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VII. Spatio-temporal variability of other
meteorological elements in urban areas
URBAN CLIMATOLOGY
7.1 Urban
climate effects
7.2 Humidity in urban areas
• Spatial and temporal variability of air humidity in urban areas
is the result of evapo-transpiration, condensation and
advection processes.
There are several positive and negative feedbacks.
• Higher temperature -> higher intensity of evapotranspiration
(that is however low due to lack of vegetation
• No consumption of latent heat -> rising temperature
• Fast runoff -> les intensity of evaporation
• Urban dry island
7.3 Wind field in urban environment
Wind filed in urban environment is modified due to mechanical
(left figure) and thermal (right figure) effects
Wind field modification in
urban environment in vertical
(above) and horizontal
direction (below)
Local circulation resulting from
temperature differences between
rural and urban areas (modified
after Munn 1968)
warmercooler
Intensity of turbulence
The ratio between maximum daily wind speed and mean daily wind
speed may be used as a simple measure of intensity of turbulence.
The ratio is clearly higher at the urban station.
Intensity of turbulence
Daily variation of the intensity of turbulence defined as a ratio of maximum wind speed
(Fmax) and mean wind speed (Fprum) at urban and rural stations, period 2005–2011
Daily variation of mean maximum wind speed at Tuřany and Žabovřesky stations in the period
2005–2011
urban
rural
rural
urban
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Wind field modification
Modification of wind speed near obstacles calculated using WAsP model –
an example for for high-rise buildings (60 m) at Šumavská str. a) study
area (black – buildings, green – roughness, red – altitude); b) mean wind
speed near buildings for NW wind direction; c) relative reduction of mean
wind speed near buildings for NW wind direction
7.X Final remarks and questions
1. How does the vegetation in urban areas influence humidity?
2. What can be the most important negative effects of wind
field modification in urban areas?