Making better early-season water management decisions begins with enhanced streamflow forecasts

Research from Reclamation's Science and Technology Program seeks innovative solutions to water and power challenges in the western United States

Written by: Peter Soeth

The Rio Grande north of Santa Fe, New Mexico.While spring turns to summer in the West and snowmelt fills the streams and rivers, the Bureau of Reclamation and the National Center for Atmospheric Research have been collaborating on research that could improve the seasonal streamflow forecasts that form the basis of Reclamation’s early-season water management decisions.

Reclamation and NCAR have also been working with agencies that provide streamflow forecasts, including the Natural Resources Conservation Service and National Oceanic and Atmospheric Administration to incorporate this research into their annual forecast products. This work has focused on two major river basins that have their headwaters in Colorado, the Colorado River and the Rio Grande, but the results may be applicable throughout the western United States.

"Enhanced seasonal streamflow forecasts will improve Reclamation’s ability to make informed water-management decisions earlier in the season, and therefore improve our ability to meet the needs of our customers," Chief of Research and Development Levi Brekke said.

The first phase of this study found that recent declines in the amount of streamflow that is derived from a given amount of snowpack in the mountains were partly attributable to a trend toward warmer temperatures in the basins. This warming trend has been causing the statistically-based forecasts developed each year by the NRCS, which are based on past runoff efficiency relationships, to overpredict streamflow, especially during low-snowpack years. Simulations using climate models that have been initialized using current earth-system observations provide reasonably robust seasonal temperature forecasts. The researchers have therefore been collaborating with the NRCS to incorporate monthly to seasonal temperature forecasts from a suite of models. These results have shown moderate improvement in seasonal water supply forecasting.

Collaboration is ongoing with the NRCS to implement this approach into their operational forecasting workflows. A follow-on collaborative project between Reclamation and NCAR builds on this and other NCAR forecasting work to expand the forecasting approach to other basins in the western United States. This follow-on project is also working with the Colorado and West Gulf River Forecast Centers to develop and enhance Ensemble-Streamflow-Prediction-based forecasts for the Rio Grande and then incorporate those forecasts, along with the NRCS forecasts, into the Upper Rio Grande Water Operations Model and the annual operating plans developed using that model.

"Incorporation of temperature forecasts for the coming months promises to improve the skill of statistical streamflow forecasts, therefore allowing Reclamation to make better water management decisions," lead researcher Dagmar Llewellyn added. "We are excited to implement the results of this research into our annual operating plans for the upper Rio Grande."

This research was funded by Reclamation's Science and Technology Program. It is a Reclamation-wide competitive, merit-based applied research and development program. The program focuses on innovative solutions for water and power challenges in the western United States for Reclamation water and facility managers and the stakeholders they serve. Learn more at https://www.usbr.gov/research/st.

Runoff Efficiency and Seasonal Streamflow Predictability in the U.S. Southwest

Published on June 24, 2019