SCIENCE SPOTLIGHT: Australian wildfires and California drought

At the June meeting of the Delta Stewardship Council, Delta Lead Scientist Dr. Laurel Larsen spotlighted an article on the connection between the Australian wildfires in 2020 and California’s recent drought.

Recent headlines have been proclaiming the return of El Nino and what this means for expected weather patterns varies across the country and the world.  For California, it generally means likely wetter than average conditions are expected; the opposite are the La Nina years, which have typically been associated with drought in California, as the atmospheric rivers carried by the jet stream generally are diverted north of California under those conditions.

El Nino and La Nina refer to different temperature patterns in the Pacific Ocean associated with very different patterns of atmospheric circulation.  Typically, the La Nina conditions that bring California drought follow El Nino years.  However, this was not the case in the 2020-22 drought, when a strong La Nina developed on the heels of a normal water year.  Consequently, models did not foresee the onset or the severity of the drought or the development of La Nina conditions in 2020.  In fact, NOAA had issued a forecast for neutral conditions (meaning not either El Nino or La Nina) as late as June 2020.

So the question is, can global climate models be improved to better predict upcoming La Nina or El Nino conditions?  Dr. Larsen said this is an applied science question that lies at the heart of much of the research directed toward understanding these large-scale atmospheric and oceanic phenomena.  This month’s spotlighted paper, A multiyear tropical Pacific cooling response to recent Australian wildfires in CESM2, which appeared in the journal Science Advances, tested a hypothesis that the 2019 Australian wildfires may have had something to do with the La Nina conditions associated with the severe drought in California.

“It was a good guess with a sound foundation,” she said.  “Scientists do know that volcanoes that spew a lot of particulate matter high in the atmosphere can trigger ocean cooling in key locations and cause the onset of La Nina conditions.  So it makes sense to speculate that major wildfire seasons can do the same.  And the summer of 2019 to 2020 in Australia was a banner season for wildfires that came to be known as Black Summer.  That year, 94,000 square miles burned, causing an estimated $78 to 88 billion Australian dollars in damage.  Thirty-four people were killed, and over 3000 buildings were destroyed, most of which were homes.”

To test their hypothesis, the research team put aerosolized particles matching the wildfire emissions measured by satellite into global climate models and ran the model ensembles, each consisting of 30 different versions of the climate models, with and without those particles.  Improvements had been made to the model ensemble to more accurately simulate the aerosol dynamics, their three-dimensional nature, and how fire emissions move through the atmosphere.

“Sure enough, in their findings, the models with the particles that matched those observed from the wildfires produced ocean cooling in the equatorial South Pacific, setting off the sequence of events associated with the development of La Nina conditions in 2020,” said Dr. Larsen.  “And what’s more, and this was actually kind of surprising to the researchers, the effect persisted for several years, which provides a sufficient probable cause for the large-scale atmospheric circulation patterns that triggered the 2020 to 2022 California drought.”

Dr. Larsen noted that for the sake of completeness, the record-high temperatures that California experienced during those years deepened the severity of drought by increasing evapotranspiration and drying out soils and ensuring that more of the precipitation the state did receive fell as rain rather than snow.

“One of the most important takeaways from this spotlighted study is that climate models should incorporate global feedback processes related to wildfire.  In other words, warming temperatures dry out vegetation to a great extent contributing to greater wildfire occurrence; wildfires emit particulate aerosols, which may trigger localized ocean cooling with impacts to these large-scale atmospheric, oceanic circulation patterns that can trigger or exacerbate drought in certain locations like California.”

“So in the meantime, it’s important for California water managers to be aware of these potential what scientists refer to as teleconnections when we see wildfires developing in certain parts of the world,” Dr. Larsen said.  “I hope this research team undertakes a similar study prospectively with the Canadian wildfires that we’re seeing right now, but it’s likely that those would have pretty different impacts, given that the northern hemisphere has much less ocean than the southern hemisphere.”


Decision-making under deep uncertainty webinar series

The Delta Independent Science Board has been convening a series of seminars focused on decision-making under deep uncertainty.  It is separate from the Delta ISB’s thematic review of the topic but will inform the review.  The second seminar in the series took place on June 14, featuring Robert Lempert, a principal researcher at the RAND Corporation, and Andrew Schwarz, the State Water Project Climate Action Coordinator for the Department of Water Resources.

“Dr. Lempert spoke about tools that are available for conducting decision-making under deep uncertainty, and one of the things that really stood out for me in his presentation was the focus on how equity can have different possible solutions, which is often one of the big uncertainties can be accounted for in the decision-making process,” said Dr. Larsen.  “So that’s quite relevant to a lot of what we’re considering in the council.  And then Andrew Schwarz talked about how some of these specific tools are being applied in California by the Department of Water Resources and how there is a growing shift towards not just planning for the mean or the median of what the climate models forecast but also considering the extremes.”

Independent Scientific Peer Reviews and Advice

The reviews that the Delta Science Program convenes are different from those conducted by the Delta Independent Science Board.  Other agencies request the Delta Science Program to conduct the review, and they focus on specific scientific and technical programs, plans, and products rather than broad themes or programmatic areas.

The reviews involve external independent subject matter experts ultimately selected by the Delta Lead Scientist and include a charge to the review panel developed in consultation with the requesting entity but finalized by the Delta Lead Scientist.  Reviews can be conducted through individual letters or a panel review conducted in a public meeting.  A page on the Council website features all the review materials and bios for the panel members selected for each review.

“The peer review panels that we facilitate follow rigorous and consistent standards to ensure the independence of the review process,” said Dr. Larsen.  “And all of our best practices and policies are specified in Appendix I of the Delta science plan.”

The Delta Science Program is currently facilitating three reviews, one for the Department of Water Resources and two for the Bureau of Reclamation.

State Water Project Delivery Capability Report, or DCR

The report provides essential information about the current and projected future water supply reliability from the State Water Project for 20 years in advance.  The report is issued every two years and is used extensively by State Water Project contractors and others to plan their water uses.

DWR has requested a review of recent updates to the Delivery Capability Report development process that focus on improvements on how climate change impacts are estimated, including the incorporation of some of the new tools for decision-making under deep uncertainty.

The review is being conducted in two parts:  The first will evaluate the strategy for adjusting how the model uses historical hydrologic data to account for changes in non-stationarity due to climate change.  The second part will focus on the use of risk-informed climate change scenarios that use decision-making under deep uncertainty tools to model future deliveries.  The review work has just started;  review letters from three independent reviewers are expected to be available in the fall of 2023.

Review of the Bureau of Reclamation’s water temperature moderate modeling platform

Temperature management has long been a key parameter for protecting salmon and other species that require cold water at certain times of the year.  It is only growing in importance with climate change as water and air temperatures warm consistently.  Water temperature management is one of the most challenging goals associated with reservoir operations for Reclamation’s Central Valley Project.  So to help with water temperature management and to help with reservoir operations, Reclamation has developed a water temperature modeling platform, which comprises a set of modeling tools to assist resource managers of the major dams with balancing water resources for downstream uses and temperature needs.

A five-person independent peer review panel was convened last year to review the water temperature modeling platform and its application to a subset of tributaries within the Central Valley Project.  The panel met in July of 2022 and produced a report with recommendations for Reclamation last September.  Now Reclamation has integrated those recommendations into the latest version of the water temperature modeling platform, and a final review by that same panel will occur at a public meeting in September 2023.  The final report is due in October 2023.  It will cover the application of the water temperature modeling platform to a different set of tributaries within the Central Valley Project system than those previously reviewed.

Review of the fish and aquatic effects analysis for the long-term operations of the Central Valley Project

The long-term operations of the Central Valley Project and the State Water Project require compliance with the Endangered Species Act to avoid putting endangered species in jeopardy of extinction through the operation of the dams and reservoirs.  Under Section 7 of the Endangered Species Act, changes to the long-term operations require consultation with the US Fish and Wildlife Service and the National Marine Fisheries Service if those changes might cause effects on listed species or critical habitats not analyzed in the current biological opinions.

So as part of the reinitiation of consultation currently underway, Reclamation is now developing fish and aquatic effects analysis, which will be included in the environmental impact statement mandated by the National Environmental Policy Act.  The fish and aquatic effects analysis will also inform a biological assessment that the federal fish agencies will use to determine whether proposed modifications to the long-term operations will jeopardize listed species and whether the proposed modifications are acceptable under federal law.

The review will evaluate the approach and methods adopted by Reclamation to assess how the long-term operations might affect the aquatic environment, the exposure response, and the risk to select Endangered Species Act-listed species.  The panel of five experts will review the project’s materials and produce a panel letter review.  The review process is anticipated to start in early fall, with a review letter available in late 2023.

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