Comment on hess-2020-613

Abstract

The cold interior of Western Canada, east of the Continental Divide, has one of the world's most extreme and variable climates and is experiencing rapid environmental change. In the large Mackenzie and Nelson River basins, the warming climate is changing the landscape, 15 vegetation, cryosphere, and hydrology. This is a study of a large number (395) of natural (unmanaged) gauged basins where streamflow may be continuous or temporary, and observed streamflow records had been collected either year-round or during only the warm season. Each station may have records for a different series of years between 1910 and 2012. Instead of a common period of years and a small number of stations, as in many trend studies, an annual 20 warm season time window where observations were available across all stations is used to classify [1] streamflow regime using dynamic time-warping, and [2] seasonal trend patterns with k-means clustering. The trends in seasonal streamflow patterns were compared to changes in satellite Normalized Difference Vegetation, Water, and Snow Indices (NDVI, NDWI, and NDSI) for each gauged basin using Landsat 5 TM imagery between 1985 and 2010. 25Twelve streamflow regime types were identified using dynamic time-warping which overcomes timing differences in streamflow generation due to latitude or elevation. These streamflow regime types exhibit a strong connection to location; the spatial distribution follows ecozones and shows a strong distinction between mountains and plains in the study area.Clustering of seasonal trends using the annual common time window resulted in six trend 30 patterns that also have a strong and distinct spatial organization. The trend patterns include one with decreasing streamflow, four with different patterns of increasing streamflow, and one with stations without trend structure. Trends in the mean, minimum, and maximum of three satellite indices were determined; the spatial patterns of trends in NDWI and NDSI were similar to each other, but different from NDVI trends. Streamflow regime types, the trend patterns, 35 and satellite indices trends each showed spatially coherent patterns reflecting the influence of sources in the Canadian Rockies and other range in the west and poorly defined drainage basins due to post-glacial topography in the east and north. The overlap between hydrological and satellite index trends were not consistent across the study area. Three particular areas of change were identified: [i] in the mountains or lake-dominated, cold taiga-covered subarctic, north of 40 60°N, streamflow and greenness were increasing while wetness and snowcover were decreasing, [ii] in the forested Boreal Plains, particularly in the mountain west, streamflows