Water inundates homes in the Okanagan, a region hit by wildfires in 2017. Regional District of Okanagan-Similkameen
Environment

Newsletter: Why big wildfires lead to bad floods.

Lauren Kaljur May 19, 2018

As I write this, thousands of people in B.C. are following evacuation orders in response to some of the worst flooding in 100 years. Many of these communities are still recovering from the unprecedented wildfires last summer.

Is this a tragic coincidence? Unfortunately not.

Where there’s high intensity wildfire, serious floods can follow — in some cases more damaging than the wildfire itself.

How is this possible?

  • Healthy forests are nature’s sponges. Trees and all of the life connected to it absorb water and release it gradually.
  • When vegetation is devastated by a big wildfire, “burn scarred” soil and torched trees become less sponge-like and actually repel water.
  • As spring rains fall, water pools and overwhelms streams and rivers — leading to more extreme flooding, erosion and landslides (around a hundred times the normal rate).
  • As science communicator Sarah Boon explains in her blog and in a great article, snow also packs deeper after major wildfire. A deep and exposed snowpack then melts quickly and all at once as it’s exposed to sunlight — also overwhelming watersheds.
  • The final kicker: Flash flooding and melting snow don’t protect us from wildfire, or water shortages. Too much water all at once can lead to drought. These extreme weather events combined are dubbed climate change “whiplash.”

See it for yourself

Regions of the province that saw the highest snowpack this winter were hit by wildfires last summer — and most of these regions are also experiencing major floods. Think of it this way:

The unprecedented 2017 wildfire season in B.C. left behind roughly 1.2 million fewer hectares of healthy forest to retain and control water. The linkage between these extreme events is such a big deal, B.C.’s independent review of the 2017 wildfires and floods specifically highlights it. On top of this, we know major wildfires, heavy rainfall and floods are part of a climate-changed reality. Given that Canada is warming at twice the global rate, this should be cause for pause.

What can we do about it?

The government is well aware of the connection between fires and floods, and encourages homeowners to prepare for and understand the risks. But what can be done to lower the risk in the first place? Beyond storm warnings, areas hit by major wildfire can be assessed and treated to reduce risk from flooding before it happens.

The province conducted 40 post-wildfire risk assessments last year, and made recommendations to municipalities and First Nations for things like installing culverts or channeling streams. But scientists are uncovering other ways to help this process at the forest-level, like dropping seeds and mulch from helicopters. The problem is, this costs money. And every time a major wildfire hits, more money is spent on wildfire response instead of prevention.

What’s also clear is we need more controlled burns, as I outlined in the last Fire Break. Controlled, low-intensity fires leave behind a living forest, healthy and able to absorb water and withstand the next major wildfire — and flood.

Have your say.

What else do you want to know about wildfires? What should the next Fire Break be about? You can submit your suggestions here or via email, Facebook and Twitter.

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