Twenty-first century central Rocky Mountain river discharge scenarios under greenhouse forcing

摘要

The present-day hydroclimatology of the central Rocky Mountains is heavily influenced by recurring large-scale climate patterns: the Pacific Decadal Oscillation (PDO), the El Nino-Southern Oscillation (ENSO), and the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). Hence, low frequency central Rocky Mountain river discharge variability can be successfully modeled by regression techniques using these climate indices as predictors. Generalized Least Squares (GLS) regression equations captured a large portion of streamflow variability at the hydrological apex of North America. Using archived runs from global climate models from the IPCC Fourth Assessment Report (AR4) (Phase 3 of the Coupled Model Intercomparison Project-CMIP3), the PDO, ENSO and the NAO were projected for the 21st century for the B1, A1B and A2 Special Report on Emission Scenarios (SRES). These projected climate indices were used as inputs into the GLS regression equations, giving projected central Rocky Mountains river discharges. These projections showed generally declining trends in central Rocky Mountains surface water availability for 2006-2050 and 2006-2096. This study's novel result is that projection distribution functions show a shift in the variance of the flows, from a relatively symmetric equal probability of low versus high flows about the mode and mean in 2006, to a broader, left-skewed flow pattern with a higher probability of low flows in general, and extreme low flows in particular, by 2096.