Hydroclimatic Drivers of Modeled Methane Emissions over Volta Lake

Methane (CH₄) emissions from tropical reservoirs are sensitive to hydroclimatic and biogeochemical pressures, yet the dominant controls remain poorly quantified. Here, we combine satellite-derived chlorophyll-a (Chl-a) with a Bayesian upscaling model trained on a global CH₄–Chl-a dataset to estimate long-term (2012–2024) diffusive and ebullitive CH₄ emissions from Volta Lake in Ghana, the world’s largest artificial reservoir by surface area. Modeled emissions show substantial interannual variability and a pronounced post-2016 decline. Annual diffusive emissions ranged from 30.2 - 72.8 Gg CH₄-C yr⁻¹, ebullitive emissions from 109.1 - 211.9 Gg CH₄-C yr⁻¹, yielding combined emissions of 139.2 - 284.7 Gg CH₄-C yr⁻¹. Interannual CH₄ variability closely followed changes in lake-mean Chl-a, consistent with productivity-linked organic matter supply as a key constraint on methanogenesis. In contrast, annual associations between Chl-a (and modeled CH₄) and rainfall, evapotranspiration, or radiation were weak and not statistically significant, suggesting that hydroclimatic influence may operate primarily through seasonal watershed–lake biogeochemical coupling rather than year-to-year mean climate anomalies. These results highlight the sensitivity of Volta Lake methane emissions to long-term shifts in productivity, with implications for reservoir greenhouse gas budgets under changing hydroclimate.