PHENOLOGICAL ANALYSIS OF THE WESTERN HIMALAYAN FOREST USING TEMPORAL REMOTE SENSING DATA

Abstract. The Himalayan range is considered to include the highest mountains on earth, with a widely recognized assortment of flora and fauna. The Indian Himalayan range spread over 10 states, of which being Uttarakhand, has the largest forest cover of 48.5% of the total area forest. In Doon Valley, the phenological behavior and variations of several forest types have been studied using the Normalized Difference Vegetation Index (NDVI) and Temporal Normalized Phenology Index (TNPI) along with elevation, surface temperature, slope, and aspect data into consideration. A two-scale method has been employed to study forest phenology, using Sentinel-2 data at 10 m spatial resolution for local-scale studies and MODIS NDVI data at 250 m spatial resolution to find large-scale phenological patterns. The framework used in this study is based on Google Earth Engine (GEE) which has potential applications at various spatial and temporal scales. Multiple phenological phases and phenological metrics have been identified and examined within the duration from December 2018 to May 2023. The investigation concluded that phenological behaviors were considerably affected by environmental and topographic variables such as elevation, surface temperature, slope, and aspect. Significant changes in phenology were recorded at low altitudes; however, less fluctuation was reported at medium to higher elevations due to remoteness at greater elevations. Using NDVI from open-source MODIS and Sentinel-2 datasets, TNPI has been successfully tested for this forest region. The findings showed that this study opens new opportunities for trend analysis of forest health and productivity.