The climate, however, is defined as the average state of atmospheric conditions with their range of variations at a certain place. Determining factors are the geographical position and altitude of a place and its proximity to large water surfaces. The climate is defined by the climatic elements air temperature, humidity, precipitation, air pressure, wind, clouds and radiation.

This definition shows that "the climate" cannot be quantified through a measured variable. In consequence, what can only be measured, monitored and evaluated are single climatic elements. The Academy for Spatial Research and Planning (Akademie für Raumforschung und Landesplanung, ARL) has published meteorological definitions for regional planning as work sheets (SCHIRMER, 1988). Bioclimatology, a science which studies the effects of climate on living organisms, tries to link different climatic elements and give a mostly subjective evaluation. This is the case for thermal stress ("sultriness") as a combination of the elements air temperature, humidity and radiation.

One of the main tasks of climatologists is the synthesis of all climatic elements with simultaneous consideration of their interdependency and of extraneous influences (like type of surface, relief, development structure).

Besides mostly time-consuming and expensive measurements, everyone can watch nature and observe and evaluate climatic conditions. You can observe, for example, trails of smoke as an indicator for the direction of the wind and the thermal stratification of the atmosphere, vegetation and its growth as an indicator for temperature and precipitation as well as ground fog areas as an indicator for local pools of cold air. Another example is the observation of frost damages and local cloud formations.

While the climate in undeveloped areas largely depends on natural conditions and factors, the climate in towns and cities is influenced by buildings and is called the urban climate. The term "urban climate" nowadays also includes changes in the natural composition of the air as a consequence of man-made influences (like corrosive gases and aerosols).

Any kind of building has an influence on the various climatic elements. In climatic terms, large built-up areas differ widely from the surrounding region. The main reasons for the development of a separate urban climate are the far-reaching changes in the heat balance and the local wind field. There is also the fact that the air in the city has a higher pollutant concentration due to domestic fuels, traffic, industry and power plants. The development of a typical urban climate depends predominantly on the size of the city, but also on the orography, the development structure and the percentage of open space.

While some climatic elements differ only slightly from one city district to the other (like solar radiation, precipitation), others differ significantly (like temperature, wind conditions) depending on the heat retaining capacity of the construction materials, the sealing of the soil, a modified water balance as well as waste heat. Local differences can be found around buildings, streets and parks.

Further information on the urban climate can be found in the Urban Planning Climate Manual. Climate Booklet for Urban Development