An Assessment of Potential Severe Droughts in the Colorado River Basin

Abstract

Much has been learned about Colorado River hydrology since the severe sustained drought study in 1995. We summarize our updated understanding of plausible future drought conditions by considering historical flows, tree‐ring reconstructions, and climate change. We focus on natural streamflow at Lees Ferry, the primary metric used to quantify the runoff in the Colorado River Basin. We identify drought periods using historical records and tree‐ring reconstructed streamflow at Lees Ferry, which we then use to characterize potential future droughts. Resampling from past drought periods generates plausible future conditions to consider during planning. We produced three drought scenarios, each comprising 100 streamflow sequences to be used as input to systems operation and management models. We used analysis of the duration‐severity and cumulative deficit relative to the mean natural flow to evaluate droughts and drought simulations and show that the current millennium drought that started in 2000 has an average flow far less than the historical record. However, the flows reconstructed from tree rings or future flows projected from climate models indicate that even more severe droughts are possible. When used as input to the Colorado River Simulation System the drought scenarios developed indicate considerable periods when Lake Powell falls below its hydropower penstocks, indicating a need to rethink management and operation of these reservoirs during these critical conditions.

Featured Collection introduction: Severe sustained drought revisited managing the Colorado River system in times of water shortage 25 years later—Part II

“…The call for papers for the JAWRA Featured Collection: Severe Sustained Drought Revisited: Managing the Colorado River System in Times of Water Shortage 25 Years Later led to more insights than could fit into a single issue. This second set of articles highlights the work done by Salehabadi et al (2022) on three historically based drought scenarios, McCoy et al (2022) on explaining seven climate‐related extreme events of greatest interest to water managers, Colby and Hansen (2022) on urban water demand management and policies for improving water supply reliability, Garcia‐Hernandez et al (2022) on water quality in the Colorado River Delta, and Ayres et al (2022) on economic losses from reducing inflows into the Salton Sea. These papers, alongside the first set of articles (see overview in Frisvold et al, 2022), continue to illustrate the range of challenges and the expertise applied to them in thoughtful, innovative, and multi‐disciplinary ways.…”

“…In addition to these concerning issues, there is a growing consensus that warming from climate change will reduce future runoff of the Colorado River Basin. Salehabadi et al (2022) warn that climate change could be associated with megadroughts even more severe than those quantified in their study.…”

“…The article by Salehabadi et al (2022) quantifies the impacts of three drought scenarios based on three past sustained droughts. The earliest-documented in tree-ring data-occurred from 1576 to 1600 and served as the basis for the original Severe Sustained Drought (SSD) analysis.…”

Evaluation of the ERA5‐Land Reanalysis Data Set for Process‐Based River Temperature Modeling Over Data Sparse and Topographically Complex Regions

“…The result of these changes, as well as the introduction of nonnative competing species, have been a decline and in some cases extirpation of endemic fish species (Bestgen & Hill, 2016; Dibble et al., 2021; Gloss & Coggins, 2005; Martinez et al., 2014; Olden et al., 2006). As the basin continues to grapple with the ongoing Millennium Drought (2000–present; Salehabadi et al., 2020; Wheeler et al., 2021) and the reduction of flows due to a warming climate (Dettinger et al., 2015; Udall & Overpeck, 2017), reservoirs have fallen to unprecedented low levels. If reservoir elevations, thermal stratification patterns, or operational procedures change significantly, the downstream river segments and ecosystems may once again be altered (Null et al., 2013).…”

Select Water Quality Parameters during Wet and Dry Conditions in the Colorado River Delta

“…A report from the Center of Colorado River Studies (Salehabadi et al. 2020) indicates that the current “millennium” drought that began in 2000 has resulted in an average flow that is far less than that of the average the natural flow record, which is available from the U.S. Bureau of Reclamation and dates back to 1906. Given that the likelihood of severe droughts is expected to progressively increase, hotter and drier conditions are also likely to further affect the ecosystems of the CRD.…”