Regional climate model experiments to determine the sensitivity of climate variability to slow climate changes in Central America

Efforts to assess the impact of anthropogenic climate change on key societal sectors are limited by the poorly-characterized behaviors of higher-frequency climate variability under the slowly-changing climate baseline. Climate impacts analyses often require information about climate extremes from daily to seasonal time scales at resolutions relevant to stakeholders. These higher temporal resolutions are not available for most global climate models (GCMs) archived from the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4), and many GCMs are at a spatial resolution that is relatively coarse compared to stakeholder needs. This is particularly true in locations with complex topography.

Results are presented from a regional climate modeling (RCM) experiment designed to assess the manner by which higher-frequency climate variability is modified by anthropogenic climate changes on decadal (and longer) scales. The Weather Research and Forecasting (WRF) model is driven over a large Central American domain by the NCAR Community Climate System Model (CCSM)'s 20th Century, A2, and B1 emissions scenarios at 3-hourly and 32-km resolution on the Discover cluster at the National Center for Computer Services (NCCS). To evaluate the capabilities of the modeling system, daily temperature and precipitation distributions are compared during the 1970-2000 baseline from the WRF/CCSM experiment, from a 1980-2000 WRF/Reanalysis-2 experiment, and from more recent high-resolution precipitation products. Daily distributions are evaluated by season, as well as by El Nino / Southern Oscillation phase as a historical proxy for slower climate changes. The WRF/CCSM baseline conditions are then compared to A2 and B1 scenarios covering the 2020-2050 period, revealing the changing character of extreme events. Results reveal an uneven shift in the distributions that tend to smooth out unique climatic regimes.