07 December 2018

The Changing Character of the California Sierra Nevada as a Natural Reservoir

Understanding how mountain snowpack may change upstream of California’s major surface reservoirs.

Science

The historical role of California’s Sierra Nevada mountain snowpack as a steady source of fresh water will fade due to climate change. In this paper we aim to answer four major questions surrounding the regional spatiotemporal change in Sierra Nevada mountain snowpack such as how it may change in the headwater regions of major surface reservoirs, the latitudinal and elevational dependencies of this change, and how the choice of regional climate model influences future projections.  These questions are answered using a use-inspired multi-metric framework developed through ongoing scientist-stakeholder interaction in Project Hyperion and applied on a multi-model ensemble the North American Coordinated Regional Climate Downscaling Experiment (NA-CORDEX).  

Impact

The California Sierra Nevada acts like a natural water tower that stores snowpack in winter and releases it as snowmelt during spring to summer. However, climate change has and continues to undermine this natural service. This work provides detailed guidance on the mountain snow conditions policymakers, water managers, and scientists will encounter in addressing adaptive resiliency for California’s water supply system. Under a high-emissions scenario, a 79.3% decline in peak snow upstream of nearly half of California’s surface reservoir storage is shown by end century. Across nine regional climate model simulations historical snow representation varied but by end century regional climate models agree on the magnitude and direction of decline. 

Summary

Mountains are natural water towers that store snowpack in winter and release it as snowmelt during spring to summer. However, climate change has and continues to undermine this natural service. To answer where and when water resource management may be impacted by a future of low-to-no snowpack, we can leverage climate models, which are able to project the future conditions of mountain snowpack under various assumptions of global greenhouse gas emissions. In this study, we use five unique climate models under a high-emissions scenario to evaluate a set of snowpack measures upstream of 10 California reservoirs. These 10 reservoirs represent nearly half of California’s surface storage and by the end of the century, could face a 79% reduction in peak snowpack water volume. The largest reductions are above Shasta, Oroville, and Folsom and between 0- and 2,000-m elevations.  This work provides detailed guidance on the mountain snow conditions policymakers, water managers, and scientists will encounter in addressing adaptive resiliency in the face of climate change.

Contact
Andrew D. Jones
Lawrence Berkeley National Laboratory (LBNL)
Publications
Rhoades, A, A Jones, and P Ullrich.  2018.  "The Changing Character of the California Sierra Nevada as a Natural Reservoir."  Geophysical Research Letters, doi:10.1029/2018gl080308.