Microclimate


A microclimate is a local set of atmospheric conditions that differ from those in the surrounding areas, often with a slight difference but sometimes with a substantial one. The term may refer to areas as small as a few square meters or square feet or as large as many square kilometers or square miles. Because climate is statistical, which implies spatial and temporal variation of the mean values of the describing parameters, within a region there can occur and persist over time sets of statistically distinct conditions, that is, microclimates. Microclimates can be found in most places.
Microclimates exist, for example, near bodies of water which may cool the local atmosphere, or in heavy urban areas where brick, concrete, and asphalt absorb the sun's energy, heat up, and re-radiate that heat to the ambient air: the resulting urban heat island is a kind of microclimate.
Another contributing factor of microclimate is the slope or aspect of an area. South-facing slopes in the Northern Hemisphere and north-facing slopes in the Southern Hemisphere are exposed to more direct sunlight than opposite slopes and are therefore warmer for longer periods of time, giving the slope a warmer microclimate than the areas around the slope. The lowest area of a glen may sometimes frost sooner or harder than a nearby spot uphill, because cold air sinks, a drying breeze may not reach the lowest bottom, and humidity lingers and precipitates, then freezes.

Background

The terminology "micro-climate" first appeared in the 1950s in publications such as Climates in Miniature: A Study of Micro-Climate Environment.
The area in a developed industrial park may vary greatly from a wooded park nearby, as natural flora in parks absorb light and heat in leaves that a building roof or parking lot just radiates back into the air. Advocates of solar energy argue that widespread use of solar collection can mitigate overheating of urban environments by absorbing sunlight and putting it to work instead of heating the foreign surface objects.
A microclimate can offer an opportunity as a small growing region for crops that cannot thrive in the broader area; this concept is often used in permaculture practiced in northern temperate climates. Microclimates can be used to the advantage of gardeners who carefully choose and position their plants. Cities often raise the average temperature by zoning, and a sheltered position can reduce the severity of winter. Roof gardening, however, exposes plants to more extreme temperatures in both summer and winter.
In an urban area, tall buildings create their own microclimate, both by overshadowing large areas and by channeling strong winds to ground level. Wind effects around tall buildings are assessed as part of a microclimate study.
Microclimates can also refer to purpose-made environments, such as those in a room or other enclosure. Microclimates are commonly created and carefully maintained in museum display and storage environments. This can be done using passive methods, such as silica gel, or with active microclimate control devices.
Usually, if the inland areas have a humid continental climate, the coastal areas stay much milder during winter months, in contrast to the hotter summers. This is the case further north on the American west coast, such as in British Columbia, Canada, where Vancouver has an oceanic wet winter with rare frosts, but inland areas that average several degrees warmer in summer have cold and snowy winters.

Soil types

The type of soil found in an area can also affect microclimates. For example, soils heavy in clay can act like pavement, moderating the near ground temperature. On the other hand, if soil has many air pockets, then the heat could be trapped underneath the topsoil, resulting in the increased possibility of frost at ground level.

Cold air pool

The well known examples of cold air pool effect are
Gstettneralm Sinkhole in Austria and Peter Sinks in the US.
The main criterion on the wind speed in order to create a warm air flow penetration into a CAP is the following:
where is the Froude number, — the Brunt–Väisälä frequency, — depth of the valley, and — Froude number at the threshold wind speed.

Craters

The presence of permafrost close to the surface in a crater creates a unique microclimate environment.

Caves and lava tubes

As similar as lava tubes can be to caves which are not formed due to volcanic activity the microclimate within the former is different due to dominant presence of basalt.
Lava tubes and basaltic caves are important astrobiological targets on Earth and Mars.

Plant microclimate

As pointed out by Rudolf Geiger in his book not only climate influences the living plant but the opposite effect of the interaction of plants on their environment can also take place, and is known as plant climate. This effect has important consequences for forests in the midst of a continent; indeed, if forests were not creating their own clouds and water cycle with their efficient evapo-transpiration activity, there would be no forest far away from coasts, as statistically, without any other influence, rainfall occurrence would decrease from the coast towards innland. Planting trees to fight drought has also been proposed in the context of afforestation.

Dams

Artificial reservoirs as well as natural ones create microclimates and often influence the macroscopic climate as well.

Cities and regions known for microclimates

Americas