Bio-climatic factors drive spectral vegetation changes in Greenland

Abstract. The terrestrial Greenland ecosystem (ice-free area) has undergone significant changes over the past decades, affecting biodiversity. Changes in air-temperature and precipitation have modified the duration and conditions of snowpack during the cold season, altering ecosystem interactions and functioning. In this study, we statistically aggregated the Copernicus Arctic regional reanalysis (CARRA) and remotely-sensed spectral vegetation data from 1991 to 2023 by using principal component analysis (PCA), in order to I. examine key sub-surface and above-surface bio-climatic factors influencing ecological and phenological processes preceding and during the thermal growing season in tundra ecosystems; II. interpret spatio-temporal interactions among bio-climatic factors on vegetation across Greenland; III. investigate bio-climatic changes dependent on location and elevation in Greenland; IV. identify regions of ongoing changes in vegetation distribution.

Consistent with other studies, PCA effectively clustered bio-climatic indicators that co-vary with summer spectral vegetation, demonstrating the potential of CARRA for biogeographic studies. The duration of the thermal growing season (GrowDays) emerged as the pivotal factor across all ecoregions (with increases up to 10 days per decade), interacting with other bio-climatic indicators to promote vegetation growth. Regions with significant snow height decrease occur along with an earlier snowmelt period (up to 20 days per decade), which triggers the onset of GrowDays earlier. In most regions, we find that shallower snowpacks tend to melt slower. We hypothesise that slow snowmelt rates foster microbial activity, enriching the soil with nutrients. The combined effect of soil nutrients and the resulting warming in spring (up to 1.5 ºC per decade), promotes early plant development. These bio-climatic changes, in the cold and summer season, have led to northward and upward vegetation expansion. The distribution of vegetation has expanded in Northeast Greenland by 22.5 % increase with respect to 2008–2023, leading to new vegetated areas. We report little to no change in the length and onset of the GrowDays along the coast in Northeast Greenland, in contrast with more pronounced changes inland and at higher elevations, hence showing an elevation-dependent response (increases up to 5 days per decade per km elevation). Our study determines a set of bio-climatic indicators relevant for understanding vegetation. These insights provide a basis to validate bio-climatic indicators from climate models to assess future vegetation changes across Greenland under a changing climate.