Spatially variable vegetation greenness trends in Uttarakhand Himalayas in response to environmental drivers

Abstract

Over the last few decades, Western Himalayas experienced high population growth and increase in exploitative land use practices. This trend coupled with influence of climatic variability has resulted in significant negative effects on vegetation cover and productivity. This study aims to understand the spatial patterns and severity of these impacts in Uttarakhand Himalayas. Specifically, the objectives of this study are twofold: first, to quantify interannual trends in vegetation greenness by conducting nonparametric Mann-Kendall trend analysis on MODIS-NDVI time series (2000-2014) and, second, to assess distribution of this trend with respect to land use land cover properties and elevation zones. The results show that out of the total vegetated area in Uttarakhand, 2,686.95 km2 (5.69%) showed changes in the vegetation greenness and 73.64% of this change was significant negative trend (browning). While areas with <800 m elevation showed dominant browning, those between 800 and 1600 m showed significant positive trend (greening), and majority of areas >1600 m were characterized by browning trend. Majority of intensively cultivated irrigated croplands in the Himalayan foothills and areas around growing urban centers showed widespread browning, whereas areas of rainfed cultivation showed dominant greening. Browning was also dominant in closed needle leaf forests and alpine shrublands, except areas where human impacts has led to more mixed patterns. These results highlight previously unreported fine-scale spatial variations in vegetation productivity trend with respect to both elevation and LULC properties.