Thermal Regime and Surface-Atmosphere Energy Exchanges of a Deep Boreal Reservoir
Abstract
Lakes and reservoirs affect the regional climate by acting as heat sink/sources; by evaporating substantial quantities of water nonuniformly throughout the year. Unfortunately, observations of energy exchanges between water bodies and the atmosphere remain rare in northeastern North America, one of the regions with the highest lake density in the world. These water bodies are characterized by two mixing periods and over several months of the year by the presence of an ice cover. This study aims to fill this gap by analyzing observations collected on a northern hydropower reservoir (50.69°N, 63.24°W) characterized by a mean depth of 44 m and a surface area of 85 km2. Two eddy covariance towers were deployed on and around the reservoir for three consecutive years. A pair of optical/microwave scintillometers were also installed on both sides of the reservoirs for a period of a few months to assess regional estimates of latent and sensible heat fluxes (LE and H, respectively). The thermal regime of the reservoir was also monitored using vertical profiles of temperature sensors. Results indicate a mean annual evaporation of 470 ± 20 mm (~50% of the annual precipitation), with 83.5% occurring at a sustained rate from August to freeze-up in late December. Monthly Bowen ratios increase from negative values (due to incoming H) to about 1.5 over the months of June to December. Local (eddy covariance) and regional (scintillometry) fluxes show good correlations (R2=0.85 and 0.64, for H and LE, respectively). However, the evaporation measurements reported by scintillometry are higher than those obtained by the conventional approach (eddy covariance), possibly as a result of spatial heterogeneity in the fluxes. The monthly energy budget closure is excellent between June and October, with a residual of only 10%. The maximum temperature gradient between the epilimnion and hypolimnion layers was 1.4°C/m in mid-September and the maximum thermocline depth was about 30m before full turnover in late October. Ultimately, this study contributes to our understanding of the dynamics of turbulent fluxes and the related thermal regime of a northern hydroelectric reservoir.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.H53D..05P