2007-06-16

Flooding in future may be more frequent, scientists say

British Columbia's narrow escape from an expected disaster this spring is proof positive that flooding is unpredictable.

And even though floods are even more difficult to forecast on a year-to-year basis, experts are saying natural phenomena could make flooding a frequent occurrence over the long term in the province's watersheds.

This year's threat came from record snowpacks in the mountains that melted rapidly into the rivers below during very hot weather. Although northern areas along the Skeena and Nechako Rivers had floods, the Lower Mainland was largely spared due to a turnaround in temperatures and a lack of rainfall.

However, Mr. Murdock said, there are plenty of reasons to start thinking about how climate change could affect the frequency of flooding in the province. To begin with, he said, most climate-change models predict that by 2050, winters in British Columbia will be much wetter, a forecast echoed by several scientists.

One of the most drastic predictions is that flooding could increase on the lower Fraser River by 60 to 90 per cent as a result of the mountain-pine beetle's devastation of the tree stands that protect watersheds such as the Chilcotin, the Nechako and the Upper Fraser Rivers.

This was the result of a study conducted this year for the Forest Practices Board forest practices board in the Baker Creek watershed near Quesnel by Dr. Younes Alila of the University of British Columbia's forestry faculty.

When the pine beetles attacks a stand of pines, they trees go from green to red or brown, and then to grey. This takes several years, during which time the fine branches and needles drop, leaving only the trunks.

Sixty per cent of the trees in the Fraser River watershed are pine and on flat terrain, Dr. Alila said, and on flat terrain, making the river extremely vulnerable to increased peak flows due to pine-beetle damage. Right now, those trees are in the red or brown phases, and are still catching snow like healthy trees.

Damage from the beetle alone will cause flows to peak 60 per cent higher and two weeks earlier, according to Dr. Alila's research. However, if the pines are cut down, Dr. Alila predicts the flows will increase by 90 per cent and come 20 days earlier.

Dr. Alila points out, however, that there is a fine balance to be reached between the flooding threat produced by salvage logging beetle-infested trees, and the forest-fire threat produced by leaving them.