Integrating Satellite Observations and Hydrological Models to Unravel Large TROPOMI Methane Emissions in South Sudan Wetlands

This study presents a comprehensive investigation of Methane (CH₄) emissions in the wetlands of South Sudan, employing an integrated approach that combines TROPOMI satellite data, river altimetry, and hydrological model outputs. TROPOMI data show a strong increase in CH₄ concentrations over the Sudd wetlands from 2018 to 2022. We quantify CH₄ emissions using these data. We find a twofold emission increase from 2018 to 2019 (9.2 ± 2.4 Tg yr⁻¹) to 2020 to 2022 (16.3 ± 3.3 Tg yr⁻¹). River altimetry data analysis elucidates the interconnected dynamics of river systems and CH₄ emissions. We identify correlations and temporal alignments across South Sudan wetlands catchments. Our findings indicate a clear signature of ENSO driving the wetland dynamics and CH₄ emissions in the Sudd by altering precipitation patterns, hydrology, and temperature, leading to variations in anaerobic conditions conducive to CH₄ production. Significant correlations are found between CH₄ emissions and PCR-GLOBWB-simulated soil moisture dynamics, groundwater recharge, and surface water parameters within specific catchments, underscoring the importance of these parameters on the catchment scale. Lagged correlations were found between hydrological parameters and CH₄ emissions, particularly with PCR-GLOBWB-simulated capillary rise. These correlations shed light on the temporal dynamics of this poorly studied and quantified source of CH₄. Our findings contribute to the current knowledge of wetland CH₄ emissions and highlight the urgency of addressing the complex interplay between hydrology and carbon dynamics in these ecosystems that play a critical role in the global CH₄ budget.