One-half-degree gridded daily-projection precipitation model output of two combinations of the Canadian Regional Climate Model (CRCM)—one driven by the Community Climate System Model (CCSM) and another by the Canadian Global Climate Model phase3 (CGCM3)—was obtained from the North American Regional Climate Change Assessment Program (NARCCAP). Gridded observational daily precipitation data were used as a reference to a 1971-1995 historic period and as a basis for validating the projection data. Validation suggested strong bias in the projection data, which led to bias correction by a mean-value technique. Both the observational and projection data were ranked and assigned percentile values as a means of identifying and quantifying possible changes in extreme precipitation between the historic 1971-1995 and a future 2041-2065 period over two 1/2-degree grid squares that were centered over Houston and Oklahoma City. However, follow-up analysis also indicated that a more sophisticated bias-correction procedure based on rain rate is necessary due to a lack of homogeneity in bias for different magnitudes of daily precipitation value.

Overall, results of a percentile analysis that compared historic output data of a particular model combination to future output data of the same model combination provided evidence that, for the highest percentile ranking (i.e., 100, or that associated with the maximum daily precipitation value), the daily precipitation values associated with this ranking will increase by the 2041-2065 period. This result was noted more in the Houston analysis than in the Oklahoma City analysis, suggesting spatial variability in this tendency. For more moderate percentile rankings (i.e., 90, 95, 97.5, 99, and 99.5), the tendency toward change was less clear. For lower percentile rankings (i.e., 80), there was indication that the values associated with a given percentile ranking will decrease by the future period.