Evaluating the Influence of Precipitation, Temperature, and Soil Moisture on Upper Colorado River Basin Streamflow and Drought

Wednesday, 17 December 2014: 9:30 AM
Connie A Woodhouse, University of Arizona, Tucson, AZ, United States, Stephanie A McAfee, University of Nevada Reno, Reno, NV, United States, Gregory J McCabe Jr, USGS, National Research Program, Lakewood, CO, United States, William P Miller, NOAA Colorado Basin River Forecast Center, Salt Lake City, UT, United States and Gregory T Pederson, U.S. Geological Survey, Bozeman, MT, United States
In the upper Colorado River basin (UCRB), cool season (October-April) precipitation in the form of snowpack is the most critical factor determining water year runoff, but other climatic factors can also play an important role. In this study, we examine how antecedent soil moisture conditions, spring temperatures, and total cool season precipitation can influence upper Colorado River streamflow, particularly during periods of low flow. First, we evaluate the contributions of these three variables during six major droughts in the UCRB, contrasting the relationships between precipitation, temperature and antecedent soil moisture over these periods. Next, we assess relationships between annual natural flow and cool season precipitation to identify anomalous years when flow is low, but precipitation is above average and when precipitation is low, but flow is above average to determine if temperatures or antecedent soil moisture could influencing these anomalies. Finally, we calibrate a multiple linear regression model to assess the contributions of the three variables in explaining water year streamflow. Models with and without the soil moisture variable are compared to better understand under what conditions this variable may be most influential to streamflow. Preliminary results indicate that spring temperatures are an important factor contributing to low flows, and this may have been most important during the 2000s drought. In a small number of years, it appears that spring temperature and/or antecedent soil moisture can ameliorate the influence a dry winter, or conversely, override wet conditions to result in below average streamflow. In the regression, cool season precipitation explains 66% of the variance in water year runoff. March-July temperature adds 8%, and November soil moisture just 2% explained variance. The contribution of soil moisture appears to be most important to streamflow in years with moist antecedent conditions.