DELTA ADAPTS: Climate change vulnerability assessment looks at climate impacts to Delta as a place, agriculture, recreation, and infrastructure

Delta Adapts: Creating a Climate Resilient Future is the Delta Stewardship Council’s effort to conduct the first-ever climate change vulnerability assessment and adaptation strategy for the Delta and Suisun Marsh. At the November 2020 Council meeting, Council staff presented selected key findings from the draft vulnerability assessment.  At the December Council meeting, Assistant Planning Director Harriett Ross presented additional initial findings from phase one of the Delta Adapts climate vulnerability assessment, including the economics analysis and the impacts to the Delta’s people, places, agriculture, recreation, and infrastructure.

Economic analysis

The economics analysis considers how flooding under climate change is projected to expose assets and economic activity to risk within the Delta. It also considers how climate change is estimated to impact water supply and how those changes might influence economic activity from the State Water Project and the Central Valley Project.

The analysis covered a range of flooding and water supply scenarios. The analysis does assume asset values and economic activity from 2018 and is based on existing land use.   Ms. Ross pointed out that it’s an exposure analysis and not a damage assessment, so the asset values are based on total replacement costs, while the economic activity is generally based on loss of operations for one year only.  For the water supply piece of that analysis, which was presented last month, those impacts are generally expressed in lost annual economic activity and those corresponding values experienced by local water districts and agricultural uses.

Last month, staff presented a series of flood risk maps at different planning horizons, along with some numbers on population and the amount of land that could be flooded. They now have additional data that includes the economic value of those exposed assets.

Ms. Ross briefly gave an overview and explained the process of how the analysis was done.  For current conditions, about 2% of the Delta’s population, less than 10,000 people are exposed to 100-year storm event at this point, or 1% chance of flooding every single year; approximately 3000 of those residents are located in highly socially vulnerable areas.  The area exposed to flooding equates to about 10% of the Delta’s land, including 43,000 acres of agriculture totaling about a billion dollars in exposed assets.

Under 2050 conditions, more flooding is expected and these numbers increase.  About 10% of the Delta’s population would be exposed to flooding with almost 43,000 residents in socially vulnerable areas.  The flooded areas in the Delta are about a third of the land with over 148,000 acres of agriculture exposed close to $10 billion in exposed assets. 

In 2085, all of these numbers increase with more expected flooding; two-thirds of the Delta’s population would be flooded in a 100-year event, exposing 21% of the population and over two-thirds of the land, including over 250 1000 acres of agriculture, which totals about $19.6 billion in exposed assets in the Delta.

For relative comparison, Ms. Ross noted that a similar study of the economic costs of sea level rise in the Bay Area estimated that it would cost about $70 billion to replace all the structures in the Bay Area under a similar 2085 flood scenario.  However, she did acknowledge the two figures aren’t directly comparable because the Bay Area is more urban with higher property values.

The vulnerability assessment considers impacts at both 2050 and 2085. The key findings are based on the flood map (right), which is shown for 2050.  Assets are considered flooded when they’re located in a 100-year floodplain or in an area with a higher chance of flooding, which is shown by the three darkest blue colors in the legend.

These are areas flooded from levee overtopping only and assumes the Delta levees remain in their current conditions.  The flooded areas are concentrated in the central and southern Delta as well as Suisun Marsh.

Impacts to people

In addition to flooding, the vulnerability assessment also looks at impacts from extreme heat and wildfire smoke for people and communities, this asset. And so based on the flooding scenario shown in the previous slide, there are roughly 66,000 people in the Delta who would have a 1% chance of experiencing flooding each year by mid-century.  Two-thirds of those exposed populations live in communities with high social vulnerability, which are defined as communities with limited resources to prepare for or recover from flooding.

With regard to extreme heat exposure, state climate models were used to project extreme heat days at mid-century and end-of-century conditions. The Delta region currently experiences less than 10 extreme heat days per year; the models project that will increase to about 17 to 25 days per year, depending on the location in the Delta. All communities will experience a significant increase in extreme heat days.

However, Ms. Ross noted that the people in the cities of Tracy and Stockton have particularly high vulnerability because they have communities with a high social vulnerability that will experience the greatest change in exposure.  Those cities specifically are projected to experience approximately 25 extreme heat days per year compared to the current five days per year.

Based on the literature review and qualitative analysis of vulnerability to wildfire, which is also expected to increase, it was concluded that the greatest potential wildfire hazard is the air quality impacts.  The air quality impacts due to the wildfire smoke combined with the increase in extreme heat days pose a risk to people’s health in communities throughout the Delta.

Impacts to Delta as a place assets

There are a variety of assets for Delta as a place, including cultural sites, critical facilities, and residential and commercial buildings. Using the same flood map to overlay on the assets, it was determined that in 2050, six culturally significant sites would be exposed to flooding, which could damage or destroy these areas that have played a significant role in the Delta’s history.  Specifically, there are four historic sites, three of which are located in San Joaquin County and one in Isleton. And two legacy towns would be exposed: Rio Vista and Isleton.

By 2050, 11 fire stations, 19 schools, 11 wastewater treatment plants, and nearly 17,000 parcels of residential uses and over 2000 parcels of commercial and industrial uses would be exposed to flooding. And both of those combined values are close to $4 billion.  Lastly, more extreme heat events will put more demand on these critical facilities due to heat-related injuries and illnesses and will also result in more energy costs to cool homes and buildings.

Impacts to agriculture

Changing climate conditions, including increasing warming temperatures and extreme precipitation events, will continue to increase and likely affect Delta agriculture.  Flooding exposure is estimated to impact approximately 148,000 acres, or about 35% of the land currently being farmed now, which amounts to about $72 million in assets and an additional $79 million in annual economic activity would be interrupted were flooding to occur. Ms. Ross reminded that the analysis assumes only one year of disruption.  Much of the agricultural areas exposed to flooding are located in San Joaquin and Sacramento counties.

Some crops will benefit from a longer growing season, but overall crop yields are expected to decrease with increased stress from variable temperatures and water quality. Summers will be longer and hotter, with more days of extreme heat.  There will be less tule fog and winter chill, both of which are vital for fruit and nut tree yields.   Impacts from droughts and sea level rise together may increase episodic negative impacts on water quality and present soil salinity management issues for farmers.  Many of these Delta crops are sensitive to changes in salinity, temperature, and water schedules, which could affect plant and overall crop yields.

However, Ms. Ross noted there are some positives.  Warmer temperatures will likely increase yields for some of the Delta crops while negatively affecting others.  Accelerated growth may positively influence some crop yields, but it could negatively impact overall crop quality.

We have a whole technical memorandum that’s based on a literature review which has been reviewed by some of our stakeholders in our technical advisory committee,” she said.  “There’s a lot in the memo and those are the basic findings.”

Impacts to recreation

There’s a wide variety of recreational opportunities in the Delta, but Ms. Ross noted that some of those are limited and not all publicly accessible. The recreation asset type looks at parks, campgrounds, marinas, scenic highways, trails, and similar assets.  Recreation assets are important because they provide access to unique wetland and open water areas, and they increase the Delta’s appeal as a place to live and visit.

The flooding analysis shows exposure of approximately 45 parks and campgrounds, which is significant because the Delta is really short on areas accessible to the public and amenities overall.  Specifically, 13 campgrounds would be exposed to flooding, representing more than one-quarter of the campgrounds total in the Delta.  Most of these campgrounds and parks are located in or near the cities of Stockton and Lathrop, and most of the trails and scenic highways affected are in Sacramento County. Anticipated extreme heat events also may negatively impact visitation to recreational facilities in the future. And lastly, drought conditions and changing precipitation may impact specific activities such as fishing and boating in the future.

Impacts to infrastructure

Impacts from flooding and extreme heat to energy facilities, utilities, transportation, solid waste facilities, flood management infrastructure, and water supply infrastructure were considered.  A range of natural gas and oil pipelines and wells could be exposed to flooding with an estimated value of about $800 million, while the value of electrical facilities exposed total about $1.5 billion and includes substations, transmission towers, and transmission lines.

The Delta is home to regional transportation routes that would disrupt jobs and businesses that rely on them if exposed to floods. Flood exposure to roads are valued at about $1.1 billion, and railroad facilities are valued at about 83 million.  Some of these facilities also serve as evacuation routes.

Flooding is also anticipated to affect the Port of Stockton, which is the state’s fourth busiest port, and impacts may result in job losses and impacts other impact other businesses that rely on the port daily. There are also solid waste facilities, contaminated sites, and hazardous waste facilities that can be exposed to flooding, which would increase the risk to health and safety to Delta residents and ecosystems with the potential release of trash and toxic materials during flood events.

Approximately 1300 miles of levees can be exposed to flooding, putting stress on the entire system.  Nearly 50 miles of water conveyance infrastructure and a number of state and local points of diversion, as well as over 3400 private points of diversion such as pumps, could be impacted by flooding that will have major consequences for the users that rely on water in the Delta.  Then extreme heat can also reduce the ability to transmit power, making power outages more common and can damage roadway and real infrastructure.

Stakeholder workgroup meeting

Next, Ms. Ross briefly discussed the recent stakeholder workgroup meeting which was attended by about 50 participants representing various Delta interests.  An overall presentation was provided to orient the stakeholders to the vulnerability assessment structure, and then went through the findings so they would know where to focus their attention during the public review period.  They then broke into small groups to discuss the findings and to answer questions in the small group setting.

Overall, the feedback we got no one was really surprised by the findings that they heard just really more questions on our approach,” Ms. Ross said.   “There were a couple of comments that I wanted to share. One was that they really want us to focus on solutions, which is what we’re going to be looking at the adaptation phase of the project.   We also heard from others that our study will be useful for communities to utilize and as an advocate for themselves, given now that they understand the climate vulnerabilities that they face.”

Staff is planning on releasing a public draft vulnerability assessment in January for a 30 day public comment period.  They will then make any necessary revisions and present a final vulnerability assessment to the Council.  They will then begin developing the adaptation strategy.

Discussion highlights

Chair Susan Tatayon asked with respect to developing the adaptation strategy, has the current TAC or stakeholders who have engaged have they offered any concepts or ideas or cautions?

Not really in any formal capacities, but we’re definitely starting to get more and more comments, such as, ‘Thank you for the vulnerability assessment. What are we going to do about it?‘” said Ms. Ross.  “I have heard others say the Council should take on a big role in adaptation as stewards of the Delta, but we haven’t had any formal discussions yet. We are beginning that research and due diligence phase as we put out the vulnerability assessment for public comment, considering what models, successful or even unsuccessful models, can we look to for understanding how to best develop and discuss and eventually fund adaptation strategies?

Chair Tatayon said what would be helpful when thinking about adaptation strategies is the timing of these potential impacts.  “When do we need to be prepared to do what? For example, if I know that 100-year flood is likely to occur much more often in these locations and having these effects, I could think more clearly about, is this is just a matter of just flood proofing buildings or matter of massively altering the transportation system for evacuation routes.  The maps are so helpful in this, but I don’t have a good handle on timing and magnitude of impact. And how would one prepare? If I develop an array of adaptation strategies, how long will it take to implement those strategies?

Our maps talk about the probability; the exact timing obviously is not known,” said Ms. Ross.  “The trends are accelerating and things are happening much more quickly. But we can tie it to a timeframe on; we can certainly get that information together for our next discussion on adaptation.” 

Oscar Villegas suggested to include a list of all the stakeholders and organizations who provided comments be included in an appendix.  “It’s almost simple as identifying who got notified, who responded, and who didn’t,” he said.  “I’ve seen other documents that have done that, and I think it’s very effective to be able to look at the laundry list of organizations that were sent the document and provided no comment.  They offered no valuable feedback, but they complained immediately after the report was produced. And so I think that’s an important sort of demarcation.”

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