Is Alaska’s Yukon–Kuskokwim Delta Greening or Browning? Resolving Mixed Signals of Tundra Vegetation Dynamics and Drivers in the Maritime Arctic

Abstract Alaska’s Yukon–Kuskokwim Delta (YKD) is among the Arctic’s warmest, most biologically productive regions, but regional decline of normalized difference vegetation index (NDVI) has been a striking feature spaceborne Advanced High Resolution Radiometer (AVHRR) observations since 1982. This contrast with “greening” prevalent elsewhere in low Arctic raises questions concerning climatic and biophysical drivers tundra productivity along maritime–continental gradients. We compared NDVI time series from AVHRR, Moderate Imaging Spectroradiometer (MODIS), Landsat for 2000–19 identified trend reference to sea ice climate datasets, ecosystem disturbance mapping, field measurements vegetation, knowledge exchange YKD elders. All showed increasing maximum NDVI; however, whereas MODIS trends were very similar, AVHRR-observed weaker had dissimilar spatial patterns. The AVHRR records time-integrated dramatically different; indicated weak declines, strong increases throughout YKD. Disagreement largely arose during shoulder seasons, when there partial snow cover high cloud frequency. Nonetheless, both shared correlations spring extent summer warmth. Multiple lines evidence indicate that, despite frequent disturbances interannual variability warmth, on Although similar more continental parts Arctic, our intercomparison highlights sources uncertainty maritime areas like that currently, or soon will, challenge historical concepts “what Arctic.”