Abstract
Author(s): Schwarz, Andrew Mark | Abstract: Climate change and resulting changes in hydrology are already altering—and are expected in the future to continue to alter—the timing and amount of water flowing through rivers and streams. As these changes occur, the historical reliability of existing water rights will change. This study evaluates future water rights reliability in the Sacramento–Feather–American river watersheds. Because adequate data are not available to conduct a comprehensive analysis of water rights reliability, a condition placed into certain water rights, known as Term 91, is used to model projected water rights curtailment actions. Comparing the frequency and length of the historical and simulated future water diversion curtailments provides a useful projection of water rights reliability and water scarcity in the Sacramento–San Joaquin Delta (Delta) watershed.Projections of future water rights curtailments show that water rights holders are likely to be curtailed much more frequently, and for significantly longer durations, as we move through the 21st century. Further, many more water rights holders will be affected by curtailment actions in the future. As curtailments last longer and become more common, more water users will have to access other supplies, such as groundwater or water transfers, or will have to fallow land or conserve water in other ways to meet their demands. These activities will likely ratchet up the potential for additional conflicts over water in the Delta watershed.
Highlights
Water rights form the core of California’s surface water resources system, and determine who may divert what quantity of water and when
By examining projected changes in hydrology over the 21st century, this study looks at how projected water availability will affect existing water rights holders in the Sacramento–Feather–American river watershed
Each of the six climate models used in the study project slightly different types of shifts in temperature and precipitation and each of the six models is run with an optimistic projection of greenhouse gas (GHG) emissions (Emissions Scenario B1) and a more pessimistic–realistic projection of GHG emissions (Emissions Scenario A2) in the future
Summary
Water rights form the core of California’s surface water resources system, and determine who may divert what quantity of water and when. When the calculation of SPW becomes positive (i.e., storage releases exceed diversions plus carriage water), the two conditions required to invoke Term 91 are met When this happens, typically in late spring or early summer, the Water Board issues curtailment orders to water rights holders subject to Term 91, requiring that they cease diverting water. Term 91 and the SPW calculation serve as a useful proxy metric for water shortages in the Delta watershed They provide a quantifiable metric over time that describes the degree to which releases from the Projects' storage facilities are needed to meet the water demands in the basin. The SPW calculation provides a useful metric to determine at what point each year natural flows in the Delta watershed become insufficient to meet the watershed’s water demands By tracking this date over time we can gauge how water availability may change in the future. Changes in Term 91 curtailments may provide information about other changes in water management and operations, and may foreshadow conditions that require additional curtailments on other water users not subject to Term 91, as has occurred during previous droughts
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