Unveiling cascading lag effects of wetland methane emissions: Evidence from Lake Chad in Africa

Wetland methane (CH4) emission seasonality is a major yet uncertain component of the global CH4 seasonal cycle, with its quantification primarily limited by the challenges in accurately characterizing wetland dynamics and emission processes. Here, we proposed a remote sensing–based framework to analyze the seasonality of tropical wetland CH4 emission systems by integrating satellite methane inversions with high-resolution wetland inundation mapping (distinguishing open water and inundated vegetation). Our results reveal a strong seasonal amplitude (4.75 teragrams per year) and pronounced seasonal hysteresis between precipitation and CH4 emissions (7 months) in Lake Chad. We demonstrate that the cascading chain of precipitation–wetland inundation–vegetation succession–CH4 emissions drives emission seasonality, characterized by a 3-month lag from precipitation to wetland inundation and a subsequent 4-month lag from inundation to peak emissions. These findings provide comprehensive and mechanistically generalizable insights into tropical wetland CH4 seasonality and offer critical constraints for improving tropical CH4 flux estimates.