Footprint climatologies for evapotranspiration in a boreal catchment

A footprint model was applied to the micrometeorological monitoring of evapotranspiration (ET) in a boreal forest catchment. The footprints were weighted by the measured value of ET to give the footprint that determines the ET flux. The resulting footprint climatology was used to investigate the effect of different averaging times, from a single day to a whole season. The climatology defined the area where 90% of ET originates as a reasonable indicator of the most important part of the landscape sampled. The analysis showed that two 12-m high towers would be needed to fully sample the 90% footprint contour of ET in the 0.5 km(2) catchment study area on a seasonal basis. We conclude that it would be difficult to use micrometeorological techniques to monitor ET without doing a quantitative footprint analysis to define the sampled area. (C) 1998 Atomic Energy of Canada Ltd. Published by Elsevier Science B.V.