Increased wetness confounds Landsat-derived NDVI trends in the central Alaska North Slope region, 1985–2011

• Published in: Environmental Research Letters
• Main Authors: Martha K Raynolds, Donald A Walker
• Format: Article in Journal/Newspaper
• Language: English
• Published: IOP Publishing 2016
• Subjects: arctic vegetation; brightness index; greenness index; wetness index; NDVI; Prudhoe Bay; Environmental technology. Sanitary engineering; TD1-1066; Environmental sciences; GE1-350; Science; Q; Physics; QC1-999; Arctic; Alaska North Slope; north slope; Alaska
• Online Access: https://doi.org/10.1088/1748-9326/11/8/085004; https://doaj.org/article/5d37b97423c041298dd512dd35426292

Satellite data from the circumpolar Arctic have shown increases in vegetation indices correlated to warming air temperatures (e.g. Bhatt et al 2013 Remote Sensing http://dx.doi.org/10.3390/rs5094229 5 http://dx.doi.org/10.3390/rs5094229 http://10.3390/rs5094229 ). However, more information is needed at finer scales to relate the satellite trends to vegetation changes on the ground. We examined changes using Landsat TM and ETM+ data between 1985 and 2011 in the central Alaska North Slope region, where the vegetation and landscapes are relatively well-known and mapped. We calculated trends in the normalized difference vegetation index (NDVI) and tasseled-cap transformation indices, and related them to high-resolution aerial photographs, ground studies, and vegetation maps. Significant, mostly negative, changes in NDVI occurred in 7.3% of the area, with greater change in aquatic and barren types. Large reflectance changes due to erosion, deposition and lake drainage were evident. Oil industry-related changes such as construction of artificial islands, roads, and gravel pads were also easily identified. Regional trends showed decreases in NDVI for most vegetation types, but increases in tasseled-cap greenness (56% of study area, greatest for vegetation types with high shrub cover) and tasseled-cap wetness (11% of area), consistent with documented degradation of polygon ice wedges, indicating that increasing cover of water may be masking increases in vegetation when summarized using the water-sensitive NDVI.