Growing-season trends in Fennoscandia 1982–2006, determined from satellite and phenology data

Abstract

The study area of Fennoscandia is a heterogeneous climatic region. To map the linear trends in onset, end, and length of the growing season in Fennoscandia, the bimonthly Global Inventory Modeling and Mapping Studies (GIMMS) normalized difference vegetation index (NDVI) satellite data set was used. The data set has an 8 8 km 2 spatial resolution and covers the period from 1982 to 2006. The mapping was done by applying pixel-specific threshold values to the NDVI data. These threshold values were determined from surface phenology data on birch Betula pubescens from 28 stations across the study area. During spring, most stations showed a moderately strong positive correlation between field and NDVI data. However, mapping of the end of the growing season showed less correlation with field phenology data and presented some uncertainty. On average, there was a linear trend for all of Fennoscandia of a 0.27 d yr -1 earlier onset of the growing season, a 0.37 d yr -1 later end of the growing season, and a 0.64 d yr -1 longer growing season. Within Fennoscandia, the trends showed similarities with vegetation zones and sections, which reflect the climatic gradients from north to south and from west to east in the study area. The southern and oceanic regions showed a trend of about a 1 d yr -1 longer growing season, in contrast to the alpine and northern continental regions which showed either no trend or a slightly shorter growing season.