H33N-03:
Merging Paleoclimatic Reconstructions, Observations, and Models to Refine Drought Risk Assessments
Wednesday, 17 December 2014: 2:10 PM
Jason E Smerdon, LDEO of Columbia University, Palisades, NY, United States, Benjamin Cook, NASA Goddard Institute for Space Studies, New York, NY, United States, Edward R Cook, Lamont -Doherty Earth Observatory, Palisades, NY, United States and Richard Seager, Lamont Doherty Earth Obs, Palisades, NY, United States
Abstract:
Tree-ring reconstructions of the Palmer Drought Severity Index (PDSI) provide an important estimate of hydroclimate variability over the last several millennia that improve our understanding of regional drought risks and provide a baseline for future drought projections. Merging paleoclimatic information with observational and model data, however, involves important technical considerations associated with data and model uncertainties and the employed drought metric. Here we evaluate the interpretation of different PDSI formulations in various paleoclimatic, observational, and modeling contexts. Potential biases in tree-ring reconstructed PDSI are evaluated using Thorthwaite, Penman-Montieth, and Self-Calibrating Penman-Montieth PDSI as reconstruction targets in three diverse regions of the United States and tree-ring chronologies from the North American Drought Atlas (NADA). Minimal differences are found between the three PDSI reconstructions and all compare favorably to independently reconstructed Thornthwaite-based PDSI from the NADA. Reconstructions also compare well with model-derived estimates of PDSI (Thornthwaite and Penman-Montieth formulations), and near-surface and full-column soil moisture over the 20th century in two collections of model simulations from the Coupled Model Intercomparison Project Phase 5 database. Model-derived Thornthwaite and Penman-Monteith PDSI closely track modeled soil moisture (near-surface and full column) during the 20th century, with differences only emerging in 21st-century projections. These differences confirm the tendency of Thorntwaite-based PDSI to overestimate drying when temperatures exceed the range of its normalization interval; the more physical moisture-balance accounting of Penman-Montieth PDSI compares much better with modeled soil moisture in the projection interval. Remaining regional differences in the secular behavior of projected soil moisture and Penman-Montieth-based PDSI are interpreted in terms of underlying physical processes and temporal sampling. Results demonstrate the continued utility of PDSI as a metric of surface moisture balance and provide a framework for refining assessments of drought risks using a collection of paleoclimatic, observational, and model data.
