More frequent floods
Extreme high Bay water levels will occur more often, leading to more frequent flooding in flood-prone areas that could cause disruptions of emergency services and access to power, water, food, and medical care.
More extensive, longer-duration
Higher Bay water levels especially during storm events will flood larger areas for longer periods of time. Along with many other potential impacts this may result in the increased mobilization of pollutants if contaminated lands such as closed landfills are subjected to prolonged inundation.
Sea level rise will cause areas not currently exposed to the tide to be inundated, resulting in the need to either protect or move people and infrastructure, and the loss of trails, beaches, vistas, and other shoreline recreation areas.
Shoreline erosion and overtopping
Higher Bay water levels will cause changes in tidal and wave energy, leading to increased shoreline erosion and the potential that levees and other types of shoreline protection will be overtopped.
Elevated groundwater and increased salinity intrusion
As the Bay rises, groundwater levels and salinity intrusion will increase, affecting water supplies along the shoreline, damaging below- or at-grade infrastructure, requiring additional pumping and costly maintenance and repairs of stormwater and flood control facilities, and increasing the risk of earthquake induced liquefaction.
To learn more about these impacts, download the Climate Impacts Statements () from the ART Subregional Project, and click on the “Climate Impacts Gallery” below to see animations of each of the five climate impacts.
Six future climate scenarios were selected to support the vulnerability and risk assessment (). The six future climate scenarios were based on two sea level rise projections and three Bay water levels. The two sea level rise projections, 16 inches (40 cm) and 55 inches (140 cm), correlate approximately to mid- and end-of-century time frames. These projections were consistent with the October 2010 State of California Sea Level Rise Interim Guidance, which was based on best available science at the time of publication. They are also within the ranges reported in a more recent study conducted by National Academy of Science ().
The Bay water levels selected correspond to three tide and storm conditions:
- The highest average daily high tide represented by mean higher high water (MHHW)
- The 100-year extreme tide level, also known as the 100-year stillwater elevation (100-year SWEL)
- The 100-year extreme tide level coupled with wind-driven waves
Extreme tides are the maximum high tide level that has occurred over a specific return period that correlates to a probability of occurring. For example, a 100-year tide has a return period of 100 years and therefore a 1% chance of occurring in any given year.
Daily High Tides vs. Extreme Tide Levels
The daily high tide (MHHW) was selected to inform which shoreline areas not currently exposed to tidal action could be exposed to the high tide with sea level rise. This Bay water level is important because exposure to the daily high tide would result in frequent or permanent inundation, potentially leading to the slow yet chronic degradation of asset physical condition or function.
In contrast, assets exposed to a 100-year extreme tide level would be subjected to infrequent and temporary, but potentially severe, flooding. Extreme storms can cause overtopping and erosion of shoreline protection assets, exposing large inland areas to fairly deep flood depths and high velocity flows. Wind waves can elevate water levels significantly above stillwater levels, potentially increasing the severity of flooding. It is critical, therefore, to consider the effect wind driven waves could have on inland inundation during a coastal storm event.
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- Eliza Berry