Regional Climate Model Superensemble Simulations of Recent trends in Extreme events for the western US

One of the most prominent impacts of climate change over the western United States is the potential for an elevated number of extreme events over the region. Recent events such as the 2011 Texas drought and heat wave have been shown to be more likely due to anthropogenic climate change. One of the projected impacts of global climate change is increases in extreme rainfall episodes. Over the Pacific Northwest, recent years have seen an upswing in heavy precipitation events such as the Chehalis River floodplain floods of 2007 and 2009 in western Washington state. This study analyzes climate model output derived from the regional climateprediction.net (CPDN) project, with greenhouse gas concentrations and other climate forcings representative of the 1960s and present day. Through the use of public volunteered distributed computing, the project provides an ensemble size that is large enough to examine the tails of the distribution of climate variables. Specifically, the present study compares the decade of the 2000s and one in which global climate change had not influenced (1960s). Analysis of return periods for maximum daily precipitation shows that, for the October-November-December season, the 2000s consistently surpass the 1960s by 5% for events with return periods higher than 60 years. The average maximum daily temperature in a month is also shown to be warmer and with higher frequency in the 2000s compared to the 1961-1990 period for the western US, but with greater changes over the Pacific Northwest.