Projected Evolution of California's San Francisco Bay-Delta-River System in a Century of Climate Change

Abstract

BackgroundAccumulating evidence shows that the planet is warming as a response to human emissions of greenhouse gases. Strategies of adaptation to climate change will require quantitative projections of how altered regional patterns of temperature, precipitation and sea level could cascade to provoke local impacts such as modified water supplies, increasing risks of coastal flooding, and growing challenges to sustainability of native species.Methodology/Principal FindingsWe linked a series of models to investigate responses of California's San Francisco Estuary-Watershed (SFEW) system to two contrasting scenarios of climate change. Model outputs for scenarios of fast and moderate warming are presented as 2010–2099 projections of nine indicators of changing climate, hydrology and habitat quality. Trends of these indicators measure rates of: increasing air and water temperatures, salinity and sea level; decreasing precipitation, runoff, snowmelt contribution to runoff, and suspended sediment concentrations; and increasing frequency of extreme environmental conditions such as water temperatures and sea level beyond the ranges of historical observations.Conclusions/SignificanceMost of these environmental indicators change substantially over the 21st century, and many would present challenges to natural and managed systems. Adaptations to these changes will require flexible planning to cope with growing risks to humans and the challenges of meeting demands for fresh water and sustaining native biota. Programs of ecosystem rehabilitation and biodiversity conservation in coastal landscapes will be most likely to meet their objectives if they are designed from considerations that include: (1) an integrated perspective that river-estuary systems are influenced by effects of climate change operating on both watersheds and oceans; (2) varying sensitivity among environmental indicators to the uncertainty of future climates; (3) inevitability of biological community changes as responses to cumulative effects of climate change and other drivers of habitat transformations; and (4) anticipation and adaptation to the growing probability of ecosystem regime shifts.

Science Advancements Key to Increasing Management Value of Life Stage Monitoring Networks for Endangered Sacramento River Winter-Run Chinook Salmon in California

“…• Generate robust estimates of juvenile SRWRC abundance at key locations system-wide, and allow survival among years and environmental covariates to be evaluated to identify key factors that influence juvenile production (Cloern et al 2011). …”

“…This life history diversity results in adult salmon and juveniles occupying the Central Valley year-round. Current and pre-historic climate variation also presents physiological constraints, which contribute to the existing patterns of habitat use (Cloern et al 2011).…”

Effects of nutritional deprivation on juvenile green sturgeon growth and thermal tolerance

“…60 % of the natural freshwater inflow , which has resulted in increasing summer water temperatures ) and upstream salinities (Cloern and Jassby 2012). Climate change is projected to further increase temperatures of the SFE and the Sacramento River at a rate of 0.1 to 0.3°C per decade, depending on the location and climate model applied (Cloern et al 2011). Intolerably high water temperatures during the late summer, coupled with low nutritional energy supply, may threaten young sturgeon before they develop the osmoregulatory capacity to access cooler seawater.…”

Recent Advances in Understanding Flow Dynamics and Transport of Water-Quality Constituents in the Sacramento–San Joaquin River Delta

“…Both the salinity field and tidal motions are the result of interaction of the Bay-Delta with physical forcing that itself varies in time. Outflow of freshwater from the Delta, the key factor that suppresses upstream propagation of salt, will likely change in the future because of changes in precipitation patterns caused by anthropogenic climate change (Cloern et al 2011). At the same time, SLR is expected to have two effects: (1) gravitational circulation will be stronger when channel depths are larger, increasing upstream dispersive salt fluxes so the outflow required to maintain a particular value of X2 will be larger than it is now (Chua and Xu 2014); and (2) because of the likely flooding of large flat areas adjacent to the current Bay-Delta, frictional damping of tides will be stronger, and so tidal propagation through the system will likely change (Holleman and Stacey 2014).…”

“…Delta water temperatures are strongly related to air temperature, and not as much to Delta inflow rates ), so increased air temperatures will warm Delta waters. For scenarios of curtailed and increasing greenhouse gas emissions, Cloern et al (2011) andWagner et al (2011) estimate there will be statistically significant increases in Sacramento River and Delta water temperatures. Delta water temperatures will increases up to 5° C in summer, a change that may prove lethal for Delta Smelt.…”