What is the net radiative forcing resulting from the impoundment of a hydroelectric reservoir in the boreal region? A case study of the Romaine Complex.

Globally, hydropower is a leading source of renewable energy, however the hydroclimatic impact of the creation of hydroelectric reservoirs in northern regions is not well understood. The impoundment of hydroelectric reservoirs modifies the surface properties and the energy exchange between the earth’s surface and the atmosphere. In warm regions, due to the low albedo of water, most of the solar radiation is absorbed, and impoundment results in a positive radiative forcing. However, in cold regions, due to the presence of ice cover during several months of the year and the high albedos of snow and thick ice, the net annual radiative forcing may be negative. The magnitude of the negative radiative forcing depends on the pre-impoundment environment, as the vegetation type influences the albedo increase due to snow cover over terrestrial environments. A case study of the Romaine hydroelectric complex in Côte-Nord, Quebec (~51°N, ~63°W) is used to evaluate the net radiative forcing resulting from reservoir impoundment in the boreal region. Four-component radiometers are deployed during the open water periods on the Romaine-2 reservoir (2018-present) and year-round at two sites typical of the pre-impoundment environment, Lac Bernard (2022-present) and a forested site (2018-present). First, the radiative forcing is investigated through comparisons of in situ albedo measurements using the natural lake, Lac Bernard, and the primarily black spruce boreal forest site as proxies for post and pre-impoundment conditions. Preliminary results indicate an annual negative radiative forcing due to increased reflection during the ice cover period, as the seasonal variation of the midday albedo of the lake (~0.02 to ~0.8) is greater than that of the forest (~0.08 to ~0.2). The lake’s increased longwave emissions during the later part of the open water period also contributes to the negative radiative forcing. Second, the Canadian Small Lake Model, a 1D dynamic lake model, will be used to spatialize the analysis to the scale of the Romaine-2 reservoir and simulate the radiative forcing resulting from the impoundment under future climate conditions.