DELTA COUNCIL: Addressing climate vulnerabilities in the Delta

At the July meeting of the Delta Stewardship Council, Associate Deputy Executive Officer Harriet Lai Ross updated the Council members on the Delta Adapts project.

Delta Adapts is a two-phase initiative.  The first phase was the vulnerability assessment, completed two years ago.  The vulnerability assessment identified the people, assets, and resources most vulnerable to increased climate impacts related to flooding, droughts, and wildfire smoke.  The second phase, the adaptation plan, will outline the strategies to respond to those vulnerabilities.

The development process began with extensive stakeholder outreach, which included focus group meetings and discussions with planning partners, farmers, and landowners in the Delta.  The information collected was used to develop a set of scenarios and metrics; they then evaluated the metrics for each scenario to determine trade-offs.   The scenarios and metric evaluation were presented at the June stakeholder workgroup meeting.

Staff is currently working on identifying adaptation strategies and implementing actions.  Strategies can be physical (such as levee investments) or management (such as prioritizing flood improvements for socially vulnerable communities first).  Staff plans on releasing a public draft of that adaptation plan by the end of the year, with the plan being finalized early next year.

The Delta’s key climate vulnerabilities are:

  • Equity – not all communities will be impacted by climate change the same; underserved communities will bear a disproportionate share of these impacts.
  • Ecosystems – the historical extent of the ecosystems has declined by as much as 95%.
  • Flood risk – about three-quarters of the current ecosystems behind levees are projected to be exposed to flood risk by the end of the century, and 100% of tidal wetlands will be exposed. By 2050, substantial flooding throughout the Central and South Delta is projected to occur.  “The numbers indicate about 35% of the Delta’s land area, and over 10% of the population will be exposed to 100-year flood by 2050,” said Ms. Lai Ross.  “Of that population exposed, 65% are people living in communities considered highly socially vulnerable.”
  • Agriculture – about 148,000 acres are vulnerable, which equates to about $73 million in flood exposure of agricultural assets. About 79 million estimated annual agricultural economic activity could be affected.
  • Water supply reliability – the more variable precipitation expected leads to more extreme wet and dry years with fewer normal years. Delta exports could decrease by about 10% on average and 20% in drier years.

While these climate vulnerabilities exist statewide, the Delta has unique characteristics that distinguish it from other parts of the state.  The Delta is the heart of the state’s water supply; two-thirds of Californians receive a portion of their water from the Delta.  It’s ecologically important; hundreds of unique species live there.  Agriculture is the primary economic driver.  The Delta’s current flood risk will only increase with continued climate change.  There are challenges with subsidence due to the peat soils.  Many socially vulnerable populations may be exposed to flooding and extreme heat.


Scenarios are different ways to adapt on the landscape to maximize adaptation needs.  Models were used to guide and inform physical strategies, although many of the strategies are not tied to any of the scenarios.  Ms. Lai Ross noted that the scenarios were not intended to be a parcel-level plan for adaptation, and a land use map will not be included with the adaptation plan.

Four adaptation scenarios were analyzed:

Scenario one is a climate-smart agriculture scenario that focuses on continuing existing land uses, which, in the Delta, is primarily agriculture.

The biggest benefit of scenario one is that it maintains agricultural jobs and revenue and maximizes the protection of prime farmland compared to the other scenarios.  However, there are continued high greenhouse gas emissions.

Scenario two focuses on meeting restoration targets and the habitat types identified in the Delta Plan.  This scenario assumes that restoration occurs on suitable public lands first.

For scenario two, the biggest benefit is that it meets the overall targets of the Delta Plan for restoration and by habitat type, and there are corresponding benefits to restoration, such as less greenhouse gas emissions.  However, there are fewer agricultural jobs and reduced agricultural revenue in the Delta.

Scenario three focuses on meeting the overall restoration goal of 60 to 80,000 acres but minimizes the conversion of prime farmland.

Overall restoration targets are met, but less than with scenario two.  Prime farmland is reduced by about 15,000 acres.


Scenario four assumes less funding for flood risk reduction is available, highlighting the trade-offs that would occur with less investment in levee improvements.

These include impacting socially vulnerable communities and flooding portions of a state highway and a wastewater treatment plant.

Working with the focus group members, a set of metrics was defined.  They then ran the models and evaluated the trade-offs related to ecosystem, agriculture, flood risk reduction, water quality, economics, and equity among the scenarios.  For example, they looked at changes to agricultural jobs and revenue under each scenario, how different amounts of subsidence reversal would affect greenhouse gas emissions, and the levee improvement costs necessary to support each scenario.  A dashboard has been created to visualize the data and the results; the dashboard is available here.

Scenario insights

Ms. Lai Ross reiterated that they won’t be including an adaptation land use map in the final report.  The scenarios were more about evaluating different types of land uses and how to maximize different adaptation needs.

“We learned a lot from that effort,” she said.  “We learned what stakeholders value, what they want to see in adaptation, and what benefits and trade-offs are associated with each scenario.  We found that levees are a cost-effective adaptation.  We learned that public lands alone cannot meet our restoration goals and that large-scale restoration as called for in the Delta Plan will not negatively impact salinity in socially vulnerable communities.”

The scenarios and the metric evaluation were presented to the stakeholder workgroup meeting, and through those discussions, the stakeholders emphasized the importance of flood protection and levees.  “The cost of levee maintenance is often underestimated, and stakeholders think the state should play a greater role in funding levee maintenance given its importance.  Subsidence is a major problem, making it difficult to maintain water supply reliability and levee integrity.  And there were many ways suggested to address subsidence.”

Another key takeaway is funding mechanisms for adaptation projects must be identified and secured.   Stakeholders noted the need to align incentives from federal and state objectives and to provide incentives for carbon sequestration and restoration.  There is a recognition that trade-offs will be required.  There was agreement that the protection of vulnerable communities should be prioritized.  Stakeholders also recognized that traditional approaches to managing the Delta are no longer enough; new ideas and solutions are needed.

Next steps

Ms. Lai Ross said that they have sent out a letter requesting tribal consultation, and they are working on drafting the adaptation strategies and implementing actions this summer.

“We’ll be working with the focus groups, environmental justice expert group, and the stakeholder work group in the fall to really make sure we have the strategies right,” said Ms. Lai Ross.  “The hope is that we’ll be able to release a public review draft by the end of this year.”

But is it realistic … ?

During the public comment period, Gilbert Cosio with River Delta Consulting expressed his skepticism that significant land will be available for habitat restoration.  Crops are changing in the Delta; many farmers have put in permanent crops, such as grapevines, walnuts, and blueberries.

“If you look at the maps for scenarios two and three, especially Grand Island, Ryer Island, Pearson district up in Courtland, there are a lot of permanent crops, and yet they’re slated because they’re deeply subsided.  Those farmers making money on grapes aren’t going to pull up 20,000 bucks an acre investment and plant rice. … So there’s very little ground really available … I don’t know if the staff has actually looked at the Delta Plan’s goals.  Are those goals realistic?  Can we come up with so many 1000s of acres?  I don’t know. … I don’t think you can.  Farmers are doing everything they can to keep farming … especially these multi-generational farmers, they’re not going to leave until somebody pulls them away, or an earthen levee fails, and they can’t come back.”

“Habitat doesn’t pay the bills.  And these levees cost a lot of money, drainage costs a lot of money, and even with habitat, you can have a lot of drainage costs … The plans are in good shape right now for a high level.  But I think the staff needs to start getting closer to the ground … We do have to start breaking this down to the ground level and try to figure out, is this going to be doable or not?”

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