Underestimated Dry Season Methane Emissions from Wetlands in the Pantanal

Tropical wetlands contribute ∼30% of the global methane (CH₄) budget. Limited observational constraints on tropical wetland CH₄ emissions lead to large uncertainties and disparities in representing emissions. In this work, we combine remote sensing observations with atmospheric and wetland models to investigate dry season wetland CH₄ emissions from the Pantanal region of South America. We incorporate inundation maps generated from the Cyclone Global Navigation Satellite System (CYGNSS) satellite constellation together with traditional inundation maps to generate an ensemble of wetland CH₄ emission realizations. We challenge these realizations with daily satellite observations for May-July when wetland CH₄ emission predictions diverge. We find that the CYGNSS inundation products predict larger emissions in May, in better agreement with observations. We use the model ensemble to generate an empirical observational constraint on CH₄ emissions independent of choice of inundation map, finding large dry season wetland CH₄ emissions (31.7 ± 13.6 and 32.0 ± 20.2 mg CH₄/m²/day in May and June/July during 2018/2019, respectively). These May/June/July emissions are 2-3 times higher than current models, suggesting that annual wetland emissions may be higher than traditionally simulated. Observed trends in the early dry season indicate that dynamics during this period are of importance in representing tropical wetland CH₄ behaviors.