California’s forests are facing a growing threat: wildfires. The severity and frequency of these fires are on the rise, fueled by poor fire management practices, prolonged drought, and bark beetle infestation. These factors are only worsened by the changing climate, with hotter and drier summers, warmer winters, and a shift from snow to rain in precipitation patterns. As a result, wildfires in California are becoming more frequent, intense, and extensive, leaving a devastating impact on the state.
Fires occurring outside the Delta don’t directly affect it; however, there can be indirect impacts from fires in the Delta watershed, such as increased sediment and debris, runoff, fire retardants, dissolved contaminants, other water quality impacts, and poor air quality from smoke. To learn more about these impacts, the June meeting of the Delta Stewardship Council featured a panel discussion on wildfires.
The panel speakers were Dr. Cliff Dahm, former Delta Lead Scientist and professor emeritus at the University of New Mexico; Phil Crader, Assistant Deputy Director for the Division of Water Quality, State Water Resources Control Board; Dr. Teresa Feo, Senior Science Officer at the California Council on Science and Technology, and Dr. Amelie Segarra, assistant adjunct professor at UC Davis.
Wildfires are increasing in acres burned and intensity
Wildfires have risen dramatically in acres burned, with over 75% of the acres burned in the state’s 20 largest wildfires occurring since 2010. The fire season is now 80 days longer than 50 years ago due to earlier snowmelt and a thirstier atmosphere.
As wildfires become more frequent, their intensity is also on the rise. The most severe fires are causing significant damage to forests, resulting in extensive tree mortality. The picture on the left shows a surface fire, which typically moves slowly and remains close to the forest floor, consuming leaves, grasses, and small plants.
However, the picture on the right shows a crown fire, which burns far hotter and is far more dangerous. Crown fires occur when flames reach the tops of trees and rapidly spread from one tree to another, creating a wall of flames that can swiftly engulf an entire landscape. The more severe the fire, the more comprised the forests’ ability is to bounce back from fires and withstand prolonged drought conditions, as well as the cascading impacts of climate change.
Water quality impacts
The impact on water quality and the response of the watershed can vary greatly based on factors such as the size of the fire, the severity of the burn, the amount of vegetation burned, and whether the fire occurred in an urban or rural area. The amount and timing of subsequent precipitation and whether it is snow or rain also significantly determine the effects on water quality.
Numerous scientific studies have explored the effects on water quality after fires, including changes in turbidity, pH levels, levels of dissolved oxygen, and the presence of various chemicals such as organic carbon. Post-fire flows often contain substantial amounts of black carbon and increased levels of nitrogen, phosphorus, trace metals, and heavy metals. These factors can contribute to the growth of harmful algal blooms.
“Water quality generally responds fairly linearly with the amount of the watershed that burns,” said Dr. Cliff Dahm. “However, it responds rather exponentially in terms of the severity of the burn. So a severe burn has a much more likely negative effect on water quality. In fact, low-temperature fire or fire that does not crown out and produce a large amount of mortality can be a very beneficial part of the ecosystem. So there’s this fine line between being a water quality problem and a water quality help that is an important consideration when looking at wildfire effects.”
Physical impacts of wildfire on the landscape
Phillip Crader, Assistant Deputy Director of the Division of Water Quality at the State Water Resources Control Board, pointed out that wildfires can cause changes in hydrology and channel shape. The absence of plant cover results in less absorption of water and nutrients, causing them to flow across the land. This leads to an increase in surface water flow and movement of groundwater, which can result in unexpected springs emerging. These changes increase the risk of debris flows, slope failures, and other undesirable processes. Sometimes, it can separate the floodplains from the river’s main channel.
Downstream impacts
Wildfires have wide-ranging effects that extend beyond the burned area. The loss of vegetation leads to faster runoff, causing increased sediment and dissolved substances to be carried downstream. This can result in contaminants and debris, like logs and trash, settling in reservoirs and ecosystems. The impacts of this deposition can persist in water bodies and increase treatment costs for downstream drinking water systems for many years.
There is more effective precipitation that impacts habitat, such as sediments that can bury spawning gravels. Dissolved oxygen sags can move through, killing everything in its path, and excess nutrient loading in the upper watershed can lead to harmful algal blooms downstream.
Study to examine impact of fire retardant on species
Fire retardant is an effective tool for fighting wildfires, and just as wildfires have increased, so has the use of retardant, rising from 3.3 million gallons to 15.3 million gallons within five years. However, little is known about the impact of fire retardants on species and ecosystems.
Fire retardants can persist for several months on surfaces and can easily enter aquatic ecosystems through runoff or cleaning of the area. The risk of fire retardants entering aquatic systems increases if the wildfire occurs around a lake or a river. The potential impacts are concerning for the Delta since it is home to many threatened and endangered species and is a migration route for salmonids. Also, wildfire season corresponds with the migration period for fall-run chinook salmon.
To study the potential effects, the Delta Stewardship Council is funding a two-year study of the impacts of fire retardants on juvenile fish. The research, led by Dr. Amelie Segarra, an assistant adjunct professor at UC Davis, seeks to shed light on the risk and the potential impact on the early life stages of salmonids. These life stages were chosen for study because migration occurs during the wildfire period, and the earliest life stages are the most susceptible. The project has just gotten underway, with some results possible next year.
The role of the Water Boards
With the increase in wildfires, the Water Board has increased its response and has developed actions for before, during, and after wildfires.
Removing overgrown vegetation and creating defensible space are important activities, so the Water Boards worked with Cal Fire and the Board of Forestry and Fire Protection to develop a permitting program for activities that reduce wildfire risk. The program is automatically enrolling and free of charge for anybody in a covered area to go out and remove vegetation. The Board also worked with electric utilities and Cal Trans to clear right-of-ways and to reduce starts from automobiles. The Board also participates in the governor’s Wildfire and Forest Resilience Task Force.
During the fire, the Board has an emergency management team out on the ground, helping with response, communication, coordination, and getting BMPs in place to help protect water quality.
After the fire, the Board continues to help with emergency BMP deployments to protect surface water and vulnerable communities. The Board monitors water quality post-fire to help inform future management. The Board has streamlined permitting for debris removal and disposal so it can be removed before the next storm arrives. The Board coordinates and streamlines permitting for post-fire restoration projects and continues to participate in task force meetings.
Wildfire smoke
One far-reaching impact of wildfires just starting to be studied is the impact of wildfire smoke on near and distant communities. The graphic on the slide shows the average number of days per year the county was impacted by wildfire smoke in the last decade, which is increasing for virtually all counties. So even though direct wildfire risk might be very low in regions such as the Delta, the wildfire smoke and other impacts can travel far and be quite high.
Dr. Teresa Feo, Senior Science Officer with the California Council on Science & Technology (CCST), said they are partnering with Blue Forest Conservation on a peer-reviewed report examining wildfire smoke and its relationship to forest and public health. In particular, the report will consider the trade-off between increasing the beneficial fire to improve the resilience of the forest and the potential impacts of wildfire smoke. If we improve forest health with increased beneficial fire, will we see a net increase or reduction in wildfire smoke? Could making forests healthier actually result in a public health benefit?
The report will also include interviews with public health departments, health providers, and health insurers to better understand how wildfire smoke impacts communities near and far from wildfires and their information and data needs. The report is expected to be published in the fall of 2023.
The total cost of wildfires remains unclear
Just how much wildfires are costing the state has yet to be tallied, Dr. Feo noted. A 2020 report by the CCST synthesized the available science, research, and datasets to calculate how much wildfires cost California.
The report found that while we have good data on the fire suppression costs and insured property losses totaling billions to tens of billions of dollars annually, there are many wildfire impacts where data is insufficient for estimating the costs. These include the cost of health impacts from wildfire smoke exposure and the loss of ecosystem services due to water quality impacts. These impacts can affect communities downstream and downwind, sometimes hundreds of miles away. However, the existing data suggest that these costs are substantial, adding additional billions of dollars to the final tab.
“We don’t have the data we would need right now to really put a number to those impacts,” she said.
