Heat budget estimates for Lake Ikeda, Japan

Heat budget studies of lakes are essential components of efficient lake water management as they give direct information on evaporation and thus the lake water budget. A one-dimensional heat transfer model which includes vertical turbulent mixing in lake water and heat exchange between the lake and the atmosphere was developed and applied to estimate heat budget of Lake Ikeda from 1981 to 2005. The lake is in southern Japan, has a mean water depth of 125 m, and is an important water resource for agriculture, municipal water supply, and fisheries. The computed lake water temperatures were in good agreement with observed temperatures. The model reproduced both the thermal stratification characteristics and the uniform vertical 10 °C temperature profile that occurs in Lake Ikeda every February. When the storage heat was suitably quantified, the latent heat computed on a monthly basis by the model also agreed well with those calculated by both the Bowen ratio and Priestley–Taylor methods. Analysis of the heat budget for a 25-year period from 1981 to 2005 showed that the lake accumulates heat from March to August and releases it through latent and sensible heat under a small net radiation condition from September to February. Maximum latent heat occurs in October and minimum latent heat in April. The annual average evaporation is 938 mm and the autumn evaporation from September to November accounts for about 40% of the total annual evaporation.