Fluvial response to climate change-induced stream capture, Yukon, Canada

Abstract:

In May 2016, glacier runoff diverted from Ä’äy Chù (Slims River) to Kaskawulsh River in southwest Yukon, in response to glacier retreat. Such a dramatic shift has rarely been observed in real time and thus knowledge of short-term fluvial response is limited to analogous examples such as dam decommissioning’s. We investigated the geomorphic responses of both rivers to these changes in discharge by quantifying braiding intensity pre- and post- diversion using satellite imagery from Planet Labs, SPOT, and Sentinel satellites. We find that the braiding intensity of Kaskawulsh River nearly doubled between 2015 and 2016, the same time period, the braiding intensity of Ä’äy Chù decreased by about half as the river carried less flow. Since 2016, braiding intensity has remained high in the Kaskawulsh River, and low in Ä’äy Chù. Precipitation and air temperature data from nearby stations do not show trends thought to directly influence the changes in braiding intensity during this time period. Quantifying braiding intensity of each river before and after the 2016 diversion illustrates their rapid geomorphic response to this nearly geologically instantaneous event.