Evapotranspiration models with canopy resistance for use in climate models, a review

The most advanced climate models are now incorporating effects of vegetation into their surface energy and hydrological balance formulations. These efforts are reviewed here with emphasis on the canopy resistance component through development of a simple generic canopy model that includes the relatively well-established processes common to several canopy submodels. We also review where the land surface treatments diverge, in particular in their consideration of water stress, partial vegetation, within-canopy resistances and computational algorithms for the determination of canopy temperature. The inclusion of canopy submodels in climate models may be of questionable utility without improvements in some aspects of atmospheric simulations, such as the modeled distributions of precipitation and incident surface radiation. Improved treatments of the heterogeneous nature of precipitation and land surface properties are also needed.