seager, Lamont Doherty Earth Obs, Palisades, NY, United States, Kasey Bolles, Baylor University, Department of Geosciences, Waco, TX, United States, Edward R Cook, Columbia University of New York, Lamont-Doherty Earth Observatory, Palisades, NY, United States, Dorothy M Peteet, NASA Goddard Institute for Space Studies, New York, NY, United States, Benjamin I Cook, National Aeronautics and Space Administration Goddard Institute for Space Studies, New York, United States and Mukund Palat Rao, Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, United States
Recorded Presentation
Abstract:
Global climate change is projected to exacerbate regional droughts across much of the globe by the end of the 21stcentury, while increases in precipitation extremes are projected to increase regional flood risk. In the United States (US), instrumental records indicate a trend over the past century towards drier soil moisture conditions over a large portion of the western US and wetter conditions over the eastern US, termed here as the east-west US aridity gradient. A continuation of these trends into the future would have significant hydroclimatic and socioeconomic consequences in both the semi-arid southwestern and humid eastern US. Contextualizing this trend over the last 500 years would improve our understanding of its underlying drivers and help benchmark future climate change projections. Using tree-ring reconstructions and hydrologic models of summer soil moisture, we seek to (1) evaluate and contextualize the spatial characteristics and physical mechanisms of the modern summer (JJA) aridity gradient trend within its natural range of climate variability, and (2) decompose the effects of continental, regional, and seasonal observed precipitation and vapor pressure deficit (VPD) trends in driving the observed intensification of the aridity gradient. Combining observations with our reconstruction, the mean soil-moisture difference between the east and west US during 1999–2018 was larger than during any other 20-year period since the turn of the 17th century. The observed summer aridity gradient trend was primarily driven by summer and fall precipitation increases in the Midwest and Northeast US, and annual VPD increases and winter precipitation decreases in the Southwest US. Additional work will assess simulations of historical and future climate to investigate the potential contribution of anthropogenic VPD and precipitation trends to the strengthened aridity gradient observed over the past century. This will provide insight into how this gradient may change in future decades, with significant implications for regional human and ecological health, socioeconomics, water resources, and agriculture.

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