By Roy L Hales

Though British Columbia’s hydrologists have fifty years of stream flow data to formulate its’ responses to climate change, a recent study from the University of Victoria shows this is not enough. Tree ring data shows that, since 1658 AD, there have been 16 droughts exceeding anything evidenced in the instrumental record. The most recent and severest of  these events took place in 1958. According to one of the study co-authors, Bethany Coulthard, “It was a cool time and yet we still saw these extreme natural droughts.” Add problems like urbanization, deforestation and rising Global temperatures into the equation and we can expect a mega-sized drought coming to BC.

Mega-Sized Drought Coming To BC

“Water managers, in the province and elsewhere, have been using 50-60 year instrumental snapshots of what is the worst case scenario and that snapshot does not show us how severe droughts can be.  We are underestimating how severe a natural drought would look,” said Coulthard.

She added, “When you look at how severe droughts can get and then you add climate change and land use change on top of that, it would be reasonable to expect that when one of these extreme events does happen it will be more severe than anything that has happened in the past 350 years. We will almost certainly experience droughts worse than last year in the decades to come.”

Impacts on salmon

This could have catastrophic consequences on the province’s salmon population.

Last summer, for example, stream temperatures on Cortes Island were reaching the threshold of being untenable for fish.

“It is very possible that 2014 and 2015 were the worst droughts on record … We couldn’t include those years in th analysis we did because we didn’t have stream flow data yet from the province … but, based on the historical reconstruction, we can expect worse than that, ” said Coulthard.

The good news is that the streams that will be most effective are also small enough that local communities can take action to reduce risk.

Coulthard said she was inspired by the way that communities like Cowichan responded to that drought by cutting back their water usage.

A Very Strong Model

She  and her colleagues used tree ring data from the Sable, Chemainus and Zeballos Rivers on Vancouver Island, as well as Kanaka Creek near Vancouver in the Lower Mainland. They tested  their reconstruction by comparing it to the instrumental record during the years where their chronologies overlap.

“Its’ a very strong model, the strongest that has ever been developed for the province … Trees are limited by lack of moisture, their rings are proportional to how much moisture is available..”

In the University of Victoria’s press release, it explains:

” … The smaller the tree rings, the more extreme the conditions, such as low snow depth and a hot summer. Streamflow records are short and don’t usually catch the most extreme droughts, while tree-ring records give a longer, more accurate snapshot and, in addition, the province’s small watersheds can have high runoff one year and very low runoff the next—all of which can mislead planners and the public into thinking one strong streamflow year signals safety from drought.”

There Is Hope

Though conservation strategies are not her area of expertise,  Coulthard says there is hope.

“Individual choices on water use and water conservation can have a measurable impact on keeping water in streams, especially during the acute low summer flow season,” she said.

“On the South Coast, the streams that are most susceptible to these droughts … are relatively small … That could be a drawback in that you have to react quickly, but it also might make the situation more manageable in terms of physically relocating salmon or … stream level problems that can be addressed by local communities.”

Coulthard and her co-authors will be touring the province in June. The team will also meet with the Cowichan Valley Water Management Board and Cowichan First Nation has invited them to come stay. Coulthard thinks they may end up having a panel discussion and bringing in some other experts to discuss long term strategies.

“They can make real measurable change by changing their water extraction licenses and flow release policy,” said Coulthard.

Coulthard will be giving a report about possible strategies to the  Sunshine Coast Regional District.

They will also meet with the Sunshine Coast Regional District and the B.C. Government’s hydrologist.

“Different communities will probably need to take different approaches based on the nature of their watershed, population size, etc. I would recommend taking drought management very seriously, and consulting with a professional water manager with the goal of designing a water management strategy that is resilient to severe drought,” said Coulthard.

The Report

The report is available on ScienceDirect.com and was originally published in the Journal of Hydrology. It is co-authored by geographer Dan Smith, who leads the UVic Tree Ring Laboratory, and David Meko of the University of Arizona. Coulthard is a research associate in the lab and a postdoctoral scientist at the University of Arizona.

This research was supported by an NSERC Discovery Grant, an NSERC Alexander Graham Bell Canada Graduate Scholarship-Doctoral (CGSD), and an NSERC Michael Smith Foreign Study Supplement.