Changes in surface water dynamics across northwestern Canada are influenced by wildfire and permafrost thaw

Abstract

The abundance and distribution of surface water at high latitudes is shifting rapidly in response to both climate change and permafrost thaw. In particular, the expansion and drainage of lakes is widespread but spatially variable, and more research is needed to understand factors driving these processes. In this study we used medium resolution (30m) remote sensing data to analyze changes in lake area in lowlands across permafrost regions of northwestern Canada. First, we used the Global Surface Water Dataset developed by the GLAD research group to map the absolute area of different land-water transitions across a 1.4 million km2 study domain. Next, we selected six regional study areas representing a range of climatic, geologic and hydrologic conditions. Within these regional study areas, we used the Landsat archive to map annual trends in the area of 27,755 lakes between 1985 and 2020. We trained a Random Forests model to classify lakes exhibiting significant increasing or decreasing trends in area, and assessed the relative importance of climate, disturbance and environmental variables in determining the direction of change. Our analysis shows that significant increases in lake area were more 5.6 times more frequent than decreases during the study period. Wildfire and ground ice content were the most important predictors of the direction of change. Greater ground ice content was associated with regions that experienced increases in lake area, while wildfire was associated with regions that experienced decreases in lake area. The effects of climate, including trends in mean annual temperature and total annual precipitation were smaller than disturbance and environmental factors, indicating that climate has likely had indirect effects on lake area changes over our period of study.