Wind flow

Cities worldwide prepare themselves with different devices to adapt to the negative consequences of climate risks like heat waves, heavy rain and stormy winds. The wind situation differs considerably between urban areas and more open spaces.

Through the three-dimensional structure and disposition of building volumes within cities it is possible to experience areas of high wind speeds and turbulent wind gusts. The opposite situation can be found in the immediate vicinity of those areas. Zones with very low wind speed and stagnating air masses can increase the effect of heat stress, the accumulation of pollutants and promote the development of varmints in vegetation.

Through in-situ measurements it is possible to collect local?information on wind speed and direction, but in order to obtain spatially inclusive and comprehensive data, especially when considering future planning scenarios, wind tunnel experiments or computational fluid analysis (CFD) are absolutely essential. Since wind tunnel studies are not only very complex, but can also represent only a few partial aspects of the possible microclimatological conditions, numerical studies have established themselves as standard in research and practice with the aid of simulation programs.

The ENVI_MET software is the world‘s only numerical climate model to analyse the interactions between urban development, architecture and landscape architecture as well as the microclimate and air quality down to a scale of one metre. It is thus possible to investigate the interactions between climatological conditions and local environmental design.

Solar radiation

As urbanization is predicted to increase dramatically within the next 30 years, the urban heat island effect, in which an urban area is remarkably warmer than surrounding non-urbanized areas, will most likely increase in coming decades. However, this urbanization trend is still not been included in many climate model projections and hardly addressed as a design criteria in planning and design processes.

In most countries, the summer climate is affected by urban heat, humidity and high solar radiation. The sunlight that hits the builtup areas is often absorbed by dark, non-reflective surfaces that then release the heat into the local environment. In addition, low wind speeds in summertime contribute significantly to an increased intensity of urban heat.

From all microclimate elements, solar radiation is the component with the highest spatial and temporal variation within urban areas. Shading from buildings and other elements on the one hand – and the reflection of radiation on bright or glassy facades on the other – can create complex patterns of radiation fluxes. So, understanding and analysing local exposure to solar radiation and daylight over the year is essential for all urban and architectural planning processes. Both too much and too little access to sunlight can lead to uncomfortable living conditions for both humans and plants in indoor and outdoor spaces.

ENVI_MET provides sophisticated three-dimensional analysis tools to calculate and trace the distribution of short-wave direct, diffuse and reflected solar radiation within the outdoor environment. In contrast to other software programs that allow the simulation of radiation fluxes, ENVI_MET can also simulate airflow, heat and vapour exchange in urban areas, with a high temporal and spatial resolution using the same input data as for the solar analysis.