The CASCADE D&A team is fully committed to using the highest resolution climate models possible on the machines at DOE’s National Energy Research Supercomputing Center. We have demonstrated that high resolution (of the order 25km) is a necessary but not sufficient condition to reproduce the distribution of extreme daily averaged precipitation. Working closely with the CASCADE statistics and software teams, we have applied extreme value statistics to a variety of observed and simulated daily precipitation products to quantify model performance in simulating extreme precipitation.

The figure to the left shows comparisons of the annual probability density distributions of daily precipitation between the range of observed precipitation and three different CAM5.1 horizontal resolutions over the contiguous United States. Only the high-resolution model (blue) falls within the range of observational uncertainty.

The  figure to the right shows twenty-year return values (simulated and observed) of the boreal winter maximum daily precipitation over land. Observations are calculated from the period 1979-1999. Model results are calculated from the period 1979-2005. All results are shown at the native resolution.

Source: Wehner et al. (2014) The effect of horizontal resolution on simulation quality in the Community Atmospheric Model, CAM5.1. Early online release: Journal of Modeling the Earth System 06, doi:10.1002/2013MS000276.