DATA: Fraser Valley summers are twice as dry than 30 years ago

If summers seem particularly dry these days, that’s because they are.

The amount of rain falling each July and August in the Fraser Valley has dramatically declined over the last two decades, according to six decades of weather statistics obtained and analyzed by The Current.

The cause is uncertain—although global climate change would seem the most likely culprit, other data suggests that may not be the case.

With no clear cause, we don’t know if the current trend will continue. But what is certain is that at the moment, summer rain is becoming scarcer, with implications for everything from fish to agriculture to the supply of water and your property tax bill.

Summers are almost always the driest time of the year in the Fraser Valley, but some years—and decades—are much drier than others.

Right now, the valley is in a decade-long dry summer spell. Particularly dry summers are now quite common. And rainy weeks in July and August is mostly a thing of the past. (Annual precipitation totals haven’t changed as much because more rain has been falling in winter months.)

The data is pretty clear. In the 1970s, on average, around 117mm of rain fell in Abbotsford every July and August. In the 1980s and 1990s, around 90mm of rain fell each year. But in the past 10 years, July and August rainfall has been half that—with an average of just 45mm falling each year.

It’s been more than a decade since Abbotsford recorded more than 100mm of rain during July and August. In place of those frequent rainy summers, we now see incredibly dry spells. In 2017, only 8mm of rain was recorded. In 2018, 31mm fell. And last year, just 12mm hit the ground.

The rainiest July and Augusts in the past decade—2015 and 2020—in which 95mm of rain fell, would have been just typical years as recently as the turn of the century.

The data comes from precipitation figures provided to The Current by Environment Canada. In addition to readings at Abbotsford, The Current obtained data for stations in Hope and Vancouver, though precipitation data in Hope is absent between 1995 and 2012.

*In some recent years, data for a handful of days at each station are missing. For such years, The Current has used a daily average of precipitation to project a full comparable July-August total.

Precipitation totals for both Hope and Vancouver mimic that seen in Abbotsford—as would be expected given the shared Lower Mainland climate. Vancouver has experienced a slower decline in precipitation totals since the 1980s. Hope has seen an even more precipitous decline.

In the 1980s and 1990s, Hope and Abbotsford had significantly wetter summers than Vancouver. Precipitation patterns have converged, however, and all have recorded similar rain totals over the past decade.

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An uncertain cause

Climate change has significantly and consistently increased temperatures across the Lower Mainland for decades. Those increasing temperatures can be tied to extreme heat events and more common wildfires.

But temperature and precipitation patterns are not entirely linked, and—unlike its clear responsibility for rising temperatures—climate change may not be to blame for changes in localized seasonal rainfall.

The Current forwarded the data to Charles Curry, the acting lead of regional climate impacts at Pacific Climate Impacts Consortium. Curry used the figures and paired them with similar data from the ERA5 global reanalysis—the pre-eminent set of global and local weather and climate data.

Curry noted that while summer precipitation in the Lower Mainland had indeed declined in recent decades, prior to that, rainfall amounts had increased.

“While the summer drying trend since 1990 is consistent with the strong warming seen over the same period, we should note that the pre-1990 behaviour also occurred in tandem with local warming,” Curry wrote. “So there may be other explanations for trends in precipitation that only last a decade or two, such as ocean temperature variability.”

In other words, the last 70 years have seen temperatures only go in one direction: up, as would be expected given climate change. But Lower Mainland rainfall amounts both rose significantly, and also fell, and are now close to where they were in the mid-1900s. That suggests another factor is influencing how much rain falls here each summer. Because we don’t know what that factor is, we don’t know if or when the current drying trend may stop or reverse itself.

Consequences

That’s not to say climate change isn’t having an impact. Indeed, it’s likely aggravating the consequences of less rain. Warmer temperatures accelerate evaporation, and so when some rain does fall in 2023, the warmer temperatures dry out vegetation and the ground quicker than in the 1900s.

And the Fraser Valley is warming fast—faster, indeed, than Vancouver. In 2020, in Abbotsford had increased by 1.5 C since the 1970s, aster than the rate of warming in Vancouver.

The two factors—higher temperatures and less summer rain—are aggravating one another, and changing the way Fraser Valley residents experience—and prepare for—summer. (The Current did not analyze precipitation trends in the Interior of BC.)

The drier summers are leaving forests (and roadside grass) more fire prone, resulting in wildfires like that which threatened the community of Laidlaw outside of Hope last year. Farmers are having to use more water to irrigate their crops. And less rain in watersheds that supply drinking water to Fraser Valley communities will increase the pressure on those resources—and potentially the need to build costly new infrastructure.

Drier summers are also decreasing the amount of water in rivers and streams. That allows the water that is present to warm more quickly. The combination of less rain and warmer temperatures is a dangerous mix for rivers, streams, and wetlands and their occupants because the warmer water can threaten or compromise the health of salmon and other fish and lifeforms.

The Fraser Valley’s drought era is upon us.