Sammendrag
The global temperature is increasing, and this is affecting the vegetation phenology in
many parts of the world. The most prominent changes occur at northern latitudes such as our
study area, which is Svalbard, located between 76◦300N and 80◦500N. A cloud-free time series of
MODIS-NDVI data was processed. The dataset was interpolated to daily data during the 2000–2020
period with a 231.65 m pixel resolution. The onset of vegetation growth was mapped with a NDVI
threshold method which corresponds well with a recent Sentinel-2 NDVI-based mapping of the onset
of vegetation growth, which was in turn validated by a network of in-situ phenological data from
time lapse cameras. The results show that the years 2000 and 2008 were extreme in terms of the late
onset of vegetation growth. The year 2020 had the earliest onset of vegetation growth on Svalbard
during the 21-year study. Each year since 2013 had an earlier or equally early timing in terms of the
onset of the growth season compared with the 2000–2020 average. A linear trend of 0.57 days per
year resulted in an earlier onset of growth of 12 days on average for the entire archipelago of Svalbard
in 2020 compared to 2000.
MODIS; NDVI; time series; onset of vegetation growth; trend; Arctic; Svalbard;
spatial scales
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