Impact of Climate Change on Heavy Precipitation Events : Application of Extreme Value Theory to a Future Climate Simulation over the Colorado Headwaters Region

Heavy precipitation cause devastating warm-season floods and cool-season snow and icing hazards that impact socio-economic communities of various scales. The frequency and severity of extreme precipitation events potentially are likely to be impacted by climate change. In this study we will investigate potential change in extreme precipitation intensity in a future climate over the Colorado headwaters region based on an extreme value approach ("peak-over-threshold" approach). The data come from Weather Research and Forecasting (WRF) model simulations of current and future climate conducted by the Colorado Headwaters Project (e.g., Rasmussen et al. 2011). The simulations were performed over eight years with 4, 12, and 36 km horizontal grid spacing. In the current study, we first evaluate the model ability to properly represent extreme precipitation events from the current climate simulation. Then we present changes in extreme precipitation intensity in the future climate for different seasons and over eight mountain ranges of the Colorado headwaters region. Our analyses so far have shown that the 4-km model outperformed coarser grid resolution models in representing extreme precipitation compared to Snowpack Telemetry (SNOTEL) surface observations. Overall, the 10-year return level in the future climate increased (more intense extreme precipitation) for all mountain ranges in the cool season. There was a general decrease in the 10-year return level (less intense extreme precipitation) in the warm season. The sign and magnitude of the change shows regional differences possibly related to seasonal storm tracks and characteristics. Detailed analysis from case studies will be presented to illustrate the impacts of a warmer and moister atmosphere on the microphysical structure of storm clouds and surface precipitation distribution.