APRIL 2018 • COUNTRY LIFE IN BC


13


Above-normal snowpacks cause for concern Flood predictions premature but heavy rain and warm temperatures could be bad news


by TOM WALKER VERNON – The only thing for certain is


uncertainty. Spring is coming, there’s been lots of snow in the mountains, and it’s going to melt. It’s anyone’s guess how quickly. “Yes, it’s really deep,” agrees an


Okanagan cattle producer Werner Stump. “Probably the most I’ve seen. It’s up to the top wire on my fences.” Asked about the probability of


flooding, he very politely shook his head. “There is absolutely no way of


predicting,” he commented. “We just have to wait and see what the weather does.” Dave Campbell, head of the BC River


Forecast Centre agrees. “When we look at how snowpacks


develop through the year, it certainly gives an idea about how much water is stored,” says Campbell. “Obviously, that is the amount of water that has to come down, but as we get into the melt season, it really is dependent on the day-to-day weather. “Do we get extreme heat that melts the snow


quickly or do we get heavy rain? In years when we have high snowpacks, we can see things go either way based on the weather. We can see areas that we can interpret to have very high risk but the weather co-operates and we don’t see flooding and, conversely, we can have years where the snowpack is looking fairly benign and we have these adverse weather patterns that lead to flooding.” “At this stage, our job is to identify what those


risks are. It’s not really a prediction about whether it’s going to flood or not,” he adds. Campbell points to 1999 as a “benchmark year”


for the provincial snowpack but not necessarily a big flood year.


“2007 was another one where we had pretty high


snowpacks and fairly high flows, but not the flooding,” he adds. “It’s probably only about a 20% chance that we will see flooding with a really high snowpack,” he


caused the higher snowfalls this past winter are likely to hang around for the next couple of months. While 80% of the yearly snowpack typically accumulates by early March, there is potential for increasing snowpacks over the next four to eight weeks, increasing the flood risk across the province.


That is certainly what happened last


year in the Okanagan. From 86% of normal in March, snow


levels continued to rise to a high of 228% by June 1. That snow fell as rain at lower elevations, filling creeks and further saturating soils that had soaked up very high fall rains. Inflows to Okanagan Lake were early and higher than normal (240% of normal in May and the highest observed in 96 years). A recent review of the Okanagan


MYRNA STARK LEADER PHOTO


says. But he does note that the whole southern half of the province is “above that threshold where we start to expect to see that increased risk.” As of March 1, snowpacks were 144% of normal in the Similkameen, 141% in the Okanagan, 136% in Boundary and 135% in the Skagit. The West Kootenay region is at 127% of normal with East Kootenay at 120%. Upper Fraser West is at 138% while the overall Fraser River basin is moderately above normal. The Lower Fraser, at 122%, increases the flood risk on the Lillooet River which flows through the Pemberton Valley. Knowing what to expect next can be a problem. Seasonal weather forecasting is very challenging, particularly when it comes to rainfall, Campbell notes. “Even temperature is difficult,” he says. “One of the patterns that help with seasonal forecasting are ocean temperature and pressure patterns that develop in La Niña and El Niño. years.” Campbell says the La Nina conditions that have


flood response published by the BC Ministry of Forest, Lands and Natural


Resource Operations notes that by mid-May, the Penticton dam was releasing the maximum water possible. Increasingly hot weather in May and June brought on the snowmelt and there was nowhere for it to go. This year, it is more clear that there is going to be an elevated volume coming from the snow, Campbell says, and the Penticton dam is releasing more water than usual. But, he notes, too much too early can put lake levels below normal causing fishery, water supply and irrigation issues. Keep an eye out but don’t be worried yet, says


Campbell. “In a normal year, it isn’t until the middle of April


that we start to get into the wholesale melt,” he says. “I know there has been a lot of concern with this warm weather (mid-March) but it is quite early. We need to get up into the 25-degrees range for several days to get any flood-concerning melt going on, so the season doesn’t start up for at least another month. “


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