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

Wetland methane (CH 4 ) emission seasonality is a major yet uncertain component of the global CH 4 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 CH 4 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 CH 4 emissions (7 months) in Lake Chad. We demonstrate that the cascading chain of precipitation–wetland inundation–vegetation succession–CH 4 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 CH 4 seasonality and offer critical constraints for improving tropical CH 4 flux estimates.