Science Challenges for Constructing 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. 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. The contents of NA15 include precipitation frequency values for durations of 5 minutes to 60 days and annual exceedance probabilities (AEPs) from 0.5 to 0.001. These large ranges pose significant science challenges. One major challenge involves shorter durations, particularly at the far end of the range, from 5 minutes to hourly. At such durations, individual convective cells are likely to be important. The physics of the effect of global warming on convection dynamics can be explored with convection-permitting climate model simulations, but there are few of those because of the massive computational resources required to produce such simulations. Very low AEPs also represent a challenge, one consideration being whether climate models simulate the very rare conditions that might produce such events. This talk will explore these challenges in more detail.