Forest fires increasingly affecting rivers and streams – for better and worse

An image of the Bitterroot River Montana forest fire

Bitterroot River Montana forest fire. Image credit: John MacColgan/Creative Commons

UCLA-led study finds greater ‘streamflow’ may mean more water for the West, but could increase risk for floods, landslides

By Anna Novoselov

Forest fires can have a significant effect on the amount of water flowing in nearby rivers and streams, and the impact can continue even years after the smoke clears.

Now, with the number of forest fires on the rise in the western U.S., that phenomenon is increasingly influencing the region’s water supply — and has increased the risk for flooding and landslides — according to a UCLA-led study published today in the Proceedings of the National Academy of Sciences.

Researchers examined streamflow — a measure of water volume over time in rivers and streams — and climate data for 179 river basins. (Basins are areas of land where precipitation collects and drains into a common outlet.) All of the areas were located in the western U.S., and all had been affected by forest fires between 1984 and 2020.

Using a mathematical model they developed, the scientists discovered that streamflow in the years after a fire tended to be higher than scientists would expect based solely on climate conditions, and that larger fires tended to be followed by larger increases in streamflow.

In basins where over 20% of the forest had burned, streamflow was 30% greater than expected based on climate conditions, on average, for an average of six years.

Park Williams, a UCLA associate professor of geography and the study’s lead author, said forest fires enhance streamflow because they burn away vegetation that would otherwise draw water from soil and block precipitation before it ever reached the soil. Intense forest fires can also “cook” soils, making them temporarily water repellent.

From 1984 through 2020, the amount of forested area burned each year in the West increased elevenfold, and that trend is expected to continue or even accelerate due to climate change.

“As a result, we’re starting to see sequences of years when large portions of forest are burned across some very important hydrological basins such as those in California’s Sierra Nevada,” Williams said.

The study’s findings suggest that wildfires will soon become yet another important consideration for those in charge of the supply and distribution of water resources. Each year, the region’s water managers must carefully calculate how much water will be available and determine how to conserve and allocate it.

In one sense, the increase in streamflow from forest fires may be beneficial, Williams said.

This could come as good news to dry cities like Los Angeles, because it could actually enhance water availability,” Williams said.

But other outcomes could be troubling. For example, in the coming decades, too much water could overwhelm reservoirs and other infrastructure, and could increase the risk for catastrophic flooding and landslides in and around burn areas.

To adapt to increasing flood risks, Williams said, water managers in California may have to lower the water levels in reservoirs in the fall and winter to make room for excess water from major rainfall and snowstorms. Such a strategy could avoid disastrous flooding in some cases, but it could also put communities at risk for having too little water during the state’s increasingly hot, dry summers.

Water after a forest fire also tends to be heavily polluted, carrying mud, debris and large sediment loads. So even if the quantity of available water increases after a large fire, it’s likely that water quality will worsen.

Williams said he hopes the findings help water managers and climate scientists make better predictions about water availability and flood risk.

“Water is a really heavy and destructive thing,” Williams said. “It’s great when it comes to us in the expected amount. It is catastrophic when it shows up unexpectedly.”

This article originally appeared in the UCLA NewsroomFor more news and updates from the UCLA College, visit

Megadrought in southwestern North America is region’s driest in at least 1,200 years

Image of parched land in Nevada

Parched land in Nevada. A UCLA-led research team studied centuries of megadroughts in the region spanning southern Montana to northern Mexico and the Pacific Ocean to the Rocky Mountains. Photo credit: Famartin/Wikimedia Commons

Climate change is a significant factor, UCLA-led research finds

By Anna Novoselov

The drought that has enveloped southwestern North America for the past 22 years is the region’s driest “megadrought” — defined as a drought lasting two decades or longer — since at least the year 800, according to a new UCLA-led study in the journal Nature Climate Change.

Thanks to the region’s high temperatures and low precipitation levels from summer 2020 through summer 2021, the current drought has exceeded the severity of a late-1500s megadrought that previously had been identified as the driest such drought in the 1,200 years that the scientists studied.

UCLA geographer Park Williams, the study’s lead author, said with dry conditions likely to persist, it would take multiple wet years to remediate their effects.

“It’s extremely unlikely that this drought can be ended in one wet year,” he said.

The researchers calculated the intensity of droughts by analyzing tree ring patterns, which provide insights about soil moisture levels each year over long timespans. (They also confirmed their measurements by checking findings against historical climate data.) Periods of severe drought were marked by high degrees of “soil moisture deficit,” a metric that describes how little moisture the soil contains compared to its normal saturation.

Since 2000, the average soil moisture deficit was twice as severe as any drought of the 1900s — and greater than it was during even the driest parts of the most severe megadroughts of the past 12 centuries.

Studying the area from southern Montana to northern Mexico, and from the Pacific Ocean to the Rocky Mountains, researchers discovered that megadroughts occurred repeatedly in the region from 800 to 1600. Williams said the finding suggests that dramatic shifts in dryness and water availability happened in the Southwest prior to the effects of human-caused climate change becoming apparent in the 20th century.

Existing climate models have shown that the current drought would have been dry even without climate change, but not to the same extent. Human-caused climate change is responsible for about 42% of the soil moisture deficit since 2000, the paper found.

One of the primary reasons climate change is causing more severe droughts is that warmer temperatures are increasing evaporation, which dries out soil and vegetation. From 2000 to 2021, temperatures in the region were 0.91 degrees Celsius (about 1.64 degrees Fahrenheit) higher than the average from 1950 to 1999.

“Without climate change, the past 22 years would have probably still been the driest period in 300 years,” Williams said. “But it wouldn’t be holding a candle to the megadroughts of the 1500s, 1200s or 1100s.”

As of Feb. 10, according to the U.S. Drought Monitor, 95% of the Western U.S. was experiencing drought conditions. And in summer 2021, according to the U.S. Bureau of Reclamation, two of the largest reservoirs in North America — Lake Mead and Lake Powell, both on the Colorado River — reached their lowest recorded levels.

Regulators have continued to implement water conservation measures in response to water shortages caused by the drought. In August, for example, federal officials cut water allocations to several southwestern states in response to low water levels in the Colorado River. And in October, California Gov. Gavin Newsom declared a drought emergency and asked Californians to voluntarily decrease their water usage by 15%.

Williams said initiatives like those will help in the short term, but water conservation efforts that extend beyond times of drought will be needed to help ensure people have the water they need as climate change continues to intensify drought conditions.

The study was a collaboration among researchers from UCLA, NASA and the Columbia Climate School.

This article originally appeared in the UCLA NewsroomFor more news and updates from the UCLA College, visit

Days with hazardous levels of air pollutants are more common due to increase in wildfires

In Western U.S., health risks from ground-level ozone and fine particulate matter continue to grow, study shows

Image of smoke from a wildfire turning the sky orange-brown in Los Angeles’ Mar Vista neighborhood.

In October 2017, smoke from a nearby wildfire turned the sky orange-brown in Los Angeles’ Mar Vista neighborhood. Photo credit: Sean Brenner

By David Colgan

After decades of air quality improvement due to the Clean Air Act of 1970 and other regulations since, the Western U.S. is experiencing an increase in the number of days with extremely high levels of two key types of air pollutants due to climate change.

From 2000 to 2020, the growing number of wildfires — made more intense by climate change — and the increasingly common presence of stagnant, hot weather patterns combined to increase the number of days with hazardous levels of ground-level ozone and fine particulate matter. Those conditions are creating health risks for people throughout the region, according to a paper published in Science Advances.

Daniel Swain, a UCLA climate scientist and co-author of the paper, said the increased pollution affects densely populated regions across a broad swath of the West, including the Los Angeles basin, Salt Lake City, Denver and Oregon’s Willamette Valley. The study found that the number of days when both pollutant levels were extremely high increased in nearly every major city from the Pacific Coast to the eastern Rocky Mountains. (The scientists judged pollution levels to be “extremely high” on days when they were in the 90th percentile of their daily average for the study’s 20-year span.)

Smoke from wildfires can travel thousands of miles, harming people who don’t live directly in wildfire-prone areas.

“When we looked at satellite imagery of the whole country this past summer, we could see smoke from Western wildfires making it all the way to New York City,” Swain said. “There could be a connection with air pollution as far away as the East Coast.”

Wildfires and stagnant, hot weather patterns increase the presence of pollution classified as PM 2.5 — particles that measure less than 2.5 microns in width, the equivalent of about three one-hundredths the width of a human hair — which can make its way deep into lungs and can cross into the bloodstream. Scientific studies have linked PM 2.5 pollution to health problems such as decreased lung function, irregular heartbeat and even premature death in people with heart or lung disease.

The combination of weather patterns and wildfires also increases the formation of ground-level ozone, another threat to respiratory health. Ground level ozone forms due to chemical reactions between oxides of nitrogen (such as nitric oxide and nitrogen dioxide) and volatile organic compounds, both of which can come from vehicles, power plants, industrial facilities and other sources.

The researchers found that the increase in extreme levels of PM 2.5 due to climate factors increased hazardous air quality conditions by an average of 25 million person-days each year of the past two decades in the Western U.S. and adjacent areas of the Great Plains, Mexico and Canada. (A person-day refers to a single day of exposure by a single person.)

The analysis is based on pollution data from U.S. Environmental Protection Agency monitoring sites, as well as atmospheric observations and data on atmospheric pressure and temperatures.

The poor air quality conditions highlighted in the paper are likely to get worse for at least the next few decades, even if drastic climate change mitigation measures are implemented, Swain said.

“It has gotten hotter, wildfire conditions have gotten worse and we’re seeing more persistent periods of high atmospheric pressure,” he said. “Each of those factors is projected to increase in the coming years.”

While mitigating emissions from wildfires and climate change will take decades, cities could still enact regulations and other programs to that would help reduce the presence of oxides of nitrogen and volatile ogranic compounds — so-called ozone precursor emissions — in the near term. Although the benefits of those changes would take years to accrue, it could be practical for cities to implement emissions-reduction measures during periods of hazardous air quality, and it would likely help reduce the dangers to human health, Swain said.

This article originally appeared in the UCLA NewsroomFor more news and updates from the UCLA College, visit

Divers survey submersible cages used to farm cobia off the coast of Puerto Rico. UCLA researchers conducted the first country-by-country evaluation of the potential for marine aquaculture under current policies and practices.

Will ocean seafood farming sink or swim? UCLA study evaluates its potential

Divers survey submersible cages used to farm cobia off the coast of Puerto Rico. UCLA researchers conducted the first country-by-country evaluation of the potential for marine aquaculture under current policies and practices.

Divers survey submersible cages used to farm cobia off the coast of Puerto Rico. UCLA researchers conducted the first country-by-country evaluation of the potential for marine aquaculture under current policies and practices.


Seafood farming in the ocean — or marine aquaculture — is the fastest growing sector of the global food system, and it shows no sign of slowing. Open-ocean farms have vast space for expansion, and consumer demand continues to rise.

As with many young industries, there’s a lot to figure out, from underlying science and engineering to investment and regulations.

In a study published in the journal Marine Policy, UCLA researchers report that they have conducted the first country-by-country evaluation of the potential for marine aquaculture under current governance, policy and capital patterns. They discovered a patchwork of opportunities and pitfalls.

Peter Kareiva, one of the study’s authors and director of the UCLA Institute of the Environment and Sustainability, said sustainable food systems are an important part of the fight against climate change.

“Like many environmental scientists, I see marine aquaculture as the future food system for a carbon neutral world,” Kareiva said. “But whether we get that future and a healthy ocean depends on governance and regulations — and we all know how sketchy those can be at times.”

In 2017, Kareiva’s research found that a tiny fraction of the world’s oceans, farmed sustainably — just 0.015 percent — could satisfy the entire world’s fish demand.

The new study categorizes 144 countries into three groups based on their capacity for aquaculture growth in the industry: “goldilocks,” “potential at-risk” and “non-optimized producer.” The categories are based on quality of government institutions and regulations, potential for investment and how suitable the biological and physical environment are for farming seafood in the ocean.

Sixty-seven countries fell in the goldilocks category for either finfish or bivalves, like mussels and clams — meaning conditions there are favorable for marine aquaculture. According to lead author Ian Davies, who conducted research for the study at Kareiva’s UCLA lab, the industry could help address social challenges in these places.

“There is a lot of potential in food-insecure countries, including island states in the Pacific and Caribbean,” Davies said. “They have limited resources and quickly growing populations. But these are also the countries with the most productive waters in the world.”

Twenty-four countries were identified as non-optimized producers, which lack highly productive waters but still engage in aquaculture, usually because of better access to investment. This group includes countries around the Persian Gulf and Black Sea, South Korea, Italy, Canada and Norway.

Finally, the paper categorized 77 countries as potential at-risk. These countries have suitable waters but poor access to capital and unstable, corrupt or ineffective governance systems. Despite such problems, 16 are currently farming fish in the ocean, often harming ecosystems or causing other problems in the process. China is by far the largest producer of ocean-farmed seafood, owing to strong financial capacity and political will, but was found to have poor oversight — which could pose problems for the industry in the future.

“The more robust regulation you have, the more you can ensure the industry will be around for longer, and that it will be able to produce fish at a reasonable cost with minimal input,” Davies said. “There is a palpable feeling among planners, researchers and aquaculture operators that we have the ability to do this right before the industry gets too big. Let’s put the regulations in place.”

Ineffective regulation often leads to ecosystem damage. In the 1990s, there was a shrimp farming boom in Southeast Asia. Operations added too much shrimp and feed to mangroves, destroying many in the process. The impact was also felt by humans. Mangroves serve as barriers that reduce storm surge and flooding, and many small aquaculture operators quickly found themselves out of business. More recently, unregulated fish farming led to disease outbreaks in northern Vietnamese waters.

In other observations, the study found that while lack of regulation poses problems, so can regulation that is too burdensome. In Ireland the licensing process takes years, making it impossible for operators to qualify for European Union grants. There are other country-specific barriers, too. New Zealand is a goldilocks country, but opposition from local communities and vocal stakeholders, including fishermen, has slowed marine development.

China is the largest marine aquaculture producer by far, but its waters are only moderately good and its governance was listed as low quality. The industry has succeeded there because of political will and access to capital. China isn’t alone. Excluding outliers, the study notes, less suitable countries produce almost six times as much fish as optimal countries. Capital-driven aquaculture in less suitable waters carries the risk of being less effective and more damaging.

Marine aquaculture is seen as promising compared to high-polluting inland operations. The open ocean disperses its impact, leading to fewer environmental problems. Meanwhile, according to the United Nations, nearly 90 percent of the world’s marine stocks are depleted, with many fisheries on the verge of collapse. Sustainably farming oceans could allow wild populations to rebound while serving as a crucial source of protein and economic benefits to humans.