Evaporation from Lake Kasumigaura: annual totals and variability in time and space

Abstract

Evaporation E from Lake Kasumigaura, the second larg- est lake in Japan, was estimated continuously at a 3-h inter- val for the period of 2008–2012 by means of a bulk formula- tion applied to 23,468 grids covering the whole lake surface. A functional form of the bulk coefficient was determined from eddy correlation measurements at the central part of the lake. Wind speed (U), temperature, humidity, and infra- red radiation surface temperature, from which the specific humidity qs of the water surface was determined, were also measured. Specific humidity q and U at 10 m above the sur- face of each grid were derived from routine measurements at meteorological stations in and around the lake, by applying the Kriging interpolation scheme. This operation produced not only the totals but also the horizontal variation in E. The mean annual E was estimated as 911 (± 42) mm, which is within the range of previous estimates of 671–1003 mm/yr. Seasonally, E followed the change in net radiation with a short (< 1 month) phase delay caused by stored energy in the water body. Year-to-year variation was small. Horizontally E tended to be larger in the central and southern parts of the lake, reflecting stronger wind regime there