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| Colorado River Basin drought | |
|---|---|
| Name | Colorado River Basin |
| Caption | Map of the Colorado River watershed and major reservoirs |
| Location | United States; Mexico |
| Length | 2330 km |
| Basin countries | United States, Mexico |
| Discharge | variable |
Colorado River Basin drought The Colorado River Basin drought describes a prolonged period of reduced streamflow and water storage affecting the Colorado River watershed that supplies parts of the Southwestern United States and northwestern Mexico. The basin encompasses major infrastructure such as Hoover Dam, Glen Canyon Dam, and Lake Powell, and supports metropolitan areas including Los Angeles, Phoenix, Las Vegas, Denver, and Salt Lake City. Multiple agencies and compacts—most notably the Colorado River Compact of 1922—govern allocation among basin states and Mexico Treaty of 1944 obligations, making hydrology and policy tightly interwoven.
The Colorado River originates in the Rocky Mountains of Colorado and traverses the Colorado Plateau and Grand Canyon before reaching the Gulf of California in Mexico. Major tributaries include the Green River, Gunnison River, San Juan River, and Little Colorado River. High-elevation snowpack in the Upper Colorado River Basin——measured by the SNOTEL network and Natural Resources Conservation Service reports——drives seasonal runoff that fills reservoirs like Lake Mead and Lake Powell. Evaporation from reservoirs, groundwater interactions in the Lower Colorado River Valley, and consumptive uses by Central Arizona Project and Metropolitan Water District of Southern California play central roles in basin water budgets.
The basin has experienced variability driven by phenomena such as the El Niño–Southern Oscillation, Pacific Decadal Oscillation, and multidecadal trends in Atlantic Multidecadal Oscillation. Paleoclimate records from tree-ring reconstructions by researchers at institutions like the University of Arizona and NOAA document severe megadroughts during the medieval period comparable to or exceeding 20th-century dry intervals. Historical events include the late-19th-century drought and 1950s drought that stressed early reservoir operations and influenced development of projects under the Bureau of Reclamation and policies enacted by the United States Congress.
Since the late 1990s and particularly the 2000s, the basin has experienced persistent below-average flows, reduced Lake Mead and Lake Powell elevations, and record-low snowpack years. Scientists from United States Geological Survey and NASA attribute part of the decline to anthropogenic global warming documented by the Intergovernmental Panel on Climate Change and amplified by natural variability. Major operational milestones—such as the declaration of Tier 1 shortages under the 2007 Interim Guidelines and 2019 Drought Contingency Plans for the Lower Colorado River Basin—reflect the sustained nature and policy consequences of the ongoing drought.
Reduced river flows and reservoir storage have triggered cutbacks for Central Arizona Project, Imperial Irrigation District, and municipal suppliers like the Southern Nevada Water Authority and Metropolitan Water District of Southern California. Agriculture in the Imperial Valley and Central Arizona faces curtailed water deliveries, affecting producers represented by organizations such as the California Farm Bureau Federation and Arizona Farm Bureau Federation. Urban systems in Phoenix and Los Angeles have implemented conservation programs coordinated with state agencies like the Arizona Department of Water Resources and California Department of Water Resources while trading and water-banking arrangements involve entities including the Gila River Indian Community and various Colorado River Indian Tribes.
Ecosystems in the Grand Canyon and Upper Colorado River Basin have experienced altered flow regimes affecting native species like the Colorado pikeminnow and humpback chub. Reduced seasonal floods limit habitat rejuvenation for riparian vegetation such as cottonwood and willow communities; invasive species including Tamarix (saltcedar) and quagga mussel exacerbate ecological stress and infrastructure impacts. Wildlife agencies—like the U.S. Fish and Wildlife Service and state fish and wildlife departments—coordinate recovery and habitat conservation plans under statutes such as the Endangered Species Act.
Allocation of the river is governed by the Colorado River Compact, the Law of the River corpus, the Bureau of Reclamation, and agreements like the Minute 319 and Minute 323 with Mexico. Interstate coordination among Colorado River Basin states—Arizona, California, Nevada, Utah, New Mexico, Colorado, and Wyoming—and tribal nations such as the Pueblo of Zuni influences shortage-sharing, shortage declarations, and reservoir operations. Congressional policy, litigation in federal courts, and actions by entities such as the Western Governors' Association shape dispute resolution and long-term planning.
Responses include demand-management programs, urban conservation measures by agencies like the Metropolitan Water District of Southern California, agricultural efficiency upgrades supported by the Natural Resources Conservation Service, and market-based transfers facilitated by state water agencies. Infrastructure options under consideration involve modifications at Glen Canyon Dam and Hoover Dam, desalination projects in California and Mexico, and water reuse programs championed by utilities such as the Orange County Water District. Tribal water settlements, interstate compacts, and federal funding initiatives administered by the Bureau of Reclamation and Environmental Protection Agency form part of an adaptive portfolio aimed at increasing resilience to continuing hydrologic stress.
Category:Colorado River Category:Droughts in the United States