Trends and drivers of Arctic lake color change from Landsat time series

• Declining red and green surface reflectance in western Canadian Arctic lakes. • Abrupt changes in lake color and NDTI associated with slumping and wildfire. • Lake color change follows warm summer temperature with a 2-year lag. • Tailored cross-sensor calibration of Landsat essential for Arctic lake studies. Arctic lake color and quality are changing in response to the warming climate, permafrost degradation, and intensifying disturbances. These changes have important implications on carbon and nutrient cycling, wildlife habitat, and water resources planning. However, the drivers, spatial distribution, and long-term trajectories of these changes remain poorly characterized on regional scales (∼100 km). In this study, we examined over 3,000 lakes in part of the Mackenzie Delta, Tuktoyaktuk Coastlands, and adjacent upland tundra in the Northwest Territories, Canada, to quantify both gradual and abrupt changes in lake color using harmonized Landsat time series from 1985 to 2022. Across the region, we found average declines of surface reflectance in the red and green bands by 13 % and 15 % over the last four decades, respectively. In comparison, the Normalized Difference Turbidity Index (NDTI) trends differed between sub-regions, with a decadal increase in the Tuktoyaktuk Coastlands and a decrease in the Mackenzie Delta. We identified a positive, lagged correlation between abrupt lake color change and mean summer air temperature (MSAT), particularly in the Tuktoyaktuk Coastlands (R = 0.7, lag = 2 years), indicating a delayed impact of warm summers on lake color. One important mechanism of such impact was lakeshore thaw slumping intensified by rising summer temperatures, with slump-affected lakes experiencing abrupt increases in surface reflectance and NDTI driven by sediment input. We identified fire as another important driver of lake color dynamics, which led to greater changes in lake surface reflectance (p < 0.01) and NDTI (p = 0.1) compared to surrounding lakes. These findings demonstrate the value of harmonized Landsat time series for characterizing multifaceted Arctic lake color dynamics, along with their drivers and impacts.