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| Second Colorado River Basin Study | |
|---|---|
| Name | Second Colorado River Basin Study |
| Formation | 2023 |
| Purpose | Long-term water-resource planning for the Colorado River |
| Headquartered in | Bureau of Reclamation headquarters, Washington, D.C. |
| Region served | Upper Colorado River Basin, Lower Colorado River Basin, Colorado River Delta |
| Parent organization | United States Department of the Interior |
Second Colorado River Basin Study
The Second Colorado River Basin Study was a comprehensive, multiagency assessment initiated to update basin-scale projections for the Colorado River system and to recommend operational and policy responses for the Bureau of Reclamation, Department of the Interior, Secretary of the Interior, and basin states including Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming. Convened after prolonged drought and declining Lake Powell and Lake Mead elevations, the study synthesized climate science, hydrology, and legal frameworks such as the Colorado River Compact and Boulder Canyon Project Act to inform federal, state, tribal, and municipal water managers.
The study built on precedent studies including the 1970s Colorado River Basin Project analyses and the 2007 Bureau of Reclamation Colorado River Basin Water Supply and Demand Study, responding to altered hydrology observed since the 2000s North American drought and projections from agencies such as the National Oceanic and Atmospheric Administration, United States Geological Survey, and the National Aeronautics and Space Administration. Mandated in coordination with the Seven Basin States and tribal nations like the Navajo Nation and Ute Mountain Ute Tribe, the study aimed to reconcile water allocation under the Law of the River, protect deliveries to users in Mexicali and the Colorado River Delta, and address obligations under the Minute 319 and Minute 323 agreements with Mexico. It sought to inform operations at federal facilities including Hoover Dam, Glen Canyon Dam, and Davis Dam.
Analytical frameworks integrated outputs from global and regional climate models such as the Coupled Model Intercomparison Project ensembles and the North American Regional Climate Change Assessment Program. Hydrologic modeling used datasets from the Hydrology Laboratory–Research branch at the USDA Agricultural Research Service and streamflow records from the U.S. Geological Survey (USGS). Evapotranspiration and snowpack analyses incorporated remote sensing products from NASA MODIS and the Landsat program and in-situ observations from the Natural Resources Conservation Service (NRCS)]’s SNOTEL network. Water-use and demand projections drew on municipal reports from Los Angeles Department of Water and Power, Metropolitan Water District of Southern California, Central Arizona Project, and agricultural consumption data compiled by the United States Department of Agriculture (USDA). Legal and institutional review referenced texts of the Colorado River Compact of 1922, the Arizona v. California adjudication, and interstate memoranda such as the Drought Contingency Plan (2019). Stakeholder engagement included consultations with tribal governments, the Western Governors' Association, environmental NGOs like The Nature Conservancy, and industrial water users represented by groups such as the Association of California Water Agencies.
The study reported statistically significant trends of reduced mean annual inflow to Lake Powell and Lake Mead driven by rising temperatures and reduced snow-to-rain ratios consistent with Hadley Centre-derived projections and CMIP6 scenarios. Under mid-range emissions trajectories (analogous to SSP2-4.5), modeled median flows declined compared with 20th-century baselines; under high-emissions pathways (analogous to SSP5-8.5), declines were larger, accelerating risk of shortage declarations under the 1978 Coordinated Operations Agreement and triggering lower basin shortage tiers affecting Central Arizona Project deliveries and Colorado River Indian Tribes allocations. Projections highlighted increased frequency of critically low elevations at Glen Canyon Dam and Hoover Dam, elevated evaporation losses from reservoirs, and altered seasonality reducing peak spring runoff historically supplied by Rocky Mountains snowmelt.
Recommendations combined supply augmentation, demand reduction, and governance reforms. Supply-side options included managed aquifer recharge projects in the Sonoran Desert and Salton Sea region, increased water banking through entities such as the Metropolitan Water District of Southern California, and targeted fallowing programs modeled on Arizona's Intentionally Created Surplus framework. Demand-side measures emphasized conservation codes adopted by City of Phoenix, advanced irrigation efficiency in agricultural districts like the Imperial Irrigation District, and urban pricing reforms observed in Denver Water and Las Vegas Valley Water District practices. Institutional proposals urged revisions to shortage allocation under the Law of the River, enhanced tribal water settlements like those negotiated with the Tohono Oʼodham Nation, and expanded binational mechanisms with Comisión Internacional de Límites y Aguas and CONAGUA to operationalize flexible delivery arrangements similar to Minute 319/Minute 323.
The study detailed differentiated impacts across sectors and jurisdictions: rural agricultural communities in the Imperial Valley and Yuma County, Arizona faced high exposure to reduced allocations; urban centers including Phoenix, Las Vegas, and Los Angeles showed capacity to implement aggressive conservation but required complex reallocations with agricultural partners; tribal nations emphasized water rights recognition and infrastructure funding; environmental advocates pressed for protections for Colorado River Delta riparian habitat and endangered species such as the humpback chub and Southwestern willow flycatcher. Responses ranged from endorsement by state water agencies and utilities to legal challenges by irrigation districts and contentious legislative debates in state capitols such as Sacramento, Phoenix (capital), and Denver.
Implementation pathways proposed phased actions over 5–30 years with pilot programs in reservoir operations, demand-management incentives, and tribal infrastructure investments. Funding sources recommended included federal appropriations via the Bipartisan Infrastructure Law, competitive grants from the Bureau of Reclamation WaterSMART program, state bond measures such as those in California Proposition 1 (2014), and public–private partnerships involving utilities like Salt River Project. Timelines prioritized near-term emergency shortage mitigation measures, medium-term infrastructure and legal reform, and long-term adaptive governance conditioned on iterative reassessments using updated NOAA and USGS monitoring.
Critics noted reliance on climate model ensembles with intrinsic uncertainty cited by scholars at Stanford University and University of Arizona and questioned assumptions about future demand elasticity referenced by economists at University of Colorado Boulder. Limitations included sparse hydrometeorological station density in headwater basins, incomplete accounting for groundwater-surface water interactions in portions of the Upper Colorado River Basin, and legal constraints under the Law of the River limiting rapid reallocation. Subsequent investigations by institutions such as Lawrence Berkeley National Laboratory and Scripps Institution of Oceanography have advanced integrated sociohydrologic modeling and updated projections incorporating recent megadrought episodes, while ongoing tribal-led studies are clarifying infrastructure needs for water delivery and storage.