Figure 14: Cumulative annual evaporation from 1 March to 28/29 February of the following year, for 2019−20, 2020−21 and 2021−22. Pale green, red, blue and grey bars represent the duration of the respective ice cover periods. Horizontal bars at the end of the energy period represent corrected annual evaporation, compensating for the lack of closure of the energy balance based on the annual EBR (see Table 1).
Few studies have focused on annual scales of lake or reservoir evaporation in the boreal biome. In Canada, Strachan et al. (2016) reported that the evaporation rate at the Eastmain-1 reservoir was 595 mm yr–1, reaching 100 mm month–1in summer and 3.1 mm d–1 from August to October. Rouse et al. (2003) found the annual evaporation at Great Slave Lake to be between 384 mm and 506 mm yr−1 and daily evaporation ranged from 2 mm d–1 in summer to 5 mm d–1 in December. For Lake Tämnaren in Sweden, Heikinheimo et al. (1999) reported 281 mm of evaporation from May to October. Finally, Blanken et al. (2011) found the annual evaporation at Lake Superior to be up to 645 mm. However, it is important to note that these studies were all based on eddy-covariance measurements and did not take into consideration the non-closure of the energy balance, meaning that they did not correct for cumulative evaporation values. This appears to be one major shortcoming in the annual estimation of turbulent heat fluxes.
Table 1 presents important meteorological characteristics for each year of the study period. Note that 2020 experienced the lowest turbine volume in the study, probably due to the upstream flooding of the Romaine-4 reservoir, which might explain the slightly higher evaporation. The highest temperature anomaly by a fair margin occurred in 2021, while wind speed anomalies remained low and constant throughout the study period.
Table 1: Annual characteristics from 2018 to 2021. Non-corrected and corrected total of evaporation, ice cover period, turbine outflow volume, temperature and wind speed anomalies compared to 1991−2020 (ERA5 values) and total net radiation.