Microclimate

A small scale terrain depression which creates a frost hollow, due to localized atmospheric conditions.

A microclimate (or micro-climate) refers to localized atmospheric conditions in the near-surface layer, which includes the air immediately above a surface as well as the shallow soil and water environments below it. A microclimate can range in size from a few meters to at most a few kilometers across. It is characterized by a set of persistent, measurable differences in the climate conditions from those in the adjacent surrounding areas. These differences may be subtle or pronounced when evaluated over a diurnal (day-night) or seasonal cycle.

Surfaces associated with microclimates include both natural and human made materials, on land and water.

Microclimates are directly caused by weather and climate processes. These processes can be shaped or influenced by contributing factors, such as topography, soil composition, vegetation structure and plant diversity as well as the mass of nearby objects, natural or human made.

Because microclimates are hyperlocal systems, scientific instruments and best practices accounting for the physics of heat transfer and the measurement of microclimate air temperatures are needed to produce accurate results.

Important applications of microclimate knowledge include, agriculture and microclimate engineering, climate change impact, reforestation planning, and energy management.

Scales of climate

Climate is commonly described as a hierarchy of spatial scales which are nested and interrelated. Understanding the scale at which climate is measured and the relationships between the classifications, provides important context.

A Macroclimate is the climate of a large region, typically covering an area defined as hundred to thousands of kilometers. It is shaped by broad atmospheric patterns. Mesoclimates are nested within the macroclimate and are defined by the topography and features of an area. Mesoclimates range in size between tens to hundreds of kilometers. Microclimates are present at much smaller scales, mostly controlled by the properties of the area and energy exchanges.

As spatial scale decreases from macro to micro, the influence of local surfaces, shade, wind obstruction and moisture present become dominant and have significant influence on the related properties of weather.

Microclimates occur within the Planetary boundary layer, which is the lowest level of atmosphere directly influenced by dynamics on the Earth's surface.

Tree ferns thrive in a protected dell area in the Lost Gardens of Heligan, in Cornwall, England, latitude 50° 15'N.

Causes of microclimates

Microclimates develop when temperature and humidity are altered by exchanges of heat, moisture and air between the Earth's surface and the atmosphere.

These localized atmospheric conditions arise from differences in sunlight, heat, wind, and moisture near the surface. Terrain, vegetation, soil, water, and human-made features help shape and modify these conditions.

Direct physical processes

Fundamental physical processes which directly create microclimate variation are:

Contributing environmental factors that shape microclimates

This conceptual diagram illustrates how terrain elevation, vegetation, and building mass structures can create sheltered conditions that influence localized atmospheric properties such as temperature, wind and humidity.

In addition to the direct physical processes, there are characteristics in the environment which can influence the development and persistence of microclimates.

How to measure microclimates

The measurement of microclimates presents challenges not encountered with observing broader regional atmospheric conditions. Environmental conditions often vary considerably over short distances due to differences in shading, terrain, vegetation and surface materials. Measurements are also highly sensitive to placement, exposure and the design of the sensor itself. Temperature sensors record their own physical temperature which can be influenced by their materials, heat exchange, and solar radiation exposure. Instruments placed above the near surface layer may be subject to conditions which are different from the microclimate being observed. Due to these challenges, the accurate measurement of microclimates requires careful sensor placement, radiation shielding, and thoughtful analysis of observation data.

Microscale meteorology is the scientific field which studies atmospheric processes responsible for the creation of microclimates. It focused on processes which occur in distances as small centimeters to a few kilometers, which are the same scales at which microclimates exist. This field supplies the methods and techniques by which accurate microclimate measurement can occur.

Spatial resolution is a key concept related to understanding the measurement of microclimates. Because environmental conditions can vary dramatically over very small distances, microclimate observation often uses a network of sensors placed more densely than those in conventional weather station deployments. These networks allow localized atmospheric variability to be observed more accurately. Examples of these meteorological networks are mesonets and micronets, which consist of automated weather stations measuring air temperature, humidity, wind, and solar radiation. Observations are typically reported in frequent intervals, often every few minutes. The closely spaced sensors and frequent sampling provide the fine-scale, high-resolution data needed to characterize microclimate patterns.

Environmental monitoring is the systematic collection of data over time to understand conditions and detect changes. By continuously monitoring the microclimate over time it allows researchers to observe daily and seasonal fluctuations. This reveals how microclimates respond to changes in environmental conditions.

Importance of microclimates

The study of microclimates provides important insights across multiple scientific and applied science fields by helping researchers understand how localized environmental conditions influence both natural and human-made systems.

Examples of microclimates

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 radiates back into the air.

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 in places such as British Columbia, 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.

Craters

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

Caves

Caves are important geologic formations that can house unique and delicate geologic/biological environments. The vast majority of caves found are made of calcium carbonates such as limestone. In these dissolution environments, many species of flora and fauna find home. The mixture of water content within the cave atmosphere, air pressure, geochemistry of the cave rock as well as the waste product from these species can combine to make unique microclimates within cave systems.

The speleogenetic effect is an observed and studied process of air circulation within cave environments brought on by convection. In phreatic conditions the cave surfaces are exposed to the enclosed air (as opposed to submerged and interacting with water from the water table in vadose conditions). This air circulates water particles that condense on cave walls and formations such as speleothems. This condensing water has been found to contribute to cave wall erosion and the formation of morphological features. Some examples of this can be found in the limestone walls of Grotta Giusti; a thermal cave near Monsummano, Lucca, Italy. Any process that leads to an increase or decrease in chemical/physical processes will subsequently impact the environment within that system. Air density within caves, which directly relates to the convection processes, is determined by the air temperature, humidity, and pressure. In enclosed cave environments, the introduction of bacteria, algae, plants, animals, or human interference can change any one of these factors therefore altering the microenvironment within the cave. There are over 750 caves worldwide that are available for people to visit. The constant human traffic through these cave environments can have a negative effect on the microclimates as well as on the geological and archeological findings. Factors that play into the deterioration of these environments include nearby deforestation, agriculture operations, water exploitation, mining, and tourist operations.

The speleogenetic effect of normal caves tends to show a slow circulation of air. In unique conditions where acids are present, the effects of erosion and changes to the microenvironment can be drastically enhanced. One example is the effect of the presence of hydrosulfuric acid(H2S). When the oxidized hydrosulfuric acid chemically alters to sulfuric acid(H2SO4), this acid starts to react with the calcium carbonate rock at much higher rates. The water involved in this reaction tends to have a high pH of 3 which renders the water almost unlivable for many bacteria and algae. An example of this can be found in the Grotta Grande del Vento cave in Ancona, Italy.

Dams

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

Sinkholes

Examples of sinkholes and the associated cold air pool (CAP) effect are Gstettneralm Sinkhole in Austria (lowest recorded temperature −53 °C (−63 °F)) and Peter Sinks in the US.

Slopes

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.

Cities and regions known for microclimates

Americas

Europe

Asia and Oceania

Background and other uses

The terminology "micro-climate" first appeared in the 1950s in publications such as Climates in Miniature: A Study of Micro-Climate Environment (Thomas Bedford Franklin, 1955).

The term microclimate is also used in the healthcare industry. It describes the localized environment of the skin, specifically temperature, humidity and air movement and how it impacts wound care.

See also

References

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