What are Microclimates?
A microclimate is a small local area where the climate differs from the surrounding area. The term may
refer to areas as small as a few square meters (for example a garden bed) or as large as many square
miles (for example a valley). Microclimates exist, for example, near bodies of water which may cool the
local atmosphere or air, or in town and city areas where brick, concrete, and tarmac absorb the sun's
energy, heat up, and warm the air above: the resulting urban heat island is a kind of microclimate.
Another factor helping to create 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 plants in
parks absorb light and heat in leaves, that a building roof or parking lot just puts heat back into the air.
Some people argue that using of solar collection can mitigate overheating of urban environments by
absorbing sunlight and putting it to work instead of heating the local surface objects.
A microclimate can offer an opportunity as a small growing region for crops that cannot normally survive
in the 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.
A City and Region well Known for Microclimates
San Francisco is a city with microclimates and sub microclimates. Due to the city's varied surfaces and
influence from the prevailing summer sea winds, weather conditions can vary by as much as ten degrees
from block to block.
The region as a whole, known as the Bay Area can have a wide range of extremes in temperature. In the
basins and valleys next to the coast, climate is subject to wide changes within short distances as a result
of the influence of the land surface on the movement of sea 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.
(text adapted from http://en.wikipedia.org/wiki/Microclimate)
The treetops of a high, dense forest can form an almost unbroken surface, which acts in a similar way to
the ground. During the day the tree tops absorb solar radiation, resulting in high temperatures at canopy
level. The temperatures decrease downwards, owing to the shading effect of the trees. Thus, the forest
floor is generally cooler than the canopy and the surrounding countryside. In the Summer this
temperature difference can be as much as 5 degrees Celsius. At night forests retain their heat and are
generally warmer than their surroundings.
The airflow inside a forest is greatly reduced and results in higher humidities. Wind speeds tend to be
very light near the ground, as they are reduced by the canopy of the trees. The effect of rainfall is
difficult to define since it is hard to measure precipitation within a forest. However, deforestation can
cause rainfall to have devastating effects.