Evapotranspiration rates at the Morgan Monroe State Forest AmeriFlux Site: A comparison of results from eddy covariance turbulent flux measurements and sap flow techniques

Comprehensive land surface schemes have been used in regional and global climate models to improve the simulation of exchange processes between the earth's surface and the atmosphere. Assessing the performance of these improved models with respect to the evaporative fluxes at the surface has, however, been hampered by the lack of adequate observational data sets. In this paper, daily, and annual fluxes of evapotranspiration (ET) and transpiration (T) at an AmeriFlux site in the Morgan-Monroe State Forest (MMSF), Indiana, USA, are presented. The site is surrounded by an extensive secondary successional broadleaf forest, in the maple-beech to oak-hickory transition zone. The minimum fetch is 4 km. Average canopy height is 25-27 m. The peak leaf area index (LAI) is 4.7 ± 0.5. The area has a ridge/ravine topography with a relative relief of less than 60 m and an overall drop of 90 m in 4 km. Turbulent flux measurements are obtained by an eddy covariance system at 46 m (1.8 times the canopy height). Sapflow measurements of T, using the Granier technique, are conducted in 9 representative canopy trees in the area around the tower. An intercomparison of ET rates derived from the eddy covariance and T from sapflow are presented for the growing season of 1998.