Exchanges between structured canopies and their physical environment: a simple analytical solution for a generic configuration

An analytical solution for the exchange of physical or chemical quantities—other than visible and near infrared radiation—such as water, energy, carbon dioxide, etc. between a canopy and the atmosphere above it can be derived making a limited number of simplifying assumptions. The methodology was developed for the purpose of studying climate/vegetation/ biogeochemistry interactions. Examples of applications demonstrating the generality and flexibility of ESCAPES are provided after presenting the derivation of the solution. The examples include the well-known Penman–Monteith evaporation equation, the isothermal version of the Penman–Monteith evaporation equation, the surface temperature of a wet organism as derived by Paw U, and the temperature and water vapor mixing ratio within the canopy of the BATS soil–vegetation–atmospher–transfer (SVAT) scheme. Taking a slightly more complex angle, an implementation of ESCAPES as a two layer empirical Lagrangian model of evaporation follows. Comparisons with published results obtained with another such model confirm the robustness of the ESCAPES methodology and provide insights into how the estimation of the slope of the vapor pressure curve affects evaporation estimates. The last worked-out example pertains to the use of ESCAPES to integrate the estimation of sensible and latent heat fluxes and canopy photosynthesis. The paper closes with a discussion of the strengths and limitations of the ESCAPES methodology.