Urban climatology is the study ofurban climate. It is a branch ofclimatology that concerns interactions betweenurban areas and theatmosphere, the effects they have on one another, and the varying spatial and temporal scales at which these processes (and responses) occur.
Luke Howard is considered to have established urban climatology with his bookThe Climate of London, which contained continuous daily observations from 1801 to 1841 ofwind direction,atmospheric pressure, maximumtemperature, andrainfall.[1]
Urban climatology came about as a methodology for studying the results ofindustrialization andurbanization. Constructing cities changes the physical environment and alters energy, moisture, and motion regimes near the surface. Most of these alterations can be traced to causal factors such asair pollution; anthropogenic sources of heat; surfacewaterproofing; 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.[2] Other factors are relief, proximity to water bodies, size of the city, population density, and land-use distributions.[3]
Several factors influence the urbanclimate, including city size, the morphology of the city, land-use configuration, and the geographic setting (such as relief, elevation, andregional climate).[4] Some of the differences between urban and rural climates includeair quality,wind patterns, and changes in rainfall patterns, but one of the most studied is theurban heat island (UHI) effect.[5]
Urban environments, and slightly downwind, are typically warmer than their surroundings, as documented over a century ago by Howard.[6] Urban areas are islands or spots on the broader scale compared with more rural surrounding land. The spatial distribution of temperatures occurs in tandem with temporal changes, which are both causally related to anthropogenic sources.
The urban environment has two atmosphere layers, besides theplanetary boundary layer (PBL) 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 urbancanopy 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 localmeteorological conditions. These are sometimes measured by micronets ormesonets, as well as byEarth observation satellites.
The field also includes the topics ofair quality,radiation fluxes,microclimates and even issues traditionally associated with architectural design and engineering, such aswind engineering. Causes and effects of pollution as understood through urban climatology are becoming more important forurban planning.[7]
Changes in winds andconvection patterns over and around cities impactsprecipitation. Contributing factors are believed to be urban heat island, heightenedsurface roughness, and increasedaerosol concentration.[8]
Urban climatology is strongly linked to research surroundingglobal warming. As centers for socioeconomic activities, cities produce large amounts ofgreenhouse gases (GHGs), most notablyCO2 as a consequence of human activities such as transport, development, waste related to heating and cooling requirements etc.
Globally, cities are expected to grow into the 21st century (and beyond)[9] - as they grow and develop the landscapes in which they inhabit will change so too will the atmosphere resting above them, increasing emissions of GHGs thus contributing to the globalgreenhouse effect.
Finally, many cities are vulnerable to the projectedconsequences of climate change (sea level rise, changes in temperature, precipitation, storm frequency) as most develop on or near coastlines, 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. the2003 European heat wave that especially deadly in France) and thus are a major focus for urban climatology.[10]
Urban climatology impacts decision-making formunicipal planning and policy in regards topollution,[11] extremeheat events, andstormwater modeling.[12]