ABSTRACT
The variations in the climate forcing, natural hazards, and human-induced land use/land cover (LULC) changes have significantly influenced ecosystems all around the globe. Mountain ecosystems such as the Himalayas are particularly vulnerable to the changing climate. This study attempts to unravel the impact of climate forcing on the photosynthetic variability in different relief zones in the Himalayan terrain in the peak monsoon season from June to September (JJAS) over the last two decades (2000-2019). The spatio-temporal distribution and the trend in normalized difference vegetation index (NDVI) (based on MODIS product), precipitation (GPM product), and air temperature (GLDAS product) were analyzed using long-term datasets from 2000 to 2019. The maximum NDVI was seen in Eastern Himalaya at 0.879, Central Himalaya at 0.83, and Western Himalaya at 0.77. The vigorous vegetation is predominantly found in the lower relief zone (< 2600m) across several parts of the Himalaya. However, the maximum NDVI (> 0.6) was observed in the relief zone of 1,300-2,600m. The Eastern Himalaya was the wettest, with mean precipitation intensity of 3.25-20.5mm/day and Central Himalaya at 2.5-17.6 mm/day, whereas the Western Himalaya was the driest at 0.1-12.8mm/day. Increasing (i.e., greening) as well as decreasing (i.e., browning) vegetation trends as estimated using NDVI were found across the Himalaya. The majority of the Eastern Himalaya (63.37%) exhibited browning trends due to anthropogenic intrusions causing LULC changes and to natural hazards, such as fires and landslides below 2,600m. Therefore, proper monitoring of vegetation along with planning and conservation are required to prevent these vulnerable ecosystems from changing climate.
