Challenges in detecting high-arctic shrub expansion from optical remote sensing: implications for albedo and climate forcing

Domine, F., Belke-Brea, M., Bayle, A., Picard, G., Lévesque, E. et Kinnard, C. (2025). Challenges in detecting high-arctic shrub expansion from optical remote sensing: implications for albedo and climate forcing. Journal of Geophysical Research: Biogeosciences, 130 (10). Article e2024JG008593. ISSN 2169-8953 2169-8961 DOI 10.1029/2024JG008593

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Résumé

Abstract

Climate change-induced shrub expansion in the Arctic feeds back on climate by reducing surface albedo. Vegetation dynamics are typically monitored by tracking the evolution of vegetation indices, such as normalized difference vegetation index (NDVI), derived from satellite imagery in processes known as greening or browning. However, detecting changes in vegetation type requires sufficient spectral variation. Here, we measured the spectral albedos (346–2,400 nm) of assemblages of prostrate vegetation and of the only erect shrub species Salix richardsonii on Bylot Island in the eastern Canadian high-Arctic to assess spectral differences among common vegetation types. The broadband albedo of S. richardsonii (0.132 ± 0.009) was lower than that of prostrate vegetation (0.166 ± 0.008). However, NDVI values showed no significant difference (0.598 ± 0.074 vs. 0.561 ± 0.021). Satellite remote sensing using NDVI with spatial resolutions from 0.5 to 30 m using Pléiades, Sentinel-2 and Landsat-8 failed to detect differences in reflectance and NDVI between prostrate vegetation and S. richardsonii. These findings suggest that long-term NDVI trend analysis may be insufficient to capture the structural vegetation shift in these climate-sensitive areas. Failure to detect erect shrub expansion in the high-Arctic may therefore omit a climate change effect which produces a surface albedo decrease of 0.03 and a local summer solar forcing of 5.8 W m−2.

Plain Language Summary
With climate change, taller shrubs are replacing tundra vegetation in the Arctic. Shrubs reflect less sunlight than tundra vegetation: they have a lower albedo. Shrub expansion thus contributes to further warming, creating positive feedback on climate, which must be measured to improve climate models. Shrub expansion across the Arctic is usually monitored using satellite remote sensing in the visible and infrared ranges. Because satellites only monitor a limited number of wavelengths, indices combining several wavelengths are used to track vegetation changes. The most commonly used index is called Normalized difference vegetation index (NDVI). Here we use both field measurements, which allow shrub detection with certainty, and satellite data to test whether satellites can accurately detect shrub expansion in the high-Arctic. We show that, in the field, shrubs have NDVI values similar to low vegetation. NDVI from satellite also fails to distinguish shrubs from low vegetation. However, our field measurements show that shrubs in the high-Arctic have an albedo of 0.132, compared to 0.166 for low vegetation. This difference creates a local surface forcing of 5.8 W m−2. In comparison, the global forcing due to anthropogenic CO2 is about 2.3 W m−2. Common shrub detection methods in the high-Arctic therefore miss an important local climate forcing.

Type de document:	Article
Date de dépôt:	30 juill. 2026 16:00
Dernière modification:	30 juill. 2026 16:00
Version du document déposé:	Version officielle de l'éditeur
URI:	https://depot-e.uqtr.ca/id/eprint/13104

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