Wind as a Main Driver of Spatial Variability of Surface Energy Balance Over a Shallow 10²-km² Scale Lake: Lake Kasumigaura, Japan

Lakes have often been treated as one-dimensional entities for energy balance (EB) studies mostly based on point measurements. Therefore, our knowledge of the spatial variability of lake EB is quite limited. We created EB maps of Lake Kasumigaura, a 172-km(2) shallow lake in Japan, with a 90-m horizontal resolution at a 3-hr interval over 5 years based on spatially interpolated meteorological variables and water surface temperature, with turbulent fluxes estimated by the bulk equations. The results indicate that turbulent fluxes and total energy flux into water body G were spatially variable while radiative fluxes were more uniform. The spatial variability of turbulent fluxes averaged over a season, a year, and 5 years was mainly caused by wind speed difference; a longer fetch in downwind areas of the lake resulted in strong winds and higher turbulent fluxes. The spatial difference of turbulent fluxes and quasi-uniform net radiation caused a total energy flux out of the water in the downwind area and a total energy flux into the lake in an upwind area. This spatial difference of G appeared to be compensated by heat transport from the upwind to downwind area through advection due to lake current.