The ENVI-met vegetation model is a core component of the software, designed to simulate the physical and biological processes of plants and their influence on the urban microclimate. This model represents vegetation in three dimensions, allowing for a detailed and realistic simulation of plant geometry and structure, from simple grass cover to a full grown complex tree.
The vegetation model is fully integrated with the other components of ENVI-met. It receives inputs on soil moisture from the soil model and on radiation and wind conditions from the atmospheric model. In return, the vegetation model provides the atmospheric model with updated values for latent and sensible heat fluxes, directly influencing the simulation of air temperature, humidity, and airflow patterns.
Key Functions of the Vegetation Model
The model's primary function is to quantify the dynamic exchange of energy, water, and momentum between plants and their surrounding atmosphere.
Evapotranspiration: This process is a significant mechanism for microclimatic cooling. The model calculates the latent heat flux from plants through transpiration, which is a function of solar radiation, air temperature, and available soil water.
Radiation Interception and Shading: Based on a plant's physical structure and its Leaf Area Density (LAD), the model calculates the interception of shortwave (solar) radiation. This process creates shaded areas on the ground and building surfaces, which reduces surface temperatures and subsequent heat transfer to the air.
Aerodynamic and Thermal Effects: Vegetation modifies local airflow. The model accounts for the aerodynamic roughness created by plants, which can reduce wind speeds. It also calculates the transfer of heat from foliage to the surrounding air, contributing to the overall energy balance.
Pollutant Deposition: The model simulates the physical deposition of particulate matter and other pollutants onto plant surfaces, providing a method to assess the air quality benefits of urban vegetation.
Foliage temperature The temperature of the leafs is calculated by solving the energy balance of the leaf surface with respect to the actual meteorological and plant physiological conditions for each grid box of the plant canopy. The health status of the plant and the water supply by the soil regulate, beside other factors, the plants transpiration rate and thereby the leaf temperature. ENVI-met uses a sophisticated model to simulate the stomata behaviour of the vegetation in response to microclimate, CO2 availability and water stress level.