An analysis of 100 years of post-fire streamflow responses of British Columbia watersheds

Wildfires are becoming larger and more severe due to climate change. This trend is destructive to the forest ecosystem, disrupting many eco-hydrologic processes in forested watersheds. Effects can include rapid runoff responses, increased surface runoff, and elevated erosion, leading to lower water quality and long-lasting effects on hydrologic ecosystem services (such as flood regulation). However, post-fire hydrology studies often have variable and contrasting results, making cross-study comparisons difficult. Studies are typically short-term and focused on single wildfire events. This research aims to determine accurate indicators for post-fire flow responses. The study area includes 257 drainage basins (grouped into five ecozones) in British Columbia, Canada, known for its susceptibility to wildfires and floods. The study analyzes wildfire data from 1910 to 2020. Post-fire percent changes for four hydrological metrics (low, high, peak flows and runoff ratio) were calculated using pre-fire and post-fire values for multiple temporal bands. Using streamflow, precipitation, temperature, wildfire perimeters, and topographic data, statistical analyses including hypothesis testing and multiple linear regression were done. The two-sample Kolmogorov-Smirnov test results comparing the fire group against the two control groups resulted in highly variable p-values. Multiple linear regression was done to predict the percent changes for all flows. Regression yielded poor model performance, suggesting that the hydrometeorological parameters alone cannot explain the post-fire changes observed. The most frequently influential watershed indicators in post-fire streamflow responses were percent burn, maximum daily temperature, and elevation. Results across multiple temporal bands, ecozones and hydrological metrics over 100 years will aid future research on the wildfire effects on hydrology in forested watersheds.