Introduction

A summary measure that provides information on the state of, or change in, the system being measured. Sometimes used interchangeably with metric, as in this report. See also Metric. Source: Fiksel et al. (2012).

The measured value(s) used to assess specific indicators. It defines the units and how the indicator is being measured. Sometimes used interchangeably with indicator. Source: Fiksel et al., 2012.

The area drained by the Colorado River and its tributaries; a hydrologic boundary including the combined areas of the Upper Colorado and the Lower Colorado Basins. When we use the term Colorado River Basin in this study, we refer to an area that differs slightly from the HUC-02 Region shapefiles in the USGS National Hydrography Dataset (see entry for Hydrologic Unit Code). We exclude some watersheds whose tributaries do not flow directly into the Colorado River, including the Great Divide Closed Basin (HUC ID: 140402) and several basins along the Arizona-Mexico border that flow directly into the Sea of Cortez (e.g., Río Sonoita and Río Concepción). We also include a few areas that are not in the HUC-02 Region footprints of the Upper or Lower Colorado within the National Hydrography Dataset, most notably the areas around the Salton Sea and Laguna Salada in Mexico. The Colorado River, like all rivers, shifts over time. Before Hoover Dam closed, the Lower Colorado would migrate wildly and often swung westward to feed directly into the Salton Basin, hence we include that area as part of the Colorado River Basin rather than within the Adjacent Areas Served. For more, explore the Babbitt Center’s map of the Colorado River Basin.  

Transbasin diversions, also called interbasin transfers, are man-made conveyance schemes which move water from one river basin where it is available, to another basin where water is less available or could be utilized better for human development. Source: Interbasin transfer - Wikipedia.

Short for adjacent areas served by Colorado River water. It refers to locales outside the hydrologic basin of the Colorado River, where its waters are exported via transbasin diversions. Most of the population that relies on Colorado River water lives in large cities in the Adjacent Areas Served, such as Denver, Los Angeles, and San Diego. The Adjacent Areas Served, as defined in this report, generally correspond with the “adjacent areas that receive Colorado River water” as defined by the U.S. Bureau of Reclamation (2012), with two notable differences. One is the watershed of the Salton Sea, a portion of which is classified as an adjacent area by the Bureau of Reclamation because it receives Colorado River water via the All-American Canal and Colorado River Aqueduct but no longer contributes tributary flow to the river. However, before Hoover Dam was built, the Colorado River would sometimes migrate from its current channel and into the Salton Sink (see, e.g., Ross 2020). Because of that connection, we include it within the hydrologic CRB area, rather than in Adjacent Areas Served. See U.S. Bureau of Reclamation, 2012, p. ES-3. The second exception is the area in northwestern Mexico encompassing the cities of Tijuana and Ensenada. Colorado River water is exported to Tijuana via the Colorado River-Tijuana aqueduct. For our purposes this counts as an AAS, but since it is a Mexican infrastructure project, it is not included in Bureau of Reclamation service area maps. The city of Ensenada is included in this area because Tijuana sends Colorado River water there via a pipeline that was originally constructed to pump water in the opposite direction. Although in our map this area may appear contiguous with the Southern California AAS that includes San Diego and Los Angeles, it is not part of the same service area on account of the international border.

This is the combined area of the hydrologic Colorado River Basin boundary (see CRB definition for exceptions) and the Adjacent Areas Served via transbasin diversions (see AAS definition). The CRBAAS had an estimated population of 43 million people in 2021.    

The Cornell Law School Legal Information Institute states: "Beneficial use is a term most commonly associated with water rights in the western United States and the prior appropriation doctrine. Many state statues describe beneficial use as the basis, measure, and limit of a water right. Because these states define water sources as public resources, non-riparian land owners can acquire a right to the use of a water source when they put its water toward beneficial use. However, the extent of their right is limited by the beneficial use..." Source: beneficial use | Wex | US Law | LII / Legal Information Institute (cornell.edu). 

The doctrine that the first person to take a quantity of water from a water source for "beneficial use" (agricultural, industrial or household) has the right to continue to use that quantity of water for that purpose. Subsequent users can take the remaining water for their own use if they do not impinge on the rights of previous users. Prior appropriation rights do not constitute a full ownership right in the water, merely the right to withdraw it, and can be abrogated if not used for an extended period of time. Source: Prior-appropriation water rights - Wikipedia.