Bio-climatic factors drive spectral vegetation changes in Greenland

Abstract. Terrestrial ecosystems (ice-free areas) in Greenland have undergone significant changes over the past decades, affecting biodiversity. Changes in near-surface air temperature and precipitation have modified the duration and conditions of snowpack during the cold season, altering ecosystem interactions and functioning. In our study, we statistically aggregated the Copernicus Arctic Regional Reanalysis (CARRA) and remotely sensed data on spectral vegetation, spanning from 1991 to 2023. We used principal component analysis (PCA) to examine key subsurface and above surface bio-climatic factors influencing ecological and phenological processes, both preceding and during the thermal growing season in tundra ecosystems. Subsequently, we interpreted spatio-temporal interactions of bio-climatic factors with vegetation and investigated bio-climatic changes dependent on latitude and topographical features in Greenland. Ultimately, we described regions of ongoing changes in vegetation distribution. Our results indicate that, particularly in West Greenland, vegetation has responded strongly to prevailing weather patterns of past decades. The PCA effectively clustered bio-climatic indicators that co-vary with summer vegetation, demonstrating the potential of CARRA for use in biogeographic studies. Among the factors studied, the duration of the thermal growing season (GrowDays) was pivotal across all ecoregions, increasing by up to 10 thermal growing season days per decade. These increases, interacting with other bio-climatic indicators, further promoted summer vegetation growth. The earlier onset of GrowDays was driven by warming (up to 1.5 °C per decade), reduced winter precipitation, earlier snowmelt (on the order of 20 d per decade), and significant decreases in snow depth. We report that regions with shallower snowpacks melt more slowly during the ablation period and are linked with a higher soil water content in the spring season. This relation not only coincides with the greenest regions in West and Southwest Greenland, but also with regions where green vegetation has recently emerged. These processes occur prior to the onset of GrowDays and are later combined with summer weather conditions that favour warmer temperatures and clear skies, resulting in significant summer greening. From spatio-temporal increases in spectral vegetation, we infer vegetation expansion northward and towards the interior of Greenland. For instance, vegetation in Northeast Greenland has expanded by 22.5 %, leading to newly vegetated areas compared to the 1991–2007 period. While our statistical outcomes and interpretations derived from reanalysis and remote sensing data include uncertainties, they are corroborated by in situ studies conducted in the tundra region. Our study highlights the applicability of bio-climatic indicators from climate models as a foundational way to assess future changes in vegetation while also demonstrating the need to include such indicators into permafrost dynamics schemes. If integrated, these bio-climatic indicators will improve our understanding of the atmosphere–vegetation–permafrost–carbon feedback loops across terrestrial Greenland with the changing climate, leading to better predictions of their responses.