Microclimates

Analysing Climates

Choropleth maps are colour-coded maps with differences in shading techniques that represent a certain value, such as temperature or precipitation.

Climate graphs are useful graphs that combine a bar graph (indicating precipitation) and a line graph (indicating temperature) to inform us of the average yearly climatic conditions in a region.

Factors Affecting Microclimates

A range of biotic and abiotic factors can affect microclimates. Microclimates can also be affected by geologic or man-made features that can cause precipitation, heat pockets, or additional shading.

Topography

On a large scale, weather systems are predictable due to the Earth's rotation and the interaction between ocean and land. However, these patterns can be disrupted by local topography, such as aspect and relief.

Fig. 1 – Mountain topography is steep and uneven. Source: unsplash.com

Aspect can determine the amount of sunlight an area receives. In turn, this affects temperature and shading. In the Northern Hemisphere, south-facing slopes are exposed to more direct sunlight, casting longer shadows on the opposite side of the slope. This affects the species of plants present. However, it's not just mountains that lead to microclimates. Small dips and depressions in valleys and low-lying areas can form collection points for cold air, leading to frost pockets in winter.

Areas at a higher altitude experience a different microclimate. Temperatures are colder and oxygen availability is lower, limiting the species that can survive in these conditions.

Soil

Soil composition affects an area's microclimate through water retention or evaporation. For example, clay soils retain more water than sandy soils. Soil moisture retention influences the humidity and temperature above it. The degree of soil coverage can also impact temperature – bare soils reflect more light and heat.

Vegetation

Vegetation interacts with soil and water in the microclimate in many ways. It covers the soil, preventing heat loss and radiation, releases water via evapotranspiration, regulates temperature, filters the air, and acts as a windbreak or suntrap.

Artificial Structures

Artificial structures can modify climates – absorbing and releasing heat or providing protection from wind and sunlight.

Even something minor, like a large stone, can shelter invertebrates and amphibians from extremes of temperature and moisture.

Water Bodies

Bodies of water can positively affect the microclimate. Evaporation is enhanced, which is associated with an uptake of latent heat and removal of thermal energy from the body of water. As a result, bodies of water provide a cooling source.

Macroclimates and Microclimates

Microclimates can be confused with macroclimates, but it is important to understand the difference between the two.

There are five main classifications of macroclimate:

• Tropical
• Dry
• Temperate
• Continental
• Polar

Biomes

There are five major types of biomes:

• Aquatic

• Grassland

• Desert

• Tundra

• Savanna

Climatic factors, like temperature and rainfall, influence biomes.

Microclimates

Microclimates are found within macroclimates and biomes. They occur at much smaller scales, spanning an area of up to 10 kilometres. Let's refer back to the UK's temperate oceanic macroclimate. Within this macroclimate, we can find a range of microclimates – forests, cities, coastal areas, lakes, and valleys.

Microclimate Facts and Examples

In the UK, there are four main types of microclimate – upland areas, coastal regions, forests and urban areas (this one will be discussed in more detail later).

Upland Areas

• Temperature tends to decline with altitude – a drop of 5 to 10°C per every 1000m above sea level. As a result, upland areas experience longer winters and shorter summers. Higher ground is often windy, making winter weather even harsher. Different plants and animals are adapted to these colder, harsher conditions.
• The leeward side of hills and mountains is usually much drier than the windward side. This is because as air descends the slope, it dries and warms. This is known as the Föhn effect.
• However, occasional temperature inversions can make it warmer in upland regions than at sea level. This can happen on clear nights with little wind. During these conditions, valley fog forms, which can last for days in calm conditions.

Coastal Regions

• Coastal climates are more strongly influenced by the sea than by the land. Typically, coastlines are milder during the winter and cooler during summer than regions inland.

• However, short-term variations can be considerable. Coastal regions can be prone to showers, whilst inland areas remain dry. Furthermore, sea fogs can be brought ashore and persist for hours. Daytime heating would cause the fog to clear inland.

• Sea breezes are a key feature of UK coastal regions. These chilly winds are caused by convection currents. Cold air from the sea meets the warm land. The air is heated by the land, so it rises. More cold air from the sea moves in to replace it, forming a sea breeze.

Forests

• Forests in the UK are typically cooler and less windy than surrounding areas – the trees act as a windbreak, and the solar radiation is 'filtered' by the leaves and branches.
• Climatic differences between forests and surrounding areas can vary seasonally depending on if the trees are in leaf.

Urban Microclimates

Urbanisation can disrupt the surface energy balance of an area.

What Causes the UHI?

Constructing buildings close together contributes to the UHI. Buildings that are close together create an insulating effect, trapping heat and making the areas around a building warmer.

The construction itself also affects the UHI. This is because of something known as 'waste heat'. Wasted energy from tools, cars, factories, and construction escapes in the form of heat. Urban areas are typically densely populated, leading to lots of waste heat in a small area.

Areas that have a significant UHI typically experience poor water and air quality due to pollution.

Albedo

The albedo of an urban area plays a part in the UHI.

Darker surfaces, common in urban areas, have a lower albedo. Less heat is reflected away, so more is absorbed and stored by these surfaces. In urban areas, dark surfaces such as pavements and roofs can make up 60% of the area.

How can the UHI be Reduced?

Using green roofs can help reduce the UHI. The plants absorb carbon dioxide and reduce the heat of the surrounding area. A reduction in atmospheric carbon dioxide limits the greenhouse effect, slowing global warming and associated temperature increases.

Using lighter-coloured materials increases the albedo of a surface. This will reflect more sunlight and trap less heat.

I hope that this explains microclimates to you. These localised climates can be affected by topography, soil, vegetation and artificial structures. And now you know for next time to bring an extra layer when you go to the beach!

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