Observation-based Blended Projections from Ensembles of Regional Climate Models

We consider the problem of projecting future climate from ensembles of regional climate model (RCM) simulations using results from the North American Regional Climate Change Assessment Program (NARCCAP). To this end, we develop a hierarchical Bayesian space-time model that quantifies the discrepancies between different members of an ensemble of RCMs corresponding to present day conditions, and observational records. Discrepancies are then propagated into the future to obtain high resolution blended projections of 21st century climate. In addition to blended projections, the proposed method provides location-dependent comparisons between the different simulations by estimating the different modes of spatial variability, and using the climate model-specific coefficients of the spatial factors for comparisons. The approach has the flexibility to provide projections at any spatial scale of potential interest to stakeholders while correctly accounting for the uncertainties associated with projections at that scale. We demonstrate the methodology with simulations from WRF using three different forcings: NCEP, CCSM and CGCM3. We use simulations for two time periods: current climate conditions, covering 1971 to 2000, and future climate conditions under the SRES A2 emissions scenario, covering 2041 to 2070. We investigate and project yearly mean summer and winter temperatures for a domain in the South West of the United States. ∗Esther Salazar is Assistant Research Professor, Department of Electrical and Computer Engineering, Duke University ([email protected]); Dorit Hammerling is Postdoctoral Associate at the National Center for Atmospheric Research ([email protected]) and Department of Statistics, University of Washington; Xia Wang is Assistant Professor, Department of Mathematical Sciences, University of Cincinnati, ([email protected] ); Bruno Sansó is Professor and Chair, Department of Applied Mathematics and Statistics, University of California Santa Cruz ([email protected]); Andrew O. Finley is Associate Professor, Departments of Forestry and Geography, Michigan State University ([email protected]); Linda Mearns is Senior Scientist at the National Center for Atmospheric Research, ([email protected])