Atmospheric CH4 Dynamics of South-West Bangladesh: A Google Earth Engine-Based Remote Sensing Approach

Abstract

A severe contributor to global warming, Methane (CH4) is a significant element of Green House Gases (GHGs). Both anthropogenic and natural sources are responsible for its emission. The development of satellites for remote sensing has made it convenient to study the spatiotemporal distribution of any gaseous component. Tropospheric Monitoring Instrument (TROPOMI) integrated with Sentinel-5 Precursor (Sentinel-5P) satellite is proven efficient in studying CH4. Sentinel-5P TROPOMI CH4 data from February 2019 to September 2022 has been used to research southwest districts with the Sundarbans mangrove forest. Besides, satellite data from MODIS (Moderate Resolution Imaging Spectroradiometer), ERA5 and Climate Hazards Group Infrared Precipitation with Station data (CHIRPS) are used to analyse methane changes from 2019 to 2022. All these diverse datasets have been retrieved by using Google Earth Engine (GEE) platform. CH4 emission shows an increasing trend over the study area. The emission rate is higher (more than 1900 to 1950 ppb) in all districts during the dry winter season, especially from January to March. Particularly, cropland and water have regular and higher emissions. On the contrary, bare ground and rangeland have irregular and higher emissions. Built area exerts higher emission trend (more than 1900 ppb) in Satkhira district. All districts, including the Sundarbans, have shown positive relation with Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI), indicating single cropland and shrimp aquaculture as significant emitters. The presence of massive vegetation and waterbodies in the Sundarbans is responsible for low emissions (below 1900 ppb). Sundarbans have been found with an anomalous correlation with meteorological variables. Apart from the anthropogenic perspective, there could also be potential environmental and geological sources of CH4 emissions.