Methane concentrations over Monsoon Asia as observed by SCIAMACHY: Signals of methane emission from rice cultivation

We have analyzed the column-averaged CH4 concentration (xCH4) using scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) and compared the data with the bottom–up emission inventory data sets and other satellite-derived indices such as the land-surface water coverage (LSWC) and the normalized difference vegetation index (NDVI). The geographical distribution of high CH4 values corresponds to strong emissions from regions where rice is cultivated, as indicated in the inventory maps. The Pearsonʹs correlation coefficients (r) between xCH4 and the rice emission inventory data are observed to be greater than ~ 0.6 over typical rice fields, with outstanding r-values of ~ 0.8 in the Ganges Basin, Myanmar, and Thailand. This suggests that the emission of CH4 from rice cultivation mainly controls the seasonality of the CH4 concentration over such regions. The correlation between xCH4 and LSWC and NDVI is also as large as 0.6. In Southeast Asia, the r-values of xCH4 with bottom–up inventory data that includes all categories are not as high as those with the emission, as estimated from the rice category only. This is indicative of the relative importance of rice emissions among all other emission categories in Southeast Asia.