Adaptation Planning to Improve Resiliance Against Extreme Weather Events - Sonoma County Water Agency Case Study

The Sonoma County Water Agency (SCWA) is working to improve the resilience of the water resources it manages in addition to its water supply facilities to withstand extreme weather events, specifically floods and droughts.  Located in northern California, SCWA is a Special District established by the California Legislature with responsibilities for flood control, wholesale water supply, sanitation, and energy generation.  This diverse portfolio of core responsibilities provides SCWA with opportunities to pursue integrated resource management, a key strategy for adaptation planning.  Other key strategies employed by SCWA include promoting a strong scientific basis for policy development and management decisions; and forming strategic partnerships to implement various adaptation initiatives and programs.  

The SCWA provides potable water on a wholesale basis to several cities and water districts comprising about 600,000 customers in Sonoma and Marin Counties in California.  SCWA’s primary source of supply is derived from its riverbank filtration (RBF) facilities along the Russian River.  SCWA and the U.S. Corps of Engineers co-operate two reservoirs on the river system for water supply and flood control, respectively. Similar to most water utilities, SCWA faces several challenges in continuing to provide reliable high quality potable water to its customers at the lowest possible cost to ratepayers.

While providing numerous benefits in terms of water quality and cost, SCWA’s RBF facilities are imbedded into the natural river system more than conventional treatment facilities are and are therefore highly reliant on the health of the watershed and river system. The Russian River watershed also has three species of salmonids listed at threatened or endangered under the Endangered Species Act (ESA).  The operation of water supply and flood control facilities must address impacts to salmonids and comply with the requirements of the ESA.  In addition, Sonoma County exhibits some of the highest repetitive flood damages in California, and is also prone to prolonged droughts.   Recent research by the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS) help explain the occurrence of these extreme weather events.   These studies have found that this region of the west coast of the U.S. experiences a high proportion of extreme storm events known as atmospheric rivers (ARs).  These narrow bands of extremely high moisture content water vapor extend from the equator across the Pacific Ocean.  When ARs hit landfall, they often result in intense volumes of precipitation focused in a narrow geographic area.  Because of the narrow width of ARs, while one area can experience extreme rainfall, another nearby area (perhaps as close as 100 kilometers away) may have dry weather.   The result is a tendency to experience either high rainfall –flood events or droughts, depending on the occurrence of ARs.

In addition, the effects of climate change are likely to increase the impacts of these weather events.   Downscaled climate modeling by the USGS indicates that in the future the region is likely to experience increased temperatures and variability of rainfall (i.e., more severe flooding and droughts).  Increased temperature will increase potable and agricultural water demand and evapotranspiration.  Soil moisture is also predicted to decrease, thus reducing recharge of groundwater aquifers. 

To address these challenges and to ensure reliable water resources to meet current and future needs, SCWA is pursuing the following strategies:

• Investing in science to provide the strongest understanding possible regarding the climate/weather, hydrology/hydrogeology, and ecology and to promote the use of this knowledge in management decisions and policy development.  
• Developing partnerships (e.g., federal, state, local government, community/stakeholder groups, private foundations) that leverage organization jurisdictions, staff and funding resources, and expertise to tackle regional water resource challenges. 
• Promoting integrated water resource management to improve the resiliency of regional water resources, increase the adaptability and efficiency of water management operations, and maximize funding opportunities.