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With regard to precipitation gauges in urban areas, the following guidelines are
recommended:
• Gauges should be located in open sites within the city, where the standard exposure criteria can be met (for example, playing fields, open parkland with a low
density of trees, urban airports).
• Gauges should be located in conjunction with wind instruments if a representative exposure for them is found.
• Gauges should not be located on the roofs of buildings unless they are exposed
at a sufficient height to avoid the wind envelope of the building.
• The measurement of snowfall depth should be taken at an open site or, if made at
developed sites, a large spatial sample should be obtained to account for the
inevitable drifting around obstacles. Such sampling should include streets oriented in different directions.
• Dew, ice, and fog precipitation also occurs in cities and can be of significance to
the water budget, especially for certain surfaces. These forms of precipitation
may also be relevant to applications such as plant diseases, insect activity, road
safety, and finding supplementary sources for water resources.
2.4.5 Solar Radiation
Solar radiation data are very useful inputs for several climate variables, such as
atmospheric stability; daytime cloud activity; turbulence statistics; the fluxes of
momentum, heat, and water vapor; determination of mixing height; and pollutant
dispersion and models. The data can also be used to represent daylight levels in
buildings and pedestrian comfort. Adding solar radiation measurements to an automatic station is very simple, relatively inexpensive, and highly recommended.
Solar radiation measurement sites are often located in rural or remote locations
specifically to avoid the aerosol and gaseous pollutants of cities that “contaminate”
their records. For stations located in built-up areas, only incoming solar (global)
radiation is likely to be measured; neither incoming long wave nor any fluxes with
outgoing components are monitored. All short- and long-wave fluxes are affected
by the spatial properties of the atmosphere and the surface of cities, and the same is
true for the net all-wave radiation balance that effectively drives the urban energy
balance.
The placement of solar radiation sensors on the top of high building is a widely
used and preferable practice that avoids horizon obstructions.
The principal exposure requirement for monitoring direct solar radiation is freedom from obstructions to the solar beam at all times and seasons of the year.
Furthermore, the site should be chosen so that the incidence of fog, smoke, and
airborne pollution is as typical as possible for the surrounding area.
On the one hand, incoming solar radiation is a fundamental forcing variable of
urban climate, so its measurement has a high priority in the establishment of an
2 Urban Heat Island Gold Standard and Urban Heat Island Atlas
With regard to precipitation gauges in urban areas, the following guidelines are
recommended:
• Gauges should be located in open sites within the city, where the standard exposure criteria can be met (for example, playing fields, open parkland with a low
density of trees, urban airports).
• Gauges should be located in conjunction with wind instruments if a representative exposure for them is found.
• Gauges should not be located on the roofs of buildings unless they are exposed
at a sufficient height to avoid the wind envelope of the building.
• The measurement of snowfall depth should be taken at an open site or, if made at
developed sites, a large spatial sample should be obtained to account for the
inevitable drifting around obstacles. Such sampling should include streets oriented in different directions.
• Dew, ice, and fog precipitation also occurs in cities and can be of significance to
the water budget, especially for certain surfaces. These forms of precipitation
may also be relevant to applications such as plant diseases, insect activity, road
safety, and finding supplementary sources for water resources.
2.4.5 Solar Radiation
Solar radiation data are very useful inputs for several climate variables, such as
atmospheric stability; daytime cloud activity; turbulence statistics; the fluxes of
momentum, heat, and water vapor; determination of mixing height; and pollutant
dispersion and models. The data can also be used to represent daylight levels in
buildings and pedestrian comfort. Adding solar radiation measurements to an automatic station is very simple, relatively inexpensive, and highly recommended.
Solar radiation measurement sites are often located in rural or remote locations
specifically to avoid the aerosol and gaseous pollutants of cities that “contaminate”
their records. For stations located in built-up areas, only incoming solar (global)
radiation is likely to be measured; neither incoming long wave nor any fluxes with
outgoing components are monitored. All short- and long-wave fluxes are affected
by the spatial properties of the atmosphere and the surface of cities, and the same is
true for the net all-wave radiation balance that effectively drives the urban energy
balance.
The placement of solar radiation sensors on the top of high building is a widely
used and preferable practice that avoids horizon obstructions.
The principal exposure requirement for monitoring direct solar radiation is freedom from obstructions to the solar beam at all times and seasons of the year.
Furthermore, the site should be chosen so that the incidence of fog, smoke, and
airborne pollution is as typical as possible for the surrounding area.
On the one hand, incoming solar radiation is a fundamental forcing variable of
urban climate, so its measurement has a high priority in the establishment of an
2 Urban Heat Island Gold Standard and Urban Heat Island Atlas