Non-linear response of vegetation to coherent warming over northern high latitudes

Abstract

This study evaluates the large-scale changes in vegetation greenness at northern high latitudes (>60？N) using satellite-measured normalized difference vegetation index (NDVI) and station-merged temperature, precipitation and soil moisture for the period 1982？2008. During this 27-year period, although coherent warming trends were observed at most of the high latitudes, changes in the NDVI showed apparent spatial and temporal heterogeneity. In particular, changes in the hemi- spheric mean NDVI increased until 1997, but decreased thereafter. Maximum covariance analysis, which is a statistical method to detect large-scale covariability between two variables over time, reveals significant relationships between NDVI and soil moisture (and/or precipitation) in the regions of negative NDVI trends. These results further suggest that local moisture availability also plays a consider- able role in the large-scale changes in vegetation as well as coherent warming over the northern high latitudes. moisture for the period 1982？2008. During this 27-year period, although coherent warming trends were observed at most of the high latitudes, changes in the NDVI showed apparent spatial and temporal heterogeneity. In particular, changes in the hemi- spheric mean NDVI increased until 1997, but decreased thereafter. Maximum covariance analysis, which is a statistical method to detect large-scale covariability between two variables over time, reveals significant relationships between NDVI and soil moisture (and/or precipitation) in the regions of negative NDVI trends. These results further suggest that local moisture availability also plays a consider- able role in the large-scale changes in vegetation as well as coherent warming over the northern high latitudes.