| Abstract: | The dependency of the latent heat flux on the over-water fetch on lakes surrounded by tall, dense forest was studied by making use of measurements made on two different-sized lakes. The measurements were made during the NOPEX (Northern Hemisphere Climate-Processes Land Surface Experiment) field campaign. It was found that, in the case of a typical Scandinavian lake with a size of less than 10 km2, the latent heat flux will increase as a function of over-water fetch due to the increase of wind speed and in spite of the increased air humidity. This also has implications on area-averaged fluxes: when two lakes having similar shorelines, lake water temperatures and solar radiation conditions are compared, then the evaporation per unit area is smaller from the smaller lake. When the lakes are large, with fetches of several kilometres, then the significance of sheltering is small. If point measurements 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, otherwise errors of tens of percent may occur. |
