Water Governance in an Era of Climate Change: A Model to Assess the Shifting Irrigation Demand and Its Effect on Water Management in the Western United States

Communities throughout the United States have come to rely upon agriculture as a pillar of their political integrity, economic security, and health and wellbeing. Climatic conditions in the western portion of the United States necessitate most lands be irrigated to be arable. As a result, a major portion of the economy of the United States, and by extension the world economy, is driven by the continued viability of western United States water law and policy. Furthermore, due to the strong interrelationship between anthropogenic consumptive uses, streamflows, and wetland/riparian area ecology, irrigation demand has a strong effect on stream morphology, quality, and biology for aquatic species. Western water management is a complex mosaic that is controlled by western state, federal, and tribal governments. Each of these systems of law have vulnerabilities to climate change, which is well understood to cause increasing water supply scarcity. This articledemonstrates the risks climate change poses to our management of irrigation water demand, as well as the interrelationship between water supply and demand. Due to the shared nature of the resource, this article addresses both tribal reserved rights and state-based rights using data from Indian reservations that either contain and/or are closely adjacent to non-tribal agricultural communities. Those data are used in a systems-dynamics model to integrate crop-water requirement estimation techniques with climate change estimates and a Monte Carlo analysis to assess how irrigation demand could change because of changing temperature, precipitation, incoming radiation, and wind speed caused by climate change. Results indicate that climate change will cause increases in irrigation requirements at most locations. Further, climate change is expected to significantly increase seasonal variability in many locations. The model provides a useful tool based upon publicly available data that will allow individual water users to make conservation decisions necessary to preserve their water rights as the climate changes.