Exploring the use of temperature to understand recent drought and project future conditions in the Colorado River Basin
How can a combination of historical hydrologic data, decadal temperature predictions, and longterm temperature projections help to:
1. Provide insights about the ongoing CRB drought and recent shifts in basin efficiencies?
2. Improve midterm CRB streamflow and operations projections?
3. Characterize conditions to which the CRB system is most vulnerable? and
4. Clarify the credibility of future climate projections derived from GCMs?
Need and Benefit
Need: In order to provide reliable information to stakeholders about potential water supply risks in the CRB,
Reclamation needs to project midterm streamflow and reservoir operations as accurately as possible. Despite being in
the midst of a historic drought, Reclamation continues to use midterm projections that do not have skill beyond that
provided from climatology. Recent studies have shown warm temperatures have reduced streamflow periodically
throughout the observed record (Woodhouse et al., 2016) and that recent decades have shown a significant trend of
temperature-induced streamflow declines (McCabe et al., 2017), but this information has not yet been incorporated
into midterm projections. Newly-developed methods to predict midterm temperatures offer an avenue for incorporating
temperature information (Towler et al., 2018), but there is still a need to research the potential for operationalizing
Benefit: This project will systematically characterize and assess the available sources of CRB temperature
information, resulting in a more organized view of the data that Reclamation has produced or collected over the
course of multiple projects. The in-depth analysis of the observed record will increase Reclamation's understanding of
how basin efficiencies may have shifted during the ongoing drought and how they may continue to shift. The
evaluation of the different ensembles will result in experimental projections that demonstrate the utility of the CRB
Projection Testbed, which was recently developed within Reclamation. Skillful midterm projections can provide a more
accurate view of potential risks to the CRB system. This project is notably beneficial as an early test of the usefulness
of decadal temperature predictions in practice; the results will be widely interesting, even beyond Reclamation. Finally,
there is little guidance on how to interpret CRB climate projections derived from GCMs, and this work will clarify the
relationships between observed, midterm, and longterm temperature and basin efficiency information.
While CRB-focused, the successful implementation of the project will demonstrate the framework's potential to be
extended to other regions across Reclamation.
Urgency: The ongoing historic CRB drought underscores the importance of identifying recent and future midterm
trends. Now that Lakes Powell and Mead are near critical elevation thresholds, any improvement in projecting
elevations 2- to 5-years out will be highly valuable for helping stakeholders avoid or prepare for shortages.
Improvements in Reclamation's ability to characterize future streamflow and risk would also contribute to modeling in
support of upcoming renegotiations of the Interim Guidelines for Lower Basin Shortages and the Coordinated
Operations for Lake Powell and Lake Mead, which will begin no later than 2020 (Interim Guidelines).
Contact the Principal Investigator for information about partners.
Contact the Principal Investigator for information about these documents.