Future Water Supply and Demand in the Okanagan Basin, British Columbia: A Scenario-Based Analysis of Multiple, Interacting Stressors

Surface water is critical for meeting water needs in British Columbia’s Okanagan Basin, but the timing and magnitude of its availability is being altered through climate and land use changes and growing water demand. Greater attention needs to be given to the multiple, interacting factors occurring and projected to occur in this region if water is going to be sustainably provisioned to human users and available for ecosystem needs. This study contributes to that goal by integrating information on physical, biological and social processes in order to project a range of possible changes to surface water availability resulting from land-use, climatic and demographic change, as well as from Mountain Pine Beetle infestation. An integrated water management model (Water Evaluation and Planning system, WEAP) was used to consider future scenarios for water supply and demand in both unregulated and reservoir-supported streams that supply the District of Peachland. Results demonstrate that anticipated future climate conditions will critically reduce streamflow relative to projected uses (societal demand and ecological flow requirements). The surficial storage systems currently in place were found unable to meet municipal and instream flow needs during “normal” precipitation years by the 2050s. Improvements may be found through demand reduction, especially in the near term. Beyond the implications for the District of Peachland, this work demonstrates a method of using an accessible modeling tool for integrating knowledge from the fields of climate science, forest hydrology, water systems management and stream ecology to aid in water and land management decision-making.