Tensions and Cooperation
The legal and institutional framework for water allocation in the western United States creates the basis for tensions during droughts by establishing a "zero-sum" game, where some water users have highly reliable water rights and others lose access to water completely. Water allocation in the western United States is governed by the principle of prior appropriation and beneficial use, known colloquially as "first in time, first in right" and "use it or lose it," respectively. During drought periods, the first to establish and maintain a beneficial use is the last to lose access. This principle applies at the level of water users and their associations (irrigation districts and municipal utilities). The Colorado River and Rio Grande illustrate the tensions and cooperation associated with transboundary management of droughts in the western US system of water allocation. In the US portion of both the Colorado and Rio Grande/Bravo, interstate water apportionment agreements exist to share water based on principles of equitable use between states. Each agreement defines allocation rules requiring the delivery of volumes of water from upstream to downstream states, creating coordination challenges during droughts.
In the Colorado River, drought conditions and competition for water have placed intergovernmental water agreements under pressure, exacerbating tensions stemming from the structural imbalance between demand and supply (i.e., the overcommitment of the river's annual renewable runoff). The 1922 Colorado River Compact and a series of additional laws, rules, court cases, and operational criteria constitute the Law of the River, apportioning water between the states sharing the river on the US side. Drought and shortage conditions were not addressed by this institutional framework, creating uncertainty about the operational criteria used to manage reservoirs and share shortages between states until recently, as discussed below. Tensions between states within the US portion of the river basin have produced a legacy of intense conflict over interstate water allocation matters, including the landmark 1963 Supreme Court case, Arizona v. California, which clarified and confirmed prior interstate accords. Despite the concerns and fears that severe sustained drought would trigger interstate conflict, the dry period since 2000 has been marked by unprecedented cooperation, culminating in a series of agreements and institutional mechanisms for building resilience to drought and water scarcity, including shortage sharing agreements that include Mexico and ongoing efforts to negotiate a drought contingency plan that would address severe shortages.
In the Rio Grande/Bravo, drought has exacerbated pressures related to urbanization and endangered species issues in the US portion and has caused both interstate and international tensions with Mexico. A complex set of intergovernmental agreements divide water between states in the United States (1938 Rio Grande Compact) and between countries (1906 Convention and 1944 Water Treaty). In the United States, drought since 2000 has heightened dependence on and conflict over groundwater pumping, with several interstate coordination challenges because of effects of groundwater pumping in Colorado on New Mexico's water supplies and effects of groundwater pumping in Southeast New Mexico on the reliability of water deliveries to Texas under the Rio Grande Compact. This dispute has prompted a court case between Texas and New Mexico that is currently before the Supreme Court.