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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 (V^sub dep^) 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 V^sub dep^. 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 V^sub dep^. From this, it was found that trees whose LAD [approximate] 0.1 m^sup 2^ m^sup -3^ are the most efficient structures for cloud water deposition. A simple expression for the slope of V^sub dep^ plotted against LAD obtained from the experiments can be useful for predicting total cloud water deposition to forests on large spatial scales.
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1. Introduction
Cloud water (or fog) deposition has long been recognized to be an important factor in the water balance of mountainous vegetation, especially in arid and semiarid regions. Under temperate climates, water for vegetation is supplied sufficiently by rainfall: more than 800-1000 mm yr^sup -1^ in most locations. In contrast, vegetation surviving in arid and semiarid areas generally has to cope with insufficient precipitation. Fog may be an important water resource in such regions. Fog occurring at the surface boundary layer is transported downward by turbulence generated by the strong wind shears at terrestrial surfaces such as plant canopies and is captured by these canopies. If the cloud water captured on foliar and woody...