A Comparison Between North American Regional Climate Change Assessment Program Output and Oklahoma Mesonet Observations: Precipitation

On May 10, 2011, the Southern Climate Impacts Planning Program and the Oklahoma Climatological Survey co-hosted a meeting of climate-aware stakeholders, including federal, state, tribal, and municipal decision makers in Oklahoma. Many of these stakeholders expressed concerns that long-term climate predictions are not local enough and do not effectively communicate the importance of observed and predicted trends to their specific needs. Although fully addressing those concerns requires a much broader scope, this study was motivated by these stakeholder concerns.

The focus of this research is to regional climate model output from the North American Regional Climate Change Assessment Program (NARCCAP) with observations from the Oklahoma Mesonet for the variables of precipitation and temperature. The Oklahoma Mesonet provides high-quality, county-level climate data from 1994 to the present. The purpose of the study is to better understand how well the combinations of global and regional climate models in NARCCAP represent the strong east-to-west gradient and seasonality of precipitation across Oklahoma. Annual, seasonal, and monthly statistics were calculated and compared among the datasets of two regional climate models (RCMs), the Mesoscale Model 5 (MM5) and the Weather Research and Forecasting Model (WRF), that have been driven by the Community Climate System Model (CCSM) and the NARCCAP National Center for Environmental Prediction (NCEP) Reanalysis.

Although many other studies have compared NARCCAP output to surface observations, this research is the first that compares the regional climate model output with observations from such a rich source of quality surface observations. Using 5 to 6 years of overlapping data from the observations and the models, the results indicate that the models consistently overestimate cold season precipitation, and underestimate, to a much greater magnitude, warm season precipitation, with the magnitude of percent error much higher for those runs driven by the CCSM global climate model. Likewise, there is little evidence to suggest that these models are accurately portraying convective precipitation, which accounts for much of Oklahoma's rainfall, especially in warm seasons. The authors will present these preliminary results from this research, including a statistical comparison of temperature and precipitation variables output from the regional climate models and observations from the Oklahoma Mesonet.