Climatology of the Intermountain West an Assessment of Temperature, Precipitation, and Snowpack in a Changing Climate Regime

Alan Rhoades

Abstract: The western United States, or Intermountain West, is both a variable and intermittent hydroclimate system. Both the natural and human components of the system are dependent on variable temperature, precipitation, and snowpack patterns at different temporal and spatial scales. These dependencies leave the region more susceptible to climate change and the associated impacts. In order to effectively adapt to the changing climate regime, key environmental variables such as temperature, precipitation, and snowpack must be understood via monitoring and modeling. Additionally, effort needs to be focused on developing a better understanding of the large scale teleconnections of the region that drive the variability within the environmental variables. Being able to predict when these teleconnections will arise and how they shift storm tracks within the region will help to constrain management and policy intervention uncertainties for the region. Historically observed trends for the region indicate that temperatures have increased by one to 2.5 degrees Fahrenheit, precipitation trends have been highly variable with a slightly increased trend of 0.5 to 2.1%, and snowpack has declined by 16-22%, over the past 50 years. Global climate models predict similar trends (in several emission scenarios) where temperature increases by two to 5.5 degrees Fahrenheight, precipitation varies between -20% to +15%, and snowpack declines by 21 to 25% by 2055 relative to a 1950-2000 baseline. Water managers should expect to deal with a multivariate and uncertain future that will break down the long standing management strategy of stationarity.