Landsat-based multi-decadal spatio-temporal assessment of the vegetation greening and browning trend in the Eastern Indian Himalayan Region

Abstract

The Eastern Indian Himalayan region (EIHR) is biodiversity-rich and ecologically sensitive. The region is under tremendous pressure due to a variety of challenges such as population pressure, shifting cultivation, and climate change leading to impact the vegetation. Therefore, the present study focuses on the evaluation of spatio-temporal dynamics of vegetation utilizing the trend and rate of change of annual median NDVI (Normalized Difference Vegetation Index) of EIHR. The annual median NDVI composite of EIHR was prepared for each year from 1990 to 2019 using Landsat satellite data collection available for the entire year in Google Earth Engine (GEE). The time series annual median NDVI data were analysed for the non-parametric (Mann-Kendall and Theil-Sen) trend analysis. Based on these trends, regions of greening (increasing NDVI) and browning (decreasing NDVI) was assessed. It revealed that the majority of the EIHR has a more greening trend than browning with an annual rate of increase of NDVI between 0.002 and 0.007 with a very high (p<0.01) to high (p<0.05) level of confidence. Further, the NDVI trend was also analysed for its spatial distribution in forest type and forest cover of EIHR. It was found that while about 58% of the total forest area has shown a continuously increasing NDVI trend, only less than 1% area has a decreasing trend. The increase in the forest area and greening trends in NDVI may be attributed to the conservation efforts. The outcome of the study may help in the better management of forest ecosystems besides the future planning for landscape and regional development.