Spatiotemporal investigation of near-surface CH and factors influencing CH over South, East, and Southeast Asia.

Methane (CH) is the second most abundant greenhouse gas after CO, which plays the most important role in global and regional climate change. To explore the long-term spatiotemporal variations of near-surface CH, datasets were extracted from Greenhouse gases Observing SATellite (GOSAT), and the Copernicus Atmospheric Monitoring Service (CAMS) reanalyzed datasets from June 2009 to September 2020 over South, East, and Southeast Asia. The accuracy of near-surface CH from GOSAT and CAMS was verified against surface observatory stations available in the study region to confirm both dataset applicability and results showed significant correlations. Temporal plots revealed continuous inflation in the near-surface CH with a significant seasonal and monthly variation in the study region. To explore the factors affecting near-surface CH distribution, near-surface CH relationship with anthropogenic emission, NDVI data, wind speed, temperature, precipitation, soil moisture, and relative humidity were investigated. The results showed a significant contribution of anthropogenic emissions with near-surface CH. Regression and correlation analysis showed a significant positive correlation between NDVI data and near-surface CH from GOSAT and CAMS, while a significant negative correlation was found between wind and near-surface CH. In the case of temperature, soil moisture, and near-surface CH from GOSAT and CAMS over high CH regions of the study area showed a significant positive correlation. However significant negative correlations were found between precipitation and relative humidity with GOSAT and CAMS datasets over high CH regions in South, East, and Southeast Asia. Moreover, these climatic factors showed no significant correlation within the low near-surface CH areas in our study region. Our study results showed that anthropogenic emissions, NDVI data, wind speed, temperature, precipitation, soil moisture, and humidity could significantly affect the near-surface CH over South, East, and Southeast Asia.