Wildfire increased summer low flows in snow-dominated watersheds: A combined approach of hydrometric monitoring and geochemical tracing

Forests are experiencing more frequent and intense wildfires in Canada, which pose considerable threats to water quantity and quality, particularly during the summer low-flow period when water demand is high. While the impacts of wildfire on hydrology have been widely assessed at the watershed scale, the underlying mechanisms of the responses of summer low flows remain poorly understood. In this study, we employed an integrated research framework that combines hydrometric monitoring with geochemical tracing to evaluate how the 2021 White Rock Lake Wildfire affected summer low flows, and to identify the underlying mechanisms governing these responses in the Okanagan Valley, British Columbia (BC), Canada. We found that (1) summer low flows, represented by Q 90 (flows exceeded at 90% of the time in summer) significantly increased following the wildfire ( p ​< ​0.05); (2) summer low flows were primarily regulated by snow water in early summer (July), while dominated by groundwater in late summer (August and September); and (3) enhanced snow water contribution and reduced evapotranspiration (ET) were two primary contributors to the increased summer low flows. Our results provide insights for developing sustainable water management strategies for the region in the context of climate change and increasing forest disturbance. This study also demonstrates that the combination of hydrometric monitoring and geochemical tracing is an effective approach towards uncovering mechanisms that drive low-flow responses. • Hydrometric monitoring and geochemical tracing was used to investigate summer low-flow responses and the mechanisms. • Wildfire significantly increased summer low flows (Q 90 ). • Snow water primarily supplied early-summer low flows, while groundwater dominated the late summer low flows. • Enhanced snow water contribution and reduced evapotranspiration were two drivers of enhanced post-fire summer low flows.