Rapid retreat of permafrost coastline observed with aerial drone photogrammetry

Permafrost landscapes are changing around the Arctic in response to climate warming, with coastal erosion being one of the most prominent and hazardous features. Using drone platforms, satellite images and historic aerial photos, we observed the rapid retreat of a permafrost coastline on Qikiqtaruk–Herschel Island, Yukon Territory, in the Canadian Beaufort Sea. Erosion of this coast increasingly threatens the settlement located on the Kuvluraq–Simpson Point gravel spit. This spit accommodates several culturally significant sites and is the logistical base for the Qikiqtaruk–Herschel Island Territorial Park operations. The objectives of this study were to demonstrate the effective use of low-cost lightweight drones for: (i) assessing short-term coastal erosion dynamics over fine temporal resolution, (ii) evaluating short-term change detection in the context of long-term observations of shoreline change, and (iii) demonstrating the potential of these measurement tools for park management and decision makers. Using drones, we resurveyed a 500 m permafrost coastal reach at high temporal frequency (seven surveys over 40 days in 2017). The observed intra-seasonal shoreline changes were related to meteorological and oceanographic variables to understand intra-seasonal erosion dynamics. To put our short-term observations into historical context, we integrated analysis of shoreline positions in 2016 and 2017 with historical observations from 1952, 1970, 2000, and 2011. We found drone surveys analysed with image-based modelling yield fine-grain and accurately geolocated observations that are highly suitable to observe intra-seasonal erosion dynamics. In 2017, we observed coastal retreat of 14.5 m a⁻¹, more than six times faster than the long-term average rate of 2.2 ± 0.2 m a⁻¹ (1952–2017). Over a single 4 day period, coastline retreat exceeded 1 ± 0.1 m d⁻¹. Our findings highlight the episodic nature of shoreline change, which is poorly understood along permafrost coastlines. We conclude that the data available from drones is an effective tool to understand better the mechanistic short-term controls on coastal erosion dynamics and thus long-term coastline change, and has strong potential to support local management decisions regarding coastal settlements in rapidly changing Arctic landscapes.