Climate Change and the Columbia River Treaty

Written by Greg Utzig, P.Ag. Conservation Ecologist

Climate change, or more appropriately “climate disruption,” will bring significant changes to ecosystems and water management in the Upper Columbia Basin (UCB).  Some changes are already occurring, and the extent to which these changes will proceed depends on the success of global efforts to eliminate greenhouse gas emissions.

The climate of the UCB is a product of interactions between marine air masses off the Pacific, continental air masses from the north and east, and the mountain ranges within the Basin. Columbia River Treaty reservoirs in the West Kootenay (Arrow and Duncan) are more affected by Pacific weather systems, while Treaty reservoirs in the East Kootenay (Kinbasket and Koocanusa) are subject to increased influences from continental weather systems as well.  In general, the southern portion of Arrow and Koocanusa are the warmest and driest areas; northern Arrow, Duncan and mid/southern Kinbasket are the wettest; and northern Kinbasket is the coldest.

Climate change projections from Global Climate Models indicate increasing temperatures in all seasons for the whole UCB.  However, projected changes in precipitation are more nuanced. Annual precipitation is projected to increase, but the increases are not spread evenly across the seasons.  While spring, fall and winter precipitation are projected to increase, summer precipitation is projected to remain similar or decrease.  Although winter precipitation is projected to increase, the percentage of that precipitation that falls as snow is projected to decrease.  Overall water flows will increase in the winter and spring, and decrease in the summer and fall (see Figure 1).  Much of the U.S. portion of the Columbia Basin will see even more drastic changes, as it transitions from a snow-dominated system to a rain-dominated one.

Rising temperatures are already causing rapid loss of glaciers within the UCB, impacting late summer and fall flows in associated streams.  Higher summer temperatures and lower summer precipitation are also increasing the potential for drought stress and wildfire activity (see Figure 2).  As Canada and the U.S. seek to modernize the Columbia River Treaty, there may be opportunities to repair or improve certain ecosystem functions around Treaty reservoirs.  There is substantial research and river management modelling being led by the Ktunaxa, Secwépemc, and Syilx Okanagan Nations, in collaboration with provincial and federal agencies and consultants to see how different reservoir levels and river flows will affect a range of ecosystem values.  Climate change will have to be considered in any potential re-vegetation attempts within the reservoir footprints, as well as in planning to return salmon to the UCB.

Climate change projections in general provide information based on “climatic normals” or 30-year averages.  These provide useful data regarding general trends, but they do not capture the projected increases in extremes of temperature and precipitation which are often the main source of impacts to ecosystems and human infrastructure.  Across B.C. we have had some recent examples to demonstrate those phenomena, such as the 2021 heat wave and atmospheric river.  Here in the UCB, examples include the ongoing 2023 province-wide drought conditions contributing to very low levels on Arrow Lakes Reservoir; the 2012 wet spring associated with the Johnsons Landing landslides and flooding in the Kootenay system; and the 2013 Calgary storm that resulted in extreme flooding of rivers in both the East and West Kootenays.

The river management modelling team working to support the Canadian Columbia River Treaty negotiation delegation in its efforts to modernize the Treaty with the U.S., to better plan for the future, has incorporated two potential climate change inflow data sets into their modelling program.  These inflows are being used to assess the resilience of any proposed changes to reservoir management under possible climate change futures, including effects on seasonal reservoir elevation patterns and potential flooding in Canada and the U.S.  Projected changes in flow patterns (e.g. water flowing in and out of the reservoirs) are also accompanied by society’s changing patterns of electricity usage, including both overall increases in demand and seasonal shifts from heating to cooling, offering further complexity to water management decisions.

The changing conditions provide a challenging environment for future hydroelectric system managers, and the spectre of projected increases in frequency and intensity of extreme events will compound this complexity.  Associated increases in uncertainty will lead to a need for increased coordination and flexibility in future management decisions.  Development of an active adaptive management regime will be essential for moving forward in a resilient manner.