Climatic Fluctuations and Forecasting of Streamflow in the Lower Colorado River Basin¹

Abstract

Water‐resource managers need to forecast streamflow in the Lower Colorado River Basin to plan for water‐resource projects and to operate reservoirs for water supply. Statistical forecasts of streamflow based on historical records of streamflow can be useful, but statistical assumptions, such as stationarity of flows, need to be evaluated. This study evaluated the relation between climatic fluctuations and stationarity and developed regression equations to forecast streamflow by using climatic fluctuations as explanatory variables. Climatic fluctuations were represented by the Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and Southern Oscillation Index (SOI). Historical streamflow within the 25‐ to 30‐year positive or negative phases of AMO or PDO was generally stationary. Monotonic trends in annual mean flows were tested at the 21 sites evaluated in this study; 76% of the sites had no significant trends within phases of AMO and 86% of the sites had no significant trends within phases of PDO. As climatic phases shifted in signs, however, many sites had nonstationary flows; 67% of the sites had significant changes in annual mean flow as AMO shifted in signs. The regression equations developed in this study to forecast streamflow incorporate these shifts in climate and streamflow, thus that source of nonstationarity is accounted for. The R2 value of regression equations that forecast individual years of annual flow for the central part of the study area ranged from 0.28 to 0.49 and averaged 0.39. AMO was the most significant variable, and a combination of indices from both the Atlantic and Pacific Oceans explained much more variation in flows than only the Pacific Ocean indices. The average R2 value for equations with PDO and SOI was 0.15.

El Niño Southern Oscillation link to the Blue Nile River Basin hydrology

“…Climatic prediction based on this correlation has become part of water management decision making (Obeysekera et al, 2007). Thomas (2007) developed regression equations forecasting Colorado River streamflow using climatic index as variables for application in water resource management. Discrete monthly climatic index as ENSO do not amplify the strength of the event.…”

Synthesis of ground and remote sensing data for monitoring ecosystem functions in the Colorado River Delta, Mexico

“…Furthermore, Colorado River flows are inherently variable (Thomas, 2007), and climate change is expected to decrease spills from the dams due to an overall drying trend in the watershed (Christensen and Lettenmaier, 2007). Additionally, the ecological value of the riparian corridor has been degraded by tree cutting, human-set fires, and vegetation clearing for flood control in Mexico (Nagler et al, 2005b).…”

“…The trees, in turn, are important elements in supporting avian habitat, even when saltcedar is the dominant plant species (Sooge et al, 2008;van Riper et al, 2008). The flows are related to ENSO cycles that increase the snowpack in the Colorado River watershed during El Nin o events, resulting in water releases from the U.S. dams in spring (Thomas, 2007). These releases are expected to diminish in the future due to effects of climate change on the watershed (Christensen & Lettenmaier, 2007).…”

Colorado River Basin Hydroclimatic Variability

“…nrcs.usda.gov/snow/about.html) sites across the western United States and various climate indices. Thomas (2007) studied Lower Colorado River basin (LCRB) flow ties to the same indices at seasonal and annual scales, for a variety of lead/lag times. Additionally, the cold phase of PDO, when compared with the warm, was found to correspond with reduced snowpack in similar regions.…”