Urban climatology

Urban climatology refers to a specific branch of climatology, it is the branch of climatology concerned with the interactions between urban areas and the atmosphere; the impacts they have on one another; and examines these processes (and responses) at various scales.

History

Luke Howard is considered the father-figure of urban climatology based on his book The Climate of London, which contained continuous daily observations from 1801 to 1841 of wind direction, atmospheric pressure, maximum temperature, and rainfall.^[1]

Urban climatology has gained much momentum in recent centuries based on global industrialization and more importantly, urbanization. The process of urbanization changes the physical surroundings and induces alterations in the energy, moisture, and motion regime near the surface. Most of these alterations may be traced to causal factors such as air pollution; anthropogenic heat; surface waterproofing; thermal properties of the surface materials; and morphology of the surface and its specific three-dimensional geometry—building spacing, height, orientation, vegetative layering, and the overall dimensions and geography of these elements. Other factors that must be considered are relief, nearness to water bodies, size of the city, population density, and land-use distributions.^[2]

Research

In general, cities are warmer than their surroundings, as documented over a century ago by Howard.^[3] They are islands or spots on the broader, more rural surrounding land. Thus, cities produce an urban heat island effect on the spatial distribution of temperatures. The timing of a maximum heat island is followed by a lag shortly after sundown, as urban surfaces, which absorbed and stored daytime heat, retain heat and affect the overlying air. Meantime, rural areas cool at a rapid rate.

A number of energy processes are altered to create warming, and various features lead to those alterations. City size, the morphology of the city, land-use configuration, and the geographic setting (such as relief, elevation, and regional climate) dictate the intensity of the heat island, its geographic extent, its orientation, and its persistence through time.^[4] Individual causes for heat island formation are related to city geometry, air pollution, surface materials, and anthropogenic heat emission. There are two atmosphere layers in an urban environment, besides the planetary boundary layer outside and extending well above the city: (1) The urban boundary layer is due to the spatially integrated heat and moisture exchanges between the city and its overlying air. (2) The surface of the city corresponds to the level of the urban canopy layer. Fluxes across this plane comprise those from individual units, such as roofs, canyon tops, trees, lawns, and roads, integrated over larger land-use divisions (for example, suburbs). The urban heat island effect has been a major focus of urban climatological studies, and in general the effect the urban environment has on local meteorological conditions.

Other Research within the field is focused on Air quality, Radiation Fluxes, Micro-Climates and even issues traditionally associated with architectural design and engineering, such as Wind Engineering.

Climate change

The study of Urban Climatology is strongly linked to research surrounding global climate change: as centres for socio-economic activities, cities produce large amounts of Green House Gases, most notably CO₂ as a consequence of human activities such as transport, development (e.g. concrete production), waste related to heating and cooling requirements etc.

Furthermore globally, cities are said to grow into the 21st century (and beyond) due to the opportunities they present and as a consequence of globalization - as they grow and develop the landscapes in which they inhabit will change so too will the atmosphere resting above them, increasing emissions of GHG's thus contributing to the global green house effect.

Finally, many cities are vulnerable to the projected consequences of climate change (sea level rise, changes in temperature, precipitation, storm frequency) as most develop on or near coast-lines, nearly all produce distinct urban heat islands and atmospheric pollution: as areas in which there is concentrated human habitation these effects potentially will have the largest and most dramatic impact (e.g. France's heat wave in 2003) and thus are a major focus for urban climatology.^[5]

See also

• Urban climate

Bibliography