Variability in modelled reservoir greenhouse gas emissions: comparison of select US hydropower reservoirs against global estimates


 Greenhouse gas (GHG) emissions from reservoirs have most often been evaluated on a global extent through areal scaling or linear-regression models. These models typically rely on a limited number of characteristics such as age, size, and average temperature to estimate per reservoir or areal flux. Such approaches may not be sufficient for describing conditions at all types of reservoirs, especially hydropower reservoirs in temperate climates. In the United States (US), hydropower reservoirs span a wide range of climate regions and have diverse design and operational characteristics compared to those most heavily represented in model literature (i.e., large, tropical reservoirs). We applied the Greenhouse Gas from Reservoirs (G‐res) emissions model to a diverse set of 28 hydropower reservoirs located in a variety of ecological, hydrological, and climate settings that represent the range of sizes and types of facilities within the US hydropower fleet. Resulting estimates for various GHG emission pathways are contextualized in comparison to estimates from the literature for primarily non-US systems. Among these US reservoirs, the net GHG reservoir footprint was less variable and towards the lower end of the range observed from modeling of global hydropower and non-hydropower reservoirs. However, extreme variation in emissions normalized with respect to area and generation highlights the need to be cautious when using area or generation in predicting or expressing emissions footprints, especially given that many of the hydropower reservoirs in the US serve multiple purposes beyond power generation.