Future Projections of Heavy Rainfall Values in NOAA Atlas 15

NOAA Atlas 15 (NA15) is currently under development. Volume 2 of NA15 will provide heavy precipitation frequency design values that incorporate potential future climate change. There is a strong monotonic statistical relationship in historical observational data between extreme precipitation amounts and atmospheric water vapor content. This suggests increased frequency of high intensity precipitation in a warmer world because of the increase in saturation water vapor pressure with increasing air temperature following the Clausius-Clapeyron relationship. However, the quantitative effects are much more complex. The Intergovernmental Panel on Climate Change's Sixth Assessment Report states that it is very likely to virtually certain that the intensity and frequency of heavy precipitation will increase if global warming exceeds 2 degrees C, due to the increase in saturation water vapor pressure with increasing temperature following the Clausius-Clapeyron relationship. A suite of datasets based on climate models is being used to quantify these relationships. These datasets include three statistically-downscaled datasets based on CMIP6: the Localized Constructed Analogues version 2 (LOCA2), the Seasonal Trends and Analysis of Residuals (STAR), and the University of Wisconsin Probabilistic Downscaling (UWPD). They also include dynamically downscaled datasets, such as the United States Geological Survey’s (USGS) CONUS404, the NA-CORDEX suite, and a Northern Illinois University simulation. This presentation will describe the methods being used to construct estimates of future heavy precipitation frequency values and the results for a NA15 pilot project in Montana.