A microclimate is a local atmospheric zone where the climate differs from surrounding areas. This term may refer to areas as small as a few square feet, or as large as many square miles. Common areas where microclimates exist are, for example, near bodies of water where the water can cool the local atmosphere and dense urban areas where brick, asphalt, and concrete absorb the sun’s energy, heat up, and reradiate the heat into the air. The latter produces what is known as an urban heat island, which is a kind of microclimate. A contributing factor to microclimate is the slope of an area. South-facing slopes in the Northern Hemisphere and North-facing slopes in the Southern Hemisphere are exposed to direct sunlight more than the opposite slopes and are warmer for longer periods.
Microclimates offer a good opportunity as a small growing region for crops that cannot thrive in other areas. This concept is often used in permaculture-(a system of cultivation intended to maintain permanent agriculture or horticulture by relying on renewable resources and a self-sustaining ecosystem) in northern temperate climates. Microclimates can also be taken advantage of by gardeners who carefully choose and position their plants and flowers. Cities often raise the average temperature by zoning, and some zoning practices may even reduce the severity of winter. Another area microclimates are useful are rooms in a building or other enclosures. Museums utilize microclimates for displays and storage to help preserve natural artifacts that would otherwise be destroyed by the natural elements.
Some cities are more well-known for the microclimates than others. San Francisco has a large microclimate and sub-microclimate system. Due to varied topography and influence from the prevailing summer marine layer, weather conditions can vary greatly from one location to another. The region as a whole, known as the Bay Area, can have a wide range of extremes in temperature. For example, in the Bay Area the average maximum temperature in July is about 64 degrees Fahrenheit at Half Moon Bay on the coast, 87 degrees at Walnut Creek only 25 miles inland, and 95 degrees just 50 miles inland.
Another city known for its microclimatic system is Calgary, Alberta. The most notable differences in this area are between the downtown and river valley regions, and the areas to the north and west. This occurs largely due to an elevation difference of over 1000 feet, but may also be attributed, in part, to the effects of seasonal Chinooks.