2.	Characteristics and Forms of the Urban Climate
2.1 Overview

The development and progression of the weather follow physical laws, which accounts for the frequently quick temporal changes in the state of the atmosphere.

Climate, on the other hand, is defined as the average state of the atmospheric weather conditions and their fluctuations at a specific location. The geographical situation, the elevation of the location, and the distance to large water surfaces are all deciding influences. Climate is described by the climatic elements of air temperature, humidity, precipitation, air pressure, wind, cloudiness, and radiation.

One can see from these conceptual definitions that "the climate" cannot be quantified by specific magnitudes. At most, only measurements, observations, and evaluations related to specific aspects of the climate can be recorded. The Academy for Spatial Research and Land Planning has published meteorological terminology for regional plans (Schirmer, 1988). Bioclimatology (the effects of climate upon humans) has also attempted to connect various climatic elements to one another and to evaluate them subjectively. One such example is the concept of the thermal burden ("heat index"), developed from the combination of air temperature, humidity, and radiation.

One of the main tasks of climatology lies synthesizing all climatic elements under consideration of their respective dependencies and external influences (such as topography, relief, and the built environment).

Notwithstanding frequently time- and cost-intensive measurements, virtually anyone can recognize and in part assess climatic details through simple observations in the natural realm. Examples include the observation of smoke movements as indications of wind direction and atmospheric temperature gradation, the observation of vegetation and its development as gauges for the levels of temperature and precipitation, and noting areas of ground fog cover as an indication of local cold air pockets. Also to be mentioned are the observation of frost damages and local cloud development.

Although climate is largely dependent upon natural features in rural areas, a different climate is produced by the built environment in urban areas – the urban climate. Today, the term "urban climate" also encompasses the change in the natural composition of the air through anthropological influences (air pollution and aerosols).

Every structure has an influence upon the individual climatic elements. Large built-up areas divorce themselves in a climatic sense from their surrounding landscape. The significant causes contributing to the production of a separate urban climate lie in the far-reaching alteration of the heat budget and the local wind field. The city air’s strong saturation with particles from fires, traffic, industry, and powerplants also is a factor. The character of a typical urban climate is first and foremost dependent upon the size of the city, but is also influenced by the topography, urban form, and the proportion of open space.

Although there are elements of the urban climate that differentiate themselves very little based on the location in the city (such as sunlight and precipitation), other climatic elements – affected by the heat retention capacities of buildings, by the soil capping, by altered water budgets, and by heat discharges – show substantial spatial variation (such as temperature and wind patterns). Small spatial variations can be found in areas of buildings, streets, and green spaces.