Development of a Land Surface Model Including Cloud Water Deposition on Vegetation

Abstract

A land surface model including cloud (fog) water deposition on vegetation was developed to better predict the heat and water exchanges between the biosphere and atmosphere. A new scheme to calculate cloud water deposition on vegetation was implemented in this model. High performance of the model was confirmed by comparison of calculated heat and cloud water flux over a forest with measurements. The new model provided a better prediction of measured turbulent and gravitational fluxes of cloud water over the canopy than the commonly used cloud water deposition model. In addition, simple linear relationships between wind speed over the canopy (|U|) and deposition velocity of cloud water (Vdep) were found both in measurements and in the calculations. Numerical experiments using the model were performed to study the influences of two types of leaves (needle and broad leaves) and canopy structure parameters (total leaf area index and canopy height) on Vdep. When the size of broad leaves is small, they can capture larger amounts of cloud water than needle leaves with the same canopy structure. The relationship between aerodynamic and canopy conductances for cloud water at a given total leaf area density (LAD) strongly influenced Vdep. From this, it was found that trees whose LAD ≈ 0.1 m2 m?3 are the most efficient structures for cloud water deposition. A simple expression for the slope of Vdep plotted against LAD obtained from the experiments can be useful for predicting total cloud water deposition to forests on large spatial scales.