Fire and rain

Fire and rain

Understanding how erosion and floods affect post-forest-fire watersheds could save lives and millions of dollars
March 1, 2006
As record breaking forest fires raged across B.C. in the summer of 2003, praying for rain became a popular pastime. But when the rain finally hit in mid-October, it brought with it new problems including floods, mudslides, and contaminated drinking water.

Usually the region’s watersheds, areas of land draining down to rivers or lakes, are able to absorb heavy rain. But mountain slopes burned bare by the wildfires could not slow the raging water as it washed soil, trees, and other debris down the mountains. The week-long rains left four people dead, forced 1,200 to abandon mud-filled homes, and washed out bridges and highways. Damage reached tens of millions of dollars.

“The year 2003 was a fire season from hell, and these events could become more frequent if global warming leads to more fires. We need to be better prepared,” says David Scott, an assistant professor at the University of British Columbia Okanagan (UBC-O). Through his work as a Forest Renewal British Columbia Research Chair in Watershed Management, Scott is exploring how to protect watersheds from the effects of forest fires.

Forest fires burn trees, other vegetation, and ground-covering litter that would normally slow and hold rainwater—that’s the obvious effect. But forest fires also heat and char the soil, leaving it more vulnerable to erosion and unable to absorb water normally.

This effect is familiar to anyone who has seen water form a puddle in the ashes of a campfire. Scott describes it as “fire-induced water repellency.” Charred soils don’t soak up water, leading to a “tin roof effect” where the rainwater remains on the surface without penetrating the earth below.

Scott was the first to scientifically document the water-repellent soils in B.C. after the 2003 fires. Most of Scott’s work focuses on ways to help soil absorb and slow down water flow after a forest fire. Dropping straw mulch from a helicopter is one promising idea. The mulch absorbs the water and gets spread by the wind from the helicopter rotors. For now, Scott relies mainly on student research assistants to haul straw mulch on their backs to the research plots.

Mulching dead trees after a fire and spreading them along waterways is also delivering results. Dropping grass seed from helicopters is a third treatment being tested. But Scott says that the burned site remains vulnerable to erosion during the time it takes for seeds to sprout and grow enough to provide reasonable ground cover. He also points out that the amount of rain doesn’t have to be exceptional to tip the balance and cause flooding and other problems.

To measure the effectiveness of his slope stabilization treatments, Scott relies on silt fence traps that stop the soil from being carried away by rainwater. He also uses gauges that measure rainfall depth and intensity to understand the energy driving erosion.

Scott hopes his research will change how we respond to the deadly combination of forest fires and rain. “We really are focusing on cheap and practical solutions that will work on a big scale, so we can help reduce the risk of erosion and flooding the next time there is a big forest fire,” he says.


Water is life. Every day, each of us needs about 2.4 litres of water. But even though water is the most precious commodity on the planet, we don’t manage our water supply very well.

High-profile incidents, like the tainted water tragedy in Walkerton, Ontario, grab headlines. Less dramatic news, such as reports from Environment Canada showing that 13 percent of Canadian municipal water is lost to leaks, rates barely a mention. But it all adds up to a pressing problem.

“We need to come up with more sustainable approaches. In the Okanagan Valley, for example, we could see serious water shortages within 25 years,” says Jeff Curtis, a professor in the Earth and Environmental Sciences Department at UBC-O. “Today, because of population growth, the Okanagan is a microcosm of the watershed management challenges Canada will face in the future.”

Curtis is stepping outside his traditional role as a researcher and looking at ways to incorporate water-related science into public policy. For example, some of Curtis’s work measuring contaminants in water and how they travel can help policy-makers decide where to source a community’s water supply. Using science to help guide water management decisions is gaining ground.

“New York City was faced with investing almost US$8 billion in a new filtration plant. Instead, they are investing a fraction of that in protecting and restoring upstate watersheds,” says Curtis.

To support this kind of public policy, UBC is building a multidisciplinary approach to watershed science. Drawing on a range of expertise makes sense when you consider the interconnected nature of the water cycle.

Working together, freshwater scientists, climatologists, chemists, biologists, fish ecologists, and soil ecologists will be able to take a “big picture” approach to managing watersheds. Part of this approach is aimed at helping communities to combat the erosion that threatens watersheds in the wake of forest fires. This erosion causes a variety of problems, including contaminated water that threatens fish habitats and human water supplies.

These UBC experts will likely find their work growing in importance as the stresses on our water supplies increase along with global population growth.

“Our research is targeted to help people think of water as a health-related resource, not a utility,” says Curtis.


The researchers at the UBC-O Earth and Environmental Sciences Department work closely with scientists at the B.C. Ministry of Forests and Range. They receive financial support from forestry companies Weyerhaeuser Canada, Interfor, Tolko Industries and Riverside Forest Products.

They also have contacts with smaller private-sector firms. With partners at Limnology Research, Curtis helped design a countertop concentrator that’s able to concentrate field water samples for analysis of contaminants.

Learn More

Learn more about the Government of Canada’s approach to freshwater management.

Forty quick facts about Canada’s water supply and how we use it every day.

Learn more about the world’s 106 major watersheds.

Visit the world lakes database.