A comparison between reference transpiration and measurements of evaporation for a riparian grassland site

This paper compares direct measurements of evaporation with the values pred icted for reference transpiration. The measurements of actual evaporation w ere made using an eddy correlation device on a grass field adjacent to the river Thames. Measurements of soil moisture and the driving meteorological variables a ere also made. The results showed. that, during a period with m inimal rainfall but no water stress, the cumulative values of reference tra nspiration compared very; well with the cumulative measured evaporation and changes in soil moisture content. However, the values on specific days did not compare well. Following significant rainfall, the measured evaporation increased for a few days, probably due to evaporation of free water from t he canopy or soil. Reference transpiration fell consistently below the meas ured evaporation once the soil moisture deficits exceeded 140 to 150 mm.