Temporal and spatial variations in radiation and energy balance across a large freshwater lake in China

- We built an eddy covariance mesonet for Lake Taihu.
- Water heat storage had a similar pattern to net radiation on the diurnal scale.
- Monthly radiation, energy fluxes showed little spatial variations across this lake.
- Annual Bowen ratio was very low.
- 19 Lake evaporation models were evaluated against the eddy covariance data.

The surface radiation and energy exchange processes are important drivers of lake evaporation and the associated hydrological cycle. In this paper, we investigated the temporal and spatial variations in evaporation and the associated radiation and energy fluxes across Lake Taihu, China with an eddy covariance mesonet consisting of three lake sites and one land site. The results indicate that on the diurnal scale, water heat storage showed a similar behavior to net radiation with comparable magnitudes and fueled the substantial nighttime evaporation (48% of annual evaporation). Unlike boreal deep lakes, the monthly mean sensible and latent heat flux was tightly coupled with seasonal variations in net radiation at this large (size 2400 km2), subtropical (30.9-31.6°N) shallow (mean depth 1.9 m) Lake Taihu. On the monthly to annual scales, the radiation and energy fluxes showed little spatial variations across the lake, indicating a lack of sensitivity to wind speed, water depth, water quality and the presence of submerged macrophytes. The annual mean Bowen ratio (0.12-0.13) of the lake was lower than those found in the literature for subtropical and northern lakes and also much lower than that observed at the adjacent land site (0.58). The experimental data were used to evaluate the performance of 19 lake evaporation models of varying complexities.