The tale the trees tell: droughts will be worse in BC

BC should plan for worse droughts than previously expected

Combined with the impacts of climate change and deforestation, the coastal regions of southern BC are very likely to be hit by a worse drought within the coming decades than any time in the last three to four centuries, according to a new report co-authored by graduating PhD student Bethany Coulthard at the University of Victoria.

Using 350 years of tree ring data as well as long-term drought records, Coulthard found at least 16 historical droughts worse than the benchmarks used today by hydrologists and water managers in coastal BC. “We have underestimated both how common and how severe the worst droughts are in this part of BC,” she says. “If we don’t implement more conservative mitigation strategies, the region will be seriously underprepared when one of these droughts hits. The impacts would be disastrous for stream ecology and salmon.”

She and her collaborators discovered that 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. Coulthard is meeting with BC provincial planners next month to discuss drought predictions and modelling.

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.