Reclamation Information Sharing Environment (RISE)

Reclamation’s Yuma Area Office (YAO) in Yuma, AZ, manages the last stretch of the Lower Colorado River before it crosses the border with Mexico. YAO navigates the many complex dependencies on the river on a daily basis, from deliveries to regional irrigation districts to water quality and volume regulations under an international water treaty. Despite detailed accounting of water releases and diversions from upstream dams and water users, unexplained daily fluctuations in the amount water arriving in Yuma, termed ‘losses’ and ‘gains’, nonetheless occur. The unpredictable nature of these losses and gains complicates YAO’s operations. Thus, forecasts of losses and gains could be of value to YAO’s operations. Research Activities and Results: This project aimed at investigating the main causes of unexplained daily fluctuations of losses and gains in the reach between Parker Dam and Imperial Dam on the Colorado River and to develop tools to forecast them. Using existing observational records, the project confirmed the existence of loss and gain events that rise above the baseline variability. It was revealed that a significant backwater effect exists in the lower part of the reach, closely tied to the weekly release schedule at Parker Dam. After correcting for this backwater effect, major precipitation events were found to be responsible for the most significant gain events, but that smaller precipitation events are usually not detectable against the baseline variability. Precipitation forecast skill on 3-day timescales was found to be moderate, even after locally calibrating the precipitation forecasts. Consequently, loss-gain forecast skill based on precipitation forecasts remains low, although probabilistic forecasts based on ensemble calibration might still offer value for operations planning purposes.