3. Microclimate

A microclimate is the distinctive climate of a small-scale area, such as a garden, park, valley or part of a city. The weather variables in a microclimate, such as temperature, rainfall, wind or humidity, may be subtly different to the conditions prevailing over the area as a whole and from those that might be reasonably expected under certain types of pressure or cloud cover. Indeed, it is the mixture of many, slightly different microclimates that actually makes up the climate for a town, city or wood.

Microclimate can be caused by several factors such as

♤ Near water bodies

♤ Heat retaining capacity of urban areas

♤ Slope of mountains

♤ Absence of vegetation such as in central business districts

♤ Large presence of vegetation such in protected areas

♤ Soil type

There is a distinctive microclimate for every type of environment on the Earth’s surface:

Upland regions

Upland areas have a specific type of climate that is notably different from the surrounding lower levels. Temperature usually falls with height at a rate of between 5 and 10 °C per 1,000 metres, depending on the humidity of the air. This means that even quite modest upland regions can be significantly colder on average.

Occasionally, a temperature inversion5 can make air warmer in upland regions, but such conditions rarely last for long. With higher hills and mountains, the average temperatures can be so much lower that winters are longer and summers much shorter. Higher ground also tends

5 Temperature inversion – It is a deviation from the normal change of an atmospheric temperature with altitude i.e., an increase in temperature with height, or to the layer ("inversion layer") within which such an increase occurs.

to be windier, which makes for harsher winter weather. Katabatic wind6 also creates cold conditions in the valley. The effect of this is that plants and animals are often different from those at low levels.

Coastal regions

The coastal climate is influenced by both the land and sea between which the coast forms a boundary. The thermal properties of water are such that the sea maintains a relatively constant day to day temperature compared with the land. The sea also takes a long time to heat up during the summer months and, conversely, a long time to cool down during the winter. Coastal microclimates display different characteristics depending on where they occur on the earth’s surface. In the tropics, sea temperatures change little and the coastal climate depends on the effects caused by the daytime heating and night-time cooling of the land. In temperate latitudes, the coastal climate owes more to the influence of the sea than of the land and coasts are usually milder than inland during the winter and cooler in the summer. Around the poles, sea temperatures remain low due to the presence of ice, and the position of the coast itself can change as ice thaws and the sea re-freezes.