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

Abstract

Satellite-aided studies ofvegetation cover, biomass and productivity are becoming increasingly important for monitoring the effects ofa 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 seriesdatasets with global coverage have in many cases too lowspatial resolution for sparsely vegetated high latitude areas. Thisstudy has made use ofa newly developed 30 year 1 kmspatial resolution dataset from 1986 to 2015, provided bythe NOAAAVHRR series ofsatellites, in order to calculate the annual maximum NDVI over parts of Svalbard ( 78 ° N ) .This parameterisindicative ofvegetation productivity and has therefore enabled usto study long-term changes in greeningwithin the Inner Fjord Zone on Svalbard. In addition, local meteorological data are availabletolinkmaximumNDVIvaluesto the temporalbehaviorofthe meangrowingseason ( summer ) temperature for the study area. Overthe 30 yearperiod, we fi nd positive trends in both maximum NDVI ( average increase of29% ) and mean summer temperature ( 59% ) , which were signi fi cantly positively correlated with each other.Thissuggests a temporal greening trend mediated by summer warming. However, as also recently reported for lower latitudes, the strength ofthe year-to-year correlation between maximum NDVI and mean summer temperature decreased, suggestingthatthe response of vegetationto summer warming has not remainedthe same overthe entire study period.