ANALYSIS OF LONG-TERM EVI FOR VARIATIONS IN THE PHENOLOGICAL TRENDS OF MAJOR VEGETATION TYPES IN WESTERN HIMALAYA

摘要

Over the past few years, extreme weather events due to global climate change and anthropogenic pressure are among the main drivers of changing vegetation cover and productivity in western Himalaya. Changes in vegetation cover, their life-cycle events and how they are influenced by climatic variations is studied by phenological trends. In a region where field-based study is challenging due to high altitude and heterogenous relief, quantifying changes in vegetation photosynthetic activity using remote sensing can provide crucial information regarding variations in vegetation cover and its linkages with climate change and anthropogenic impacts. We conducted this study to detect variations in phenological trends over Uttarakhand Himalaya using MODIS EVI time-series data (2000-2014) and examined temporal patterns in five different vegetation types over different locations. To classify vegetation cover of Uttarakhand in different forest types, we used Vegetation Cover and Land Use map of Uttarakhand. Random points were generated in these forest types and EVI values were extracted from all the layers of our stacked MODIS data. In total most of the vegetation types showed an overall negative trend in mean EVI (browning) with time and are in agreement with previous studies that report only increasing brownness detected at broader scale using much coarser spatial resolution time-series. Sal mixed moist deciduous, in particular, showed a little more negative trend at all the locations as compared to others. Negative EVI trend (browning) in this region could possibly be attributed to the fire activities and land use change at forest fringe as well as temperature induced drought stress and cooling spring temperatures. Wet grassland, on the other hand, showed a positive trend in EVI (greening) which could be attributed to climate warming and wetting at higher altitude. Climate change could result in a replacement of high quality forest with low-quality forests, which are likely to lead to a significant biodiversity loss. An interplay between anthropogenic and climatic factors was also possible to affect the regional phenology.