The microclimate is a local atmospheric zone where the climate differs from the surrounding area. The term may refer to areas as small as a few square feet (for example a garden bed) or as large as many square miles. Microclimates exist, for example, near bodies of water which may cool the local atmosphere, or in heavily urban areas where brick, concrete, and asphalt absorb the sun's energy, heat up, and reradiate that heat to the ambient air: the resulting urban heat island is a kind of microclimate. Microclimates can be found in most places.

Another contributing factor to 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.

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.[citation needed]

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.

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.

Soil types[edit]

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 [5]

Cities and regions known for microclimates[edit]

San Francisco is a city with microclimates and submicroclimates. Due to the city's varied

topography and influence from the prevailing summer marine layer, weather conditions can vary by as much as 9°F (5°C) from block to block.[1]

The region as a whole, known as the San Francisco Bay area can have a wide range of extremes in temperature. In the basins and valleys adjoining the coast, climate is subject to wide variations within short distances as a result of the influence of topography on the circulation of marine air. The San Francisco Bay Area offers many varieties of climate within a few miles. In the Bay Area, for example, the average maximum temperature in July is about 64 °F (18 °C) at Half Moon Bay on the coast, 87 °F (31 °C) at Walnut Creek only 25 miles (40 km) inland, and 95 °F (35 °C) at Tracy, just 50 miles (80 km) inland.[2]

The Los Angeles and San Diego areas are also subject to phenomena-typical of a microclimate. As such, the temperatures can vary as much as 18°F (10°C) between inland areas and the coast, with a temperature gradient of over one degree per mile (1.6 km) from the coast inland. Southern California has also a weather phenomenon called "June Gloom or May Grey", which sometimes gives overcast or foggy skies in the morning at the coast, but usually gives sunny skies by noon, during late spring and early summer.

Calgary, Alberta, is also known for its microclimates. Especially notable are the differences between the downtown and river valley/flood plain regions and the areas to the west and north. This is largely due to an elevation difference within the city's boundaries of over 1,000 ft (300 m), but can also be attributed somewhat, to the effects of the seasonal Chinooks.[3]

Halifax, Nova Scotia, also has numerous microclimates. Coastal temperatures and weather conditions can differ considerably from areas located just 5–15 km inland. This is true in all seasons. Varying elevations are common throughout the city, and it is even possible to experience several microclimates while travelling on a single highway due to these changing elevations.

Santiago, Chile, and Villa de Merlo, Argentina, are also subject to microclimates.

Known for its wines, the Ticino region in Switzerland benefits from a microclimate in which palm trees and banana trees grow.

Gran Canaria is called "Miniature Continent" for its rich variety of microclimates.

Biddulph Grange is very rich with microclimates as a result of the large dips and variety of very large trees alongside a large amount of water.

Mascot, located in New South Wales, Australia, is also noted as a microclimate.

Leeds, located in England is known to have a number of microclimates because of the number of valleys surrounding the city centre.

Amman, Jordan has extreme examples of microclimate, and almost every neighbourhood exhibits its own weather.[4] It is known among locals that some boroughs such as the northern and western suburbs are among the coldest in the city, and can be experiencing frost or snow whilst other warmer districts such as the city centre can be at much warmer

temperatures at the same time.

ClimateThe climate of the earth consists of a series of interlinked physical systems powered by the sun.In the built environment we are generally concerned with local climatic systems in particular:·Macro-climate the climate of a larger area such as a region or a country·Micro-climate the variations in localised climate around a buildingThe macro and micro climate has a very important effect on both the energy performance and environmental performance of buildings, both in the heating season and in summer.

The site and design of a building can have a profound effect upon the interaction between a building and its environment.

The building site affects exposure to the prevailing wind, the solar radiation the building receives, pollution levels, temperatures and rain penetration.Site and macro climateThe orientation of the building affects solar gains and exposure to the prevailing wind (ventilation).The location of neighbouring trees and buildings affects the solar gains (shading) and wind patterns.

Neighbouring trees and buildings also protect the building from driving rain.

Macro ClimateThe macro climate around a building cannot be affected by any design changes, however the building design can be developed with a knowledge of the macro climate in which the building is located. General climatic data give an idea of the local climatic severity:·Seasonal accumulated temperature difference (degree day) are a measure of the outside air temperature, though do not acount for available solar·Typical wind speeds and direction·Annual totals of Global Horizontal Solar Radiation·The driving rain index (DRI) relates to the amount of moisture contained in exposed surfaces and will affect thermal conductivity of external surfaces.

This Metereological data gives a general impression of the climate at the site of a building and the building design can be planned accordingly. However the building itself and surrounding geography will affect the local climate.

Micro-ClimateThe site of a building may have a many micro climates caused by the presence of hills valleys, slopes, streams and other buildings.Micro Climate – Effect of Local TerrainSurrounding slopes have important effects on air movement, especially at the bottom of a hollow. In hollows air warmed by the rises upwards due to buoyancy effects (anabatic flow), to be replaced by cooler air drifting down the slope (katabatic flow).

The result is that valey floors are significantly colder than locations part way up the slope. Katabatic flows often result in frosts persisting for longer in low lying locations. The most favourable location in a valley is known as the thermal belt, lying just above the level to which pools of cold air build up, but below the height at which exposure to wind increases.

The crests of hills and ridges have unfavourable wind velocity profiles, the wind flow is compressed (as happens with an aerofoil) leading to high wind velocities.

Micro-Climate – Effects of BuildingsBuildings themselves create further micro-climates by shading the ground,changing wind flow patterns.One example of how buildings affect the local climate is the heat island effect inlarge cities where the average temperature is higher than the surrounding area:Solar energy absorbed and re-emitted from building surfaces, pavements roadsetc. creates a warming effect on the surrounding air. Also the large quantities ofbuildings break up the wind flow, reducing wind speeds and causing the warmair to remain stagnant in the city. This also causes increased pollution as wellas temperatures

The presence of local high rise buildings can degrade the local climate as wind speed at ground level can be significantly increased, while extensive shadows block access to sunlight for long periods, increasing space heating costs in surrounding buildings.Improving Micro Climate through DesignThe aims of enhancing Micro-Climate around Buildings:·Reduce costs of winter heating·Reduce summer overheating and the need for cooling·Maximise outdoor comfort in summer and winterAlso:·Improve durability of building material (reduced rain penetration)·Provide a better visual environment in spaces around buildings·Encourage growth of plants·Discourage growth of mosses and algae·Facilitate open air drying of clothesMeans of enhancing the micro climate around a building include:Solar Access:Allow maximum daylight into space and buildingsAllow maximum solar radiation into space and buildingsShade space and windows from prolonged exposure to summer sunProtect space and windows from glareWind ProtectionProtect space and buildings from prevailing winds and cold (e.g. North/East) winds.Prevent buildings and terrain features from generating turbulenceProtect spaces and buildings from driving rain and snowProtect space and buildings from katabatic flows, while retaining enough air movement to disperse pollutants.

Features

Provide thermal mass to moderate extreme temperaturesUse vegetation for sun shading and wind protection (transpiration helps moderate high temperatures).Provide surfaces that drain readily.Provide water for cooling be evaporation (pools and fountains)Factors Affecting Micro ClimateOutside Designers Control

Area and local climate

Site surroundings

Site shape

Topographic features

Surrounding Buildings

Two main possibilities for influencing Micro Climate are Solar Access and WindControlSolar AccessSolar access to a site is often a case of minimising solar overheating in summer while maximising solar access during the winter.Buildings with a heating requirement should be orientated north south with maximum glazing on the south face.Deciduous trees offer an excellent means of site shading, with shading being reduced in winter when the trees lose their leaves.The colour of surrounding surfaces will

have a pronounced effect on the solarradiation available to the building. Light coloured paving will increase the radiation reflected from the ground into the building. Paving stones will also provide external thermal mass, moderating temperature swings immediately adjacent to the building.Grass planted outside a building will reduce the ground reflected solar.Use of courtyards and water can also moderate the effects of high temperatures on summer.

Wind ControlThe form of the building can have a great effect on the impact of the wind:·Avoidance of the building flank facing the wind·Avoidance of funnel-like gaps between buildings·Avoidance of flat roofed buildings and cubical forms·Avoid piercing buildings at ground level·Avoid abrupt changes in building

heights·Orientate long axis of the building parallel to the direction of the wind·Use podium to limit down draught at ground level·Use pitched rather than flat roofs and stepped forms for higher buildings·Groups of buildings can be arranged inirregular patterns to avoid wind tunneling.Coniferous trees and fencing and other landscape features such as mounds of earth and hedges can also reduce the impact of wind and driving rain on the buildingstructure.Enhanced Micro Climate and Energy SavingIncreased external air temperature leading to reduced space heating reduction:increase solar access to site, wind protection, external thermal mass, quick drying surfaces.Reduced Air Change Rate, internal air movement and decreased external surface connective heat transfer: reduced pressure driven ventilation by wind protection.Reduced moisture effects on fabric: less wetting of fabric and energy loss due to evaporation from wet surfaces by protecting from driving rain and providing adequate surface drainage.