U.S. Geological Survey (USGS) scientists and academic colleagues have found that, by 2099, global climate change will cause shifts in and destruction of biological communities, rising sea levels, and diminished water supplies on the U.S. West Coast – and specifically in the San Francisco Estuary-Watershed, which includes San Francisco Bay, the Sacramento-San Joaquin Delta (Delta) and the Sacramento and San Joaquin river drainages (the Bay-Delta system).
The San Francisco Estuary-Watershed (SFEW) has social and economic significance as the source of runoff that provides drinking water to 25 million people and irrigation water to 2.8 million acres of farmland, producing crops valued at $36 billion per year. On the shores of this estuary, 270,000 people and $62 billion of development are at risk of flooding as sea level continues to rise.
The SFEW also has major ecological significance because:
- The Sacramento and San Joaquin river system is a habitat for native fish, including Pacific salmon and steelhead trout;
- San Francisco Bay is the largest estuary on the U.S. West Coast, serving as a habitat for endemic species, such as the delta smelt and the salt marsh harvest mouse, as well as marine species supporting fisheries (e.g. English sole, Dungeness crab); and
- Fourteen species of migratory or Delta-resident fish also are imperiled.
According to the researchers, to date, California's hydrology has followed the climate-driven patterns of change observed across the western United States and attributed to human-induced warming. These patterns include trends of increasing winter and spring air temperatures and lengthened growing seasons, decreasing contributions of snow to annual precipitation, and advancement of spring snowmelt by 5 to 30 days. Mean sea level at the entrance to San Francisco Bay has increased about 2.2 cm (almost an inch) per decade since the 1930s, and the frequency of extreme tides has increased 20-fold since 1915.
In future climate scenarios for the California region, in which air temperatures have been projected to increase 1.5° to 4.5°C (about 3° to 8°F), anticipated responses include:
Therefore, the researchers predict that climate-driven changes to the SFEW could require resident human, animal, and plant species to adapt to “a diminishing water supply, continued shifts toward wetter winters and drier summers, sea level rising to higher levels than were projected only a few years ago, salt water intrusion, reduced habitat quality for native aquatic species, and expanding envelopes of environmental variability into regimes we have not yet experienced.”
“The protection of California's Bay-Delta system will continue to be a top priority for maintaining the state's agricultural economy, water security to tens of millions of users, and essential habitat to a valuable ecosystem,” said USGS Director Marcia McNutt. “This new USGS research complements ongoing initiatives to conserve the Bay-Delta by providing sound scientific understanding for managing this valuable system such that it continues to provide the services we need in the face of climate uncertainty.”
Intensive efforts are underway among the USGS, the Bureau of Reclamation, the Fish and Wildlife Service, the National Oceanic and Atmospheric Administration (NOAA), and the State of California to address what will be increasingly difficult decisions regarding allocations of water for human consumption and biological needs. The report's findings provide new information that can inform planning of next steps in collaborative initiatives —such as the Bay Delta Conservation Plan and contribute to the science foundation underlying the Delta Stewardship Council’s Delta Plan.
“As we plan for the future, it is important to consider more than just global warming,” said USGS scientist and the study's lead author James Cloern. “We also have to consider other drivers such as land-use changes and population growth. A comprehensive assessment of the future looks at responses to global warming in the context of all factors that will change the resources we value.”
In addition to providing future visions of the Bay-Delta system, this research provides general lessons to guide development of adaptation strategies for coping with climate change in other coastal landscapes. Anticipation, flexibility, and adaptability will be the keys to the success of those strategies.
Results of this study were recently published in the journal, PLoS ONE. The article, “Projected Evolution of California's San Francisco Bay-Delta-River System in a Century of Climate Change,” is available online.
Cheryl Kaften is an accomplished communicator who has written for consumer and corporate audiences. She has worked extensively for MasterCard (News - Alert) Worldwide, Philip Morris USA (Altria), and KPMG, and has consulted for Estee Lauder and the Philadelphia Inquirer Newspapers. To read more of her articles, please visit her columnist page.Edited by
Jennifer Russell
