LATENT-HEAT FLUX FROM SMALL SHELTERED LAKES

The dependency of the latent heat flux on the over-water fetch on lake s surrounded by tall, dense forest was studied by making use of measur ements made on two different-sized lakes. The measurements were made d uring the NOPEX (Northern Hemisphere Climate-Processes Land Surface Ex periment) field campaign. It was found that, in the case of a typical Scandinavian lake with a size of less than 10 km(2), the latent heat f lux will increase as a function of over-water fetch due to the increas e of wind speed and in spite of the increased air humidity. This also has implications on area-averaged fluxes: when two lakes having simila r shorelines, lake water temperatures and solar radiation conditions a re compared, then the evaporation per unit area is smaller from the sm aller lake. When the lakes are large, with fetches of several kilometr es, then the significance of sheltering is small. If point measurement s are used for the estimation of area-averaged latent heat fluxes from lakes with short fetches and forested shorelines then the distance of the measuring site from the shoreline should be taken into account, o therwise errors of tens of percent may occur.