Regression Analysis of Normalized Difference Vegetation Index (NDVI) to Compare Seasonal Patterns and 15 Year Trend of Vegetation from East to West of Nepal

Understanding the changing patterns and trend of vegetation is essential for its socio-environmental values. Normalized difference vegetation index (NDVI), a satellite based data obtained from Moderate Resolutions Imaging Spectro-radiometer (MODIS) were analysed. The data have a characteristic resolution of 250 × 250 m2 and a 16-day composite period. They were ordered separately for each sample plot from east, centre and west of Nepal, for 15 years period, 2000 to 2015. MODIS, Land Surface Temperature (LST) data were used to identify unreliable NDVI values and hence eliminated. Also, the unusually fluctuating NDVI values during the rainy season were removed. A cubic spline function (for seasonal patterns), linear regression model (for NDVI trend) and generalized estimating equations (GEE for comparison of the changing trends) were the models used. The results showed a patterned annual seasonal vegetation and significant trends during the 15 years. Seasonal growth showed a peak in rainy season and trough in the winter season, with slight temporal variation among the areas with a characteristic shift of seasonal greening (start of greening) and browning (end of greening) from east to west of Nepal. The NDVI trend was significantly rising in eastern and western suburban areas while the central urban city had a significant decline. The temporal shift of start and end of the season from east to west can be of value to agriculturalists. INTRODUCTION The global climate has been changing and so is the trend of vegetation throughout the world. On one hand, vegetation is one of the prone factors to climate change while on the other hand, the vegetation helps to curb the effects of climate change effects. Moreover, changes in vegetation constantly help to change the climate factors at local or regional level (Meng et al. 2019, Zhu et al. 2016). Both increasing (Li et al. 2011, Liu et al. 2019) or decreasing patterns of vegetation have been observed in Asia. Apart from being geo giants of Asia, China and India represent as ‘greening leaders’ (Dunne 2019). Nepal, a small landlocked country between China and India, owns agriculture and forest as a major national economic resource and essentially needs to be aware of the changing trends of vegetation in the country. The climate-changing factors, for instance, temperature and rainfall are mostly correlated with vegetation (Liu 2017, Anbazhagan & Paramasivam 2016, Kaufmann et al 2003). The changes in terrestrial vegetation can modify regional and global climate at diurnal, seasonal and long term (Bounoua et al. 2000). The Australian Government Bureau of Meteorology (BoM 2014) suggests that the ability to link events in the natural world to a cycle that predicts seasonal changes is essential in the successful development of any community. These natural barometers are not uniform across the land but instead use the reaction of plants and animals to gauge what is happening in the environment. The cropping intensity (yield, the timing of plantation and harvest etc.) response to climate can help the understanding of proper growth, development and net production, which is practically influenced by previous year’s knowledge in most of the developing countries (Cooper et al. 1997). To understand the climate and seasonal effect to vegetation and crops, its start and end are required to appropriately fix the calendar of vegetation or other crops cycles. This start or end of crop seasons would change by time and space, the knowledge of which can eventually yield better. The spatio-temporal characteristics of remote sensing data are considered to be the primary advantage in environmental studies. MODIS is a sensor, fitted aboard the Terra and Aqua satellites by the National Aeronautics and Space Administration (NASA). It monitors environmental changes due to vegetation, temperature, droughts and flood on Earth 2021 pp. 267-273 Vol. 20 p-ISSN: 0972-6268 (Print copies up to 2016) No. 1 Nature Environment and Pollution Technology An International Quarterly Scientific Journal Original Research Paper e-ISSN: 2395-3454 Open Access Journal Nat. Env. & Poll. Tech. Website: www.neptjournal. com Received: 26-11-2019 Revised: 02-01-2020 Accepted: 01-03-2020