Microclimates
A microclimate is the distinctive climate of a small-scale area, such as a garden, park, valley or part of a city.
There are 4 ways in which the landscape can alter the microclimate. These are:
- upland areas
- coastal regions
- forests
- urban regions
Aspect is an important concept in microclimates. It is a distinct feature or element in a problem and the visual percept of a region. East or west aspect may affect rainfall or snow cover. This in turn may affect vegetation, humidity, evaporation rates.
URBAN MICROCLIMATE
The table below summarises some of the differences in various weather elements in urban areas compared with rural locations.
The formation of a heat island is the result of the interaction of the following factors:
- the release (and reflection) of heat from industrial and domestic buildings;
- the absorption by concrete, brick and tarmac of heat during the day, and its release into the lower atmosphere at night;
- the reflection of solar radiation by glass buildings and windows. The central business districts of some urban areas can therefore have quite high albedo rates (proportion of light reflected);
- the emission of hygroscopic pollutants from cars and heavy industry act as condensation nuclei, leading to the formation of cloud and smog, which can trap radiation. In some cases, a pollution dome can also build up;
- recent research on London's heat island has shown that the pollution domes can also filter incoming solar radiation, thereby reducing the build up of heat during the day. At night, the dome may trap some of the heat from the day, so these domes might be reducing the sharp differences between urban and rural areas;
- the relative absence of water in urban areas means that less energy is used for evapotranspiration and more is available to heat the lower atmosphere;
- the absence of strong winds to both disperse the heat and bring in cooler air from rural and suburban areas. Indeed, urban heat islands are often most clearly defined on calm summer evenings, often under blocking anticyclones.
