The ENVI-met soil model is a crucial component of the software's architecture, simulating the complex interactions within the ground. It calculates how heat and water move through the soil, which in turn influences the urban microclimate and vegetation health.
The model divides the ground into multiple layers of varying thickness, extending from the surface down to a depth of several meters. This layered approach allows for a realistic simulation of how temperature and moisture profiles change throughout the day and night.
Key Processes Handled by the Soil Model
The soil model uses a finite volume method to solve the coupled equations for heat and water transport. It requires several key inputs from the user, including the soil type (e.g., clay, sand, loam) and its properties. Based on these inputs, the model calculates the dynamic changes in soil temperature and volumetric soil moisture for each layer throughout the simulation.
Surface and soil temperature The surface temperature and the distribution of soil temperature is calculated for natural soils and for artificial seal materials down to a depth of -4m. For each vertical grid layer a different soil or sealing material can be chosen in order to simulate different soil structures. The heat conductivity of natural soils is calculated with respect to the actual soil water content.
Soil water content Simulating the water balance of the surface and the soil is a crucial aspect in urban microclimatology. While humid soils can act as cooling devices, dry soils are often hotter than asphalt. In addition, the cooling effect, and -on a longer time perspective- the vitality of vegetation depends on available soil water. ENVI-met dynamically solves the soil hydraulic state of the soil based on Darcy's law taking into account evaporation, water exchange inside the soil and water uptake by plant roots.
Vegetation water supply Plants are living organisms and will only contribute in a positive way to the local microclimate, if enough water is available in the soil within the root zone. Together with the simulation of the soil water content and the 3D root model, the dynamic water supply of the plant and the resulting water extraction from the soil can be calculated.
Water bodies and pounds Water bodies are represented as a special type of soil. The calculated processes inside the water include the transmission and absorption of shortwave radiation inside the water. No second energy balance is used for the ground surface of the water pool, so that heating of shallow systems is lower than under real conditions where the main source of energy is the convection from the water ground surface rather than the absorption of radiation. In addition, no turbulent mixing is included in the model so that the use is restricted to still waters (e.g. lakes).