In the prairie basins around the St. Mary-Milk Rivers and the Souris River, climate models are projecting hotter, more extreme weather in coming decades. In a region of the continent known for swinging between dry and wet periods, officials are already looking at adapting their current procedures to prepare.
Over the past 100 years of operation, the IJC’s Accredited Officers for the St. Mary-Milk Rivers have seen a wide range of climate variability, said Canadian field representative Jeff Woodward, also manager of the hydrometric program for the prairies with Environment and Climate Change Canada (ECCC). As a result, existing practices are designed around managing “big swings” in the volume of water available for irrigation, residents and wildlife.
And those practices may become more relevant in years to come. Woodward said the Accredited Officers are expecting temperatures to climb 2-3 degrees C (3.6-5.4 degrees F), but climate models don’t have enough information to determine if the area will become wetter or drier in the future. Regardless of which outcome plays out, the board expects dry periods to become drier and wet periods to become wetter, with each period potentially lasting longer.
John Kilpatrick, US field representative for the Accredited Officers and director of the US Geological Survey (USGS) Wyoming-Montana Water Science Center, said current conditions aren’t outside the historical range, but they’re creeping near the edges. The US Bureau of Reclamation has started a modeling project of potential climate change impacts on future irrigation.
The St. Mary and Milk Rivers follow a seasonal pattern where snowmelt and spring storms provide the bulk of the water runoff for the year. The Accredited Officers apportion natural streamflows to try to ensure everyone gets their share under the Boundary Waters Treaty, which intended for Canada and the United States to each receive half the combined flow of these streams. Both countries have storage reservoirs that fill during spring freshet (runoff) and are used during the irrigation season.
The Accredited Officers may need to take action if they find that the timing of the irrigation period changes, Kilpatrick said. The board’s job may become more difficult if the spring runoff amount is reduced and/or occurs earlier in the year. This could result in extended dry periods and insufficient water being held in reservoirs to meet the needs of irrigation-reliant farmers and ranchers. A wet future would be easier to deal with than the alternative, Woodward added, since there are no major communities along either river facing flood risks and the reservoirs could be used to retain the additional water.
In the Souris basin, Woodward – who also serves on the International Souris River Board - said floods and in particular droughts have been behind the development of existing apportionment and irrigation methods, which has made the process somewhat resilient to climate change.
“Over the past four or five years, there has been a noticeable change in the timing of the water in this basin,” Woodward said. He explained that water management in the Souris basin is focused on water coming in during the early spring freshet, but in recent years more significant amounts of water have come in from late spring and summer storms. At this point, he added, the board hasn’t been able to determine if this is just natural variability or because of climate change.
Woodward said there has been numerical modeling by the USGS in the Souris River basin to develop potential future climate change scenarios. Since the two basins are similar in climate and how they get their water, he believes there is room to develop adaptive measures for both areas. The model, built using recorded weather data and tree-ring analyses as a baseline, found that the region tends to alternate on a multi-decadal timescale between dry and wet climates, with the last such change taking place around 1970.
The model was used to determine the likelihood of another major flood along the Souris River, similar to the devastating one in 2011, and found that there is an annual 2 percent chance of another major flood during the current wet cycle, with no prediction on how long this cycle will last before returning to a dry one.
Bruce Davison, a hydrologist with ECCC, is working on a proposal to use computer models to get a better idea of what extreme climate change scenarios – and situations in-between – could mean for the basin. This way, the board could get a better understanding of how climate change could impact its activities.
“I’ve been participating in (the IJC’s) climate change working group meetings, and my understanding is that (this) group wants to provide a bit of a framework for boards to work with when thinking about climate change, and how it may impact the activities of (that particular) board,” Davison said.
While the basins are managed in a drought-resistant way, if climate change pushes the extremes of wet and dry periods, water managers may have some trouble making sure there’s enough water to go around.