Predicting Flow Volumes in the Upper Colorado River Basin during Three Climate Cycles of the 20th Century Using Sep-Mar Complementary Temperature and Precipitation Patterns

Efficient and effective use and management of available water resources depend on accurate and timely forecasts. Variability in climate and hydrology is a consequence of natural causes and human activities, including large-scale ocean/atmosphere interactions (Hegerl et al., 2007); variations in the solar cycle (Meehl and Arblaster, 2009), climate change (e.g., Pagano and Garen, 2005; Garfin et al., 2008), and modifications to land use and land cover (Milly et al., 2008). Hydroclimatic variability increased over the 20th Century, so it is therefore critical to understand the underpinnings of hydroclimatic variability. Climate cycles are a fundamental form of hydroclimatic variability, and are shaped by large-scale ocean/atmosphere interactions, or climate modes, that influence hydroclimate in a region, and are affected by natural and anthropogenic external forcings. Prevailing temperature and precipitation conditions (e.g., cool/wet or warm/dry) lasting approximately 25-30 years characterize climate cycles, and they change with variations in the climate modes (McCabe et al., 2008). In the Colorado River Basin (CRB), climate modes which influence hydroclimate and shape climate cycles include the Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and El Niño/Southern Oscillation (ENSO). Three climate cycles occurred in the CRB during the 20th Century. Results of applying the methodology to the upper Yampa and Gunnison river basins demonstrate that complementary temperature and precipitation conditions accompany wetter or drier conditions on climate cycle and annual scales, and that complementary conditions may be utilized for purposes including improving accuracy and increasing lead time of water supply forecasts.