Understanding and Assessing Impacts
Okanagan river flow and mainstem lake levels are regulated by dams and other structures known as the Okanagan Lake Regulation System (OLRS). Lake management is challenging due to natural variability between wet and dry seasons, balancing lake outflows with ecosystem health, and using inflow forecasts that have uncertainty and are vulnerable to extreme weather events. The impacts of climate change are also posing new challenges for lake management. The worst flood and highest lake levels were recorded in 2017 following an atypical freshet driven by late season snow accumulation, heavy rain, and rapid snow melt and the worst drought and lowest lake levels were recorded in 2021. The OLRS is near the end of its lifespan, and it is important an updated system reflects societal priorities, respects Indigenous rights and title, and considers future climate change scenarios. To determine how climate change will impact lake levels and the existing regulation system, information from the 2020 OBWB Floodplain Mapping Report conducted by Northwest Hydraulic Consultants Ltd. (NHC) was utilized. The Floodplain Mapping Report used ECCC’s CanLEADV1 50-climate ensemble dataset for RCP 8.5 to analyze future climatic changes in the Okanagan Basin. The ensemble dataset was downscaled and used to drive a hydrologic model of the Okanagan River Basin from 1950 to 2100. The hydrologic model was calibrated to either standard lake regulation for current operating rules or future regulation which accounted for how climate change would alter basin hydrology. Based on the model results, while historically the 2017 event seems rare and extreme it becomes more common in the future. Furthermore, when considering lake regulation, maintaining standard regulation in the future could result in more consistent and extremely high lake levels compared to a future regulation system which would keep the Okanagan Lake below 2017 levels most of the time.