WSC Category 3: Propogating Climate-Driven Changes in Hydrologic Processes and Ecosystem Functions across Extreme Biophysical and Anthropogenic Gradients

University Of California - Merced, Merced CA

Investigators

Abstract

1204841 Harmon In many arid and semi-arid regions of the world, including much of Western U.S., water resources management plans are predicated on the assumption that the snow pack holds the majority of the water, gradually melting to replenish the reservoirs as their supplies are metered out to satisfy human water and power demands, and environmental flow mandates. Nowhere is this more evident than in the Sierra Nevada Mountains in California, the remote and sparsely populated mountain range providing the water and power for millions of people. While it is known that this mountain range's steep gradients in elevation, soils and vegetation render it extremely sensitive to climate change, the connection between the underlying hydrologic processes and the water sustainability issues in these regions is not well understood. This project will quantify the effect of a range of documented climate change scenarios on snow melt, runoff, high elevation reservoir operation (hydropower, flood control and recreation) and low elevation multi-purpose reservoir operation (irrigation, flood control, environmental flows and recreation). The San Joaquin River Basin will serve as the prototype for this study, the outcomes of which will be transferrable to other snowpack-controlled river basins. The scientific goal of the proposed project is to connect our emerging process-level understanding of climatic influences on mountain hydrologic processes and resulting changes to the stream response to the ecosystems services sustained by water but dictated by human values and policies. The hypothesis is that changing climate variability in the semi-arid western U.S., and the resulting shift toward an earlier annual runoff in snow-dominated watersheds will create a ripple effect, propagating down the mountain front to force human responses in the form of changes to high elevation hydropower and lowland water supply reservoir operations, and therefore changes to lowland aquatic and riparian ecosystem functions. We will test this hypothesis using current hydrologic process simulation models integrate existing data from the NSF Southern Sierra Critical Zone Observatory, and from state (California Department of Water Resources) and federal agencies (U.S. Bureau of Reclamation, U.S. Fish and Wildlife Service). These simulation models will be driven by archival Global Climate Model (GCM) outputs (temperature, precipitation) for the years 2010 - 2099. This project will clarify the connection between likely climate change scenarios, stream flows, reservoir storage and releases, and groundwater storage and extractions for snow-dependent river basins. Furthermore, through engagement with key river basin stakeholders, the project will result in practical guidelines to how best to adapt policy to the changing hydrologic conditions in order to sustain water supply, energy and aquatic ecosystem needs in the future. The San Joaquin River basin was selected as the subject of study because it embodies water and sustainability issues in the semi-arid West given (1) its vulnerability to climatic variation due to its reliance on snow pack and a network of reservoirs for hydropower, flood control, and water supply; and (2) its massive lowland river salmon restoration effort, which was initiated in Fall 2009.