Spatio-temporal variability of vegetation and its relation to different hydroclimatic factors in Bangladesh

Bangladesh boasts some of the most diverse ecosystems on Earth, where vegetation plays a crucial role in maintaining ecological equilibrium and environmental sustainability. However, human activities and the impacts of global warming are taking a toll on vegetation, leading to a decline in green cover within urban areas and subsequent temperature rise. The intricate relationships between precipitation, temperature, evapotranspiration, and vegetation dynamics are of paramount importance. In this study, we investigate the seasonal and interannual fluctuations of Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) in Bangladesh, alongside relevant meteorological and hydrological parameters. Employing Google Earth Engine (GEE), we analyze NDVI, EVI, precipitation (PPT), evapotranspiration (ET), and land surface temperature (LST) data from the period spanning 2001 to 2020. The majority of our dataset relies on MODIS satellite imagery. The findings reveal discernible trends in both NDVI and EVI as observed through the Mann-Kendall trend test, with positive Sen's slopes indicating growth rates of 0.004241525/year and 0.002566744/year for NDVI and EVI, respectively. Additionally, EVI exhibits stronger correlations with other hydroclimatic variables compared to NDVI. Notably, EVI showcases an impressive performance with ET, as indicated by an r 2 value of 0.373 and P-value of 6.8119 × 10 −26 , while NDVI displays an r 2 value of 0.17 and P-value of 2.9695 × 10 −11 . Moreover, evapotranspiration can only explain 17% of the variation in NDVI, while no apparent link is observed between NDVI and precipitation. The findings underscore the significance of the EVI in detecting vegetation changes and highlight its robust association with hydroclimatic factors.