Detecting hotspots of ecosystem change with remote sensing across the Arctic

 

The Arctic region is warming faster than elsewhere on Earth, at a rate nearly twice the global average. This warming is expected to negatively impact vegetation, hydrology, terrain thaw, and many other ecosystem properties. Here we identify primary hotspots of landscape changes occurring across the Arctic using multiple observations from reanalysis and satellite remote sensing, spanning visible, near-infrared, and thermal infrared (VIS-NIR-TIR) and microwave bands. This suite of VIS-NIR-TIR and microwave-derived products allows for the longer-term monitoring of ecological indicators for climate (e.g., temperature and precipitation), landscape surface frozen status, ecosystem water stress, and vegetation. Specifically, we examined “hotspots” (i.e., Getis-Ord Gi* statistics) and associated rates of change in thermal state, including near-surface air temperature; annual start and length of the surface non-frozen period; soil thaw depth. To identify regional changes in wetness, we examined hotspots of change and trends in precipitation; snow cover; surface water inundation; soil moisture status. For vegetation, we examined VIS-NIR greenness indices; annual start date and length of growing season; history of disturbance (i.e., fires). Lastly, we examined higher (30 m) resolution Landsat and Sentinel 2 imagery and in situ observations to better understand the drivers of change and the potential impacts to local communities and infrastructure. Our hotspot analysis indicated the most severe changes occurring in the Russian Far East, the Northwest Territories of Canada, and portions of Alaska including the North Slope.  Specifically, the Northwest Territories have experienced warming, greening and wetting while the Russian Far East has experienced large temperature increases, an increase in permafrost active layer thickness, and a potential lengthening of the non-frozen season (as indicated by the classification of the ground surface state by microwave remote sensing). The North Slope of Alaska has experienced increasing temperatures, precipitation and a decrease in the number of frozen days per year. Information obtained through this remote sensing analysis, integrated into a geographic information system, can be used to better support decision making for land management and risk assessments across the rapidly warming Arctic-boreal region.