Changes in greening in the High Arctic - insights from a 30-year AVHRR max NDVI dataset for Svalbard

Satellite-aided studies of vegetation cover, biomass and productivity are becoming increasingly important formonitoring the effects of a changing climate on the biosphere. With their large spatial coverage and good temporal resolution, space-borne instruments are ideal to observe remote areas over extended time periods.However, long time series datasets with global coverage have inmany cases too lowspatial resolution for sparsely vegetated high latitude areas. This study hasmade use of a newly developed 30 year 1 km spatial resolution dataset from1986 to 2015, provided by theNOAAAVHRR series of satellites, in order to calculate the annualmaximumNDVI over parts of Svalbard (78°N). This parameter is indicative of vegetation productivity and has therefore enabled us to study long-term changes in greeningwithin the Inner Fjord Zone on Svalbard. In addition, localmeteorological data are available to linkmaximumNDVI values to the temporal behavior of themean growing season (summer) temperature for the study area.Over the 30 year period,we find positive trends in bothmaximum NDVI (average increase of 29%) and mean summer temperature (59%),which were significantly positively correlated with each other. This suggests a temporal greening trendmediated by summer warming. However, as also recently reported for lower latitudes, the strength of the year-to-year correlation between maximumNDVI andmean summer temperature decreased, suggesting that the response of vegetation to summerwarming has not remained the same over the entire study period