Normalized Difference Vegetation Index (NDVI) Change Map between 9/22/2024 and 10/12/2024, Southern Appalachian Mountains (ver. 1.1, March 2025)

The Normalized Difference Vegetation Index (NDVI) Change Map (Helene_LS_Sentinel2_NDVI-change_20241012-20240922.tif) can be used to identify areas in the southern Appalachian Mountains where vegetation was removed or damaged due to landslides, debris flows, flooding, and wind damage by Hurricane Helene and the heavy rainfall that preceded it. The map was generated using the Red and Near Infrared (NIR) spectral bands from Sentinel-2 L2A data collected on 9/22/2024 (pre-event) and 10/12/2024 (post-event). NDVI is an index that indicates the greenness and density of vegetation. We calculated NDVI for the pre- and post-event data individually, using the following formula: (NIR - Red) / (NIR + Red). The NDVI change map here was then derived by subtracting the pre-event NDVI from the post-event NDVI. Negative values on the NDVI change map highlight areas where vegetation was present pre-event and has subsequently been removed or damaged post-event.