Author(s): Manu Seth; Finan Weldemikael; Melissa Sondermann; Maria Ubierna; David Finger; Cristina Diez

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Abstract: Hydropower reservoirs are increasingly recognised as dynamic sources of methane (CH₄) and carbon dioxide (CO₂), with emissions driven by biological productivity, thermal stratification, hydrological variability, and operational cycles that put at risk hydropower’s clean credentials. Spatial heterogeneity, strong seasonality, and short-lived emission spikes, such as turnover events, rapid inflows, or drawdowns, make accurate quantification challenging. Traditional field-based methods provide high-precision data but are logistically demanding, limited in spatial coverage, and challenging to harmonise across regions, including remote and cold-climate systems. As demand for clean energy and transparent, scalable climate reporting grows, there is an urgent need for observation-driven approaches that enable consistent monitoring of hydropower reservoirs at fine temporal and spatial resolutions. Satellite Earth Observation (EO) has emerged as a transformative tool for characterising the environmental conditions that underpin GHG production and release. Rather than attempting to measure methane directly, EO enables the retrieval of biophysical and thermal proxies that describe trophic status, carbon inputs, thermal structure, sediment-water interactions, and hydrological behaviour. These proxies provide the environmental context required to model CH₄ and CO₂ dynamics with greater robustness and scalability. We propose a structured framework for organising EO-derived indicators relevant to reservoir GHG processes, grouped into two complementary categories:

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Year: 2026