P2C2: Decomposition and Reconstruction of Drought Variability Across the Continental United States and Northern Mexico

DESCRIPTION: The western United States (U.S.) and northern Mexico have experienced intense and prolonged droughts over the past two decades that have reduced water resources, enhanced wildfire activity, and raised concerns regarding whether water policies are designed for a sufficiently wide range of future possibilities. Concurrently, much of the eastern U.S. experienced a centennial wetting trend, minimal warming, and repeated floods, but paleo evidence indicates that this region is nonetheless prone to devastating decade-scale droughts.

It is unclear if these contrasting trends are dynamically related and whether they have been aided by anthropogenic forcing. The observed low-frequency hydroclimate events that motivate this research are abnormal in the observational record, but paleoclimate reconstructions indicate that extreme, prolonged swings in hydroclimate often occur naturally. The aim of the project is to extend a range of spatially continuous drought metrics for at least 1,200 years.

This project will use new gridded reconstructions of annual hydroclimatic variability over the past millennium to better understand the drivers of low frequency, decadal scale hydroclimate variability across the US and northern Mexico using three research approaches: (1) determine the degree to which anthropogenic warming has altered the millennial standing of observed soil-moisture in recent decades; (2) reconstruct the leading modes of interannual to multi-decadal drought variability over the past millennium across the U.S. and northern Mexico, with particular focus on a mode critical for California water resources and a mode reflecting an east-west dipole that may lend insights regarding observed multi-decade trends; and (3) reconstruct and diagnose the east-west dipole in drought variability across the U.S. and determine how the expected magnitude of natural multi-decade variations in this mode map onto projected climate trends.

The broader impacts involve support for an early career scientist and the development of regional- and continental- scale reconstructions of hydroclimate variability in the United States spanning the past millennium of value to water resource managers.

OUTCOMES: Cook, Benjamin I. and Williams, A. Park and Mankin, Justin S. and Seager, Richard and Smerdon, Jason E. and Singh, Deepti. "Revisiting the Leading Drivers of Pacific Coastal Drought Variability in the Contiguous United States," Journal of Climate, v.31, 2018. doi:10.1175/JCLI-D-17-0172.1 Citation details

Park Williams, A. and Cook, Benjamin I. and Smerdon, Jason E. and Bishop, Daniel A. and Seager, Richard and Mankin, Justin S.. "The 2016 Southeastern U.S. Drought: An Extreme Departure From Centennial Wetting and Cooling: The 2016 Southeastern U.S. Drought," Journal of Geophysical Research: Atmospheres, v.122, 2017. doi:10.1002/2017JD027523 Citation details

Mankin, Justin S. and Seager, Richard and Smerdon, Jason E. and Cook, Benjamin I. and Williams, A. Park and Horton, Radley M.. "Blue Water Trade-Offs With Vegetation in a CO 2 -Enriched Climate," Geophysical Research Letters, v.45, 2018. doi:10.1002/2018GL077051 Citation details