Why a summer of drought could lead to fall flooding in B.C.

After a summer marked by prolonged drought and record-breaking wildfires, B.C.'s landscape has been left more vulnerable to floods and landslides, according to an expert.

UBC Prof. John Richardson told CTV Morning Live that while rainy weather brings some relief, it also brings risk – particularly if the precipitation is sudden and heavy.

"We're still talking about these atmospheric rivers, which nobody talked about five years ago. And that means that we have these really focused streams of moisture that are coming at us," he explained.

Both drought and wildfires, Richardson says, change the soil and make it less absorbent which means waters flow directly into rivers and streams. This summer's drought, he also notes, is the second year in a row the province has seen persistently parched conditions.

"Anytime we have big, big rains, we have to be concerned about those sorts of things, but the things that have happened in the last couple of years are going to lead to the landscape being a little bit more vulnerable to that rainfall," he said.

The other thing that the drought has done to rivers and streams is to clog them with twigs, branches and other debris. And brittle, drought-stricken trees are likely to lose more branches in windy conditions.

"The streams not only will have water rushing through them, but there's a lot more stuff out there in terms of twigs and things that get washed out. And as they move down, they can dislodge logs and rocks and eventually we could end up with small debris avalanches," Richardson said.

Wildfires also destabilize the roots of trees and burn surface vegetation, he said.

"The soil is no longer protected by the roots of the trees that hold the soils together. And especially in steep landscapes, that combination can lead to more landslides," he added.

Richardson also said he doesn’t think there is a risk of a repeat of the catastrophic flooding that devastated parts of the province in 2021 and he does not predict that "the whole province is going to slide into our streams but we're going to have more landslides."

However, he also said that the places most vulnerable to flooding and landslides are the ones that have already been hardest-hit by wildfires and drought.

In the last update from provincial officials on drought conditions, 80 per cent of the province's watersheds were at drought level four or five. This means that "adverse impacts on both communities and ecosystems" are likely or almost certain, according to the province's ranking system.

The wildfire season has seen an unprecedented number of hectares scorched, tens of thousands evacuated and hundreds of properties lost. It has also been a devastating one for firefighters, who have seen six of their colleagues die.