Conditions in the Delta are changing at a rapid pace and the future is likely to look very different than the present as climate change, sea level rise, a growing population, earthquakes and major flooding, new invasive species, increasing water supply diversion demands, shifts in land use, and declines in native species will continue to affect the Delta and its ecosystem.  Decisions and policies made now could constrain options for the future in ways that can be imagined today, so if we are to meet these challenges successfully, it’s imperative to ensure that the scientific community provides insights for managing with change, as a lot of change lies ahead.

To date, the Delta’s overall science enterprise has developed science focused primarily on current management challenges, but are we on the right track?  What are the emerging issues? How do we build an effective forward-looking science enterprise for the Delta?  To address these questions, the Delta Science Program is convening a Science Needs Assessment Workshop in October of 2020 to explore rapid environmental change facing the Delta relative to climate and other change impacts and to develop a comprehensive science needs assessment that will contribute to a long-range science strategy.  The workshop will identify key science efforts that will provide answers and insights for likely management questions in the long-term; and discuss how to organize the science enterprise to address these complex and changing problems.

To prepare for the workshop, the Delta Science Program has organized a four-part discussion online discussion series to gather input to prepare for the workshop.

The first online discussion was held on April 28th, and featured Jay Lund and Steve Brandt from the Delta Independent Science Board and John Callaway, the Delta Lead Scientist, who provided background on the Delta ISB’s call for forward looking science with a focus on climate change, the purpose and need for the workshop, the advance briefing paper, and the current understanding of the changes and impacts of climate change on the Delta.


The science needs effort began with a letter from the Delta Independent Science Board (DISB) to the Delta Plan Interagency Implementation Committee (DPIIC) in February of 2019 that was written in response to the revision of the Delta Science Plan.

We thought the Delta Science Plan had a lot of good things in it, but we felt it wasn’t really taking account for the very rapid changes we’re seeing in the Delta and the need for science to really prepare for these rapid changes and get further out ahead of the policy discussions then where we are now,” said Dr. Jay Lund.  “So we wrote a letter to DPIIC from that experience and expressing a desire to see a more strategic science needs assessment, in addition to the Delta Science Plan and the science action plans, that are looking much further out into the future.”

Another offshoot from our letter in 2019 was a very interesting and very useful science board panel that had a series of presentations and discussions and a white paper on how the environment of the Delta is changing much faster than the traditional science can keep up,” Dr. Lund continued.  “I think that is producing some useful documentation and discussions and ideas that might help us out with this effort as well.”

Dr. Steve Brandt then discussed the background for the scientific needs assessment and in particular on the planned workshop.  For about the past eight months, a planning team has been discussing how to put together a robust scientific needs assessment in the context of changing environmental drivers and particularly a changing climate.  They have planned a two-day workshop to do the scientific needs assessment, and have developed two overarching goals and a series of four major topics to be considered.  At the workshop, each of the four topics will have a presentation, followed by a panel discussion and a breakout group.  The workshop is tentatively scheduled for October 5 and 6.

An advance briefing paper has been completed which discusses the overall rationale for doing a science needs assessment, the intended audience, and the various ways of doing a scientific needs assessment, as well as a draft agenda and outline for the workshop.  The paper includes a detailed list of questions for the four topics and appendices provide background on the current structure of the scientific enterprise, scientific funding in the Delta, connection of science to management, and other topics.

The overarching goals for the workshop are:

    • Identify key science efforts that will provide answers and insights for likely management questions in the long term;
    • Discuss how to organize the science enterprise to address these complex and changing problems.

The science needs assessment will feed directly into the Delta Science Plan as well as the Delta Science Action Agenda, which is scheduled to begin its update this year. 

The Science Action Agenda largely focuses on what science do managers need to know now, whereas the scientific needs assessment we’re talking about looks at what science do we need to start now to meet the challenges of managers in the near future,” said Dr. Steve Brandt.  “These two efforts are complementary, they will be going on in many respects simultaneously, and they are highly coordinated throughout.”

We expect that some of the science needs for the future will be more complex, they will be focused on perhaps require cross disciplinary integration as well as trying to be more predictive, so the question is are we ready, are we organized well enough to achieve those scientific goals,” he continued.

These are the four topics planned for the workshop and the focus of the online discussion series:

    1. What do we know about projected climate change impacts for the Delta?  What are we reasonably certain will happen in the future, what changes are likely particularly related to climate change and perhaps, what do we don’t know?
    2. What questions will that raise for management decisions? If we know the Delta is going to change in a certain way, what do managers need to know to effectively make decisions in that future Delta?
    3. If we know what the management needs are, what science needs to be done to give management the answers they need?
    4. Given that we expect the scientific needs will demand more complex cross-disciplinary efforts, probably requiring predictive tools and so forth, what changes are needed in our science governance, science funding, and integration in order to effectively meet the needs in the future?

The questions were designed to be progressive and are all intertwined with each other, said Dr. Brandt.  “It’s difficult to talk about science without talking about management almost in the same sentence.  Put simply, we’re really asking, what will happen in the future?  What does that mean to management?  How will science address those management needs in the future? And are we coordinated and integrated enough to do that science properly?

During the workshop, there will be breakout groups that will be topically oriented to make sure all main areas of interest in the Delta are covered, such as water supply, flood management, habitat management, native species, invasive species, water quality, land use, and Delta as an evolving place. 


The overarching question is, what do we know about these projected climate change impacts for the Delta?  Dr. John Callaway noted that the Delta and the entire estuary were created in large part by climate change and increased inundation from sea level rise.  The sequence of images on the slide from Brian Atwater’s work illustrates sea level rise over the past 15,000 years which has led to the migration of the coast inland and the creation of our unusual inland Delta at the confluence of the Sacramento and San Joaquin Rivers. 

Dr. Callaway noted that Michael Dettinger and his colleagues put together a paper from the State of Bay Delta Science titled, Climate change and the Delta, and the climate change synthesis put together for the Delta Plan’s ecosystem amendment; both of these are useful sources for more information on climate change impacts on the Delta.

Climate change is definitely a key part of the Delta system,” he said.  “These papers and others highlight that the key mechanisms for drivers for climate change impacts are increases in air and water temperature, changes in precipitation and runoff, and sea level rise.  And it is important to note that it’s not just gradual annual changes in these factors, but even more important, the extreme events and shifts in seasonal patterns that are likely to have major effects on the Delta.

There is no single time-frame that is ‘correct’ or best.  It could be relative short-term or anything out 100 years or more, Dr. Callaway said.  “It’s important to note that for the climate change issues, these will be more severe for the farther out we look, but the uncertainty in the magnitude of impacts will increase substantially over time.  So we definitely act now to prepare for the future, no single time scale is correct or best; rather, we just need to be aware of the various tradeoffs in terms of impacts, actions, and uncertainty.”

There are many other factors and changes that will be important to the overall conditions in the Delta, such as demographics, land use, human / social responses, invasive species, contaminants and nutrient inputs, and pandemics.


Changes in air temperature

The two figures on the slide show the historic and projected changes in air temperature in the Delta under two different IPCC scenarios.  The gray lines show the historic temperature changes, and the colors are the projected temperatures under two different climate change scenarios.

Things already are warming up, but they are likely to be much greater into the future with a five degree increase in Fahrenheit in the moderate scenario on the left and nine degrees increase with business as usual by 2100 on the right,” said Dr. Callaway.  “Water temperatures also will increase, and this likely will be one of the greatest stressors for aquatic species in the Delta.  And although obviously there will be year to year variability as is illustrated, the forecast for these changes are relatively certain.  In the timeframe of the next 20 or 30 years, there’s much more certainty than going out to 2100.”

Precipitation and runoff

For precipitation and runoff, the temperature shifts that are going to occur will lead to less snowmelt with more precipitation coming as rain.  That will occur even at higher elevations, so this will lead to earlier runoff in the watersheds and decreased Delta inflows in the summer and fall. 

These shifts are relatively certain given the linkage to temperature effects; however, shifts in overall precipitation are less certain with some models predicting increases and some predicting net decreases,” he said.  “In addition to these shifts, we’re likely to see an increase in extreme events.  So there will be increases in extreme events with more floods and droughts, and more extreme storm events and the atmospheric river events that we have are likely to become even more intense.

Sea level rise

Rates of sea level rise are already increasing globally which will lead to higher water levels and greater rates of inundation within the Delta.  As with temperature, these changes are going to accelerate with a range in forecasts and increasing uncertainty beyond the next two to three decades. 

In addition to increased water levels, sea level rise will also result in increased salinity in the Delta,” said Dr. Callaway.  “It’s important to note that subsidence is a key co-factor in addition to sea level rise in determining flooding risks across the Delta.  In large part because of this, the impacts of sea level rise will not be uniform throughout the Delta.  There is also likely to be substantial spatial variability in how the other factors such as the river inputs, are likely to affect the Delta.  This variability reflects much of what we understand about Delta dynamics – for example, that riverine inflows will not be uniform and much more important further upstream compared to sea level rise effects.”


Water quality impacts

Changes in sea level and shifts in runoff will lead to greater salinity intrusion within the Delta, especially seasonally when low flows are likely to be much less. 

If we think about this from a water management perspective, this means that greater freshwater flows will be needed to keep the salinity at bay and to maintain freshwater conditions at the water intakes,” said Dr. Callaway.  “In addition to the direct effect of increased temperatures, increasing temperatures will lead to lower levels of dissolved oxygen in the Delta waters, creating further stress for aquatic organisms.  Suspended sediment concentrations will be affected by changes in overall runoff in extreme events; this has implications for tidal wetlands as well as for aquatic species that are affected by turbidity.  And for water quality and all these impacts, it’s important to note that these will happen in conjunction with other factors – in this case, future changes in contaminants, nutrients, climate change related shifts in pH.”

Habitat and species impacts

In terms of impacts on species and the effects on their habitat, for aquatic organisms, the biggest effects are likely to be stresses related to increasing salinity and water temperature, while for wetland and floodplain species, increased inundation associated with sea level rise will be a major factor, along with increased salinity stress that will reduce plant productivity. 

Where possible, wetlands may migrate to higher elevations, and this is probably possible in Suisun Marsh and other areas with few opportunities for migration within the Delta.  Floodplain inundation may increase, although some models show that this will be more periodic due to increased storm intensity and won’t really create the sustained flooding that’s necessary to support native species.

There are many interacting factors to consider, such as invasive species, both current and new, that are likely to establish and many of them are more tolerant of higher temperatures so this may be more problematic for native species in the future.  And large scale restoration will increase overall habitat availability and improve habitat conditions going forward.

Human impacts

Dr. Callaway noted that the Council is currently undertaking a climate change vulnerability assessment for the Delta which includes evaluating impacts to both natural and human assets in the Delta with a focus on human related impacts.

Shifts in salinity and temperature will greatly affect water management efforts and water supply in the Delta,” said Dr. Callaway.  “Both sea level rise and increased storm-related river inputs will increase flooding risks for all land uses in the Delta.  In addition to flooding, changing temperatures will shift growing seasons with impacts on native species and on agriculture, and again there’s interactions with many other factors, from the potential for future conveyance infrastructure, to shifts in environmental regulations and other approaches to management.”


After the presentation, participants were given the opportunity to ask questions and give their comments.

Josh Collins suggested to identify Delta as both a bottom of great watersheds draining from the Western Divide as well as the regional top of the Pacific Ocean, as the Delta will continue to be transitory and subject to what happens downstream.

Mike Dettinger noted that most of the uncertainty that we have now is because we don’t know how society will change its greenhouse gas emissions, but by 2050, we will know more about the emissions and the big uncertainties looking forward will be less than they are now.   “Assuming our models are better, by then our uncertainties will decline even more, so big late century uncertainties are not written in stone when we are in the midst of those late century changes.  There’s hope that uncertainties will be smaller.  We will always have this range of uncertainties, so plans should be able to take advantage of the future, a few decades from now, when reductions in uncertainties may come.  Almost all the precipitation changes and runoff changes in long haul are now known to reflect changes in extremes, so those changing extremes are at the heart of nearly all those precipitation changes.  One form this will take is more of the water resource will have to come from floods.”

Kathleen Schaefer also noted about the need to consider effective environmental decision making and then Josh Collins noted, opportunities for estuarine transgression also known as migration due to sea level rise, will change as sea level rise affects property values. 

Dr. Callaway noted Mike Dettinger’s comments about how uncertainty is going to shift over time and be reduced as we get better insights on the long-term uncertainty.  “To me, that really points to that we should be thinking about the timeframe of 20 to 30 years out where there isn’t so much uncertainty and where we can do some management efforts that would have some significant effect, and then in 20 to 30 years, hopefully the longer term, the uncertainty around 2100 will be reduced and give us better insight into where we might go forward.”

Similarly, Josh with the transgression issues highlights that things will change and it’s an interaction of both climate change as well as economic issues and property values that will create opportunities for migration, so I think it really pushes what we’ve been trying to do at the council which is think more about interactions between physical factors and social factors and how we can improve our understanding and decision making, incorporating those different sources of information.”

Deirdre Des Jardins asked about needed hydrodynamic modeling for sea level rise in the Delta.  Dr. Jay Lund agreed that more is needed, as well as public discussion and insights based on the modeling results.  He acknowledged there are some efforts in the works, but they’ve been in the works for a long time and have yet to be finished.

Amanda Bohl noted that one of the responses to the poll conducted earlier in the webinar was to consider these questions beyond the Delta and Suisun Marsh and take a more watershed-wide view on all of this.  While she completely agrees, she noted that one issue identified through the workshop planning process and science funding and governance initiative process that preceded it was that at this point, they should focus on is known and what can be managed at the moment.  However, in white papers that have been drafted, they have noted that in the long-term, they need to figure out a way to be addressing these issues from more of a watershed perspective.

Josh Collins commented to consider the possibility that the margins of the estuary may be more dynamic and naturalistic or simply wild in the future then they have been in the last 200 years.  What does this mean for native wildlife conservation and our future biogeography?

Certainly as you’re changing these environmental conditions, particularly temperature, you change the habitat features in such a way that it will open the door to new invaders and close the doors to those that are living on the margins as well,” said Dr. Steve Brandt.  “Clearly that’s one of the questions we would hope that managers would begin to raise on this and then talk about what kind of science we need to address those.”


The second science needs assessment virtual discussion series will be on Wednesday, June 3 at 9:15am.  The session will begin with a panel discussion among Paul Souza (US Fish and Wildlife Service), Jennifer Pierre (State Water Contractors), and Campbell Ingram (Sacramento-San Joaquin Delta Conservancy) on what decision-makers and stakeholders need to know in the future, as well as the implications of future changes on management needs.

Instructions for joining the webinar:

  • Join via MS Teams
  • If you do not have a Microsoft or Office 365 account, please click “Join on the Web instead”
  • You will be able to use the microphone on your computer. If you have a computer camera, please only turn it on when asking questions or providing comment
  • If you do not have access to a microphone on your computer or have issues logging in, please dial the following number on your phone: +1 916-432-5700 (Conference ID: 308 969 830#)


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