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4. Urban heat Island, UHI types,
atmospheric UHI, UHI intensity
URBAN CLIMATOLOGY
4.1 Urban Heat Island concept
http://weather.msfc.nasa.gov/urban/urban_heat_island.html)
Simplified model – role of natural and anthropogenic factors?
1. Atmospheric Boundary layer Urban Heat Island
2. Atmospheric Canopy Layer Urban Heat Island
3. Surface Urban Heat Island)
4.2 Types of UHI
(Oke 1976)
What variables are measured?
UHI profiles
Reducing Urban Heat Islands: Compendium of Strategies and (Voogt 2000)
UHI types characteristic
Reducing Urban Heat Islands: Compendium of Strategies and (Voogt 2000)
UHI intensity (ΔTu-r)
Conceptual Drawing of the Diurnal Evolution of the Urban Heat
Island during Calm and Clear Conditions (modified from Oke, 1982)
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The size of the city forms the intensity of UHI in general
The size of the city can be characterized via number of inhabitants
There is a relation between maximum UHI intensity (UHImax) and
number of dwellers(P) (van Hove et al. 2011):
UHImax = 2,93 log P – 11,95
For Brno (P = 380 ths.) UHImax = 4,4 °C
UHI intensity (ΔTu-r)
How we can estimate UHI intensity depending on available data?
4.3 Measuring the UHI effect
• „Point“ measurements – standard meteorological stations
• „Point“ measurements – special-purpose automatic stations
• Mobile measurements
• Urban remote sensing
• Urban climate and UHI intensity modelling
All types of measurements also involve three different
components that are hardly to quantify (Lowry 1977):
1. the „backgound“ climate
2. the effects of local climate (topoclimate)
3. the effect of local urbanization
Where are the spatial limits of the urban effect?
Mean daily variations of summer air temperature at urban (M) and rural (P)
stations during clear and calm days in Brno region (left) and daily variation
of urban heat island intensity (ΔT); UHI intensity is expressed as a
difference between mean air temperature at urban and rural stations (right)
UHI Intensity in Brno
UHI – „point“ measurements
Spatial distribution of mean daily air temperature (Tavg), temperature
minimum (Tmin) and intensity of UHI (∆T) in Brno area during clear and
calm days in summer; air temperatures are expressed as deviations from
mean temperature of the study area (c)
Spatial distribution of
meteorological stations in Brno
area (a); selected explanatory
variables (b)
a) b)
c)
AUHI – mobile measurements
8. 7. 2011
31. 1. 2012
Design of measuring routes (a), air temperature
profile along measurement routes (b) and typical
spatial distribution of air temperature in central part
of Brno in early night hours; air temperature is
expressed as deviation (dT) from mean value of the
study area and is typical for clear and calm weather
during summer (c)
a)
b)
c)
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AUHI – mobile measurements
T = f(NDVI)
SUHI – remote sensing
(a) Spatial variability of LST values within the Brno region; LST derived from Landsat thermal
imagery acquired on 15 June 2006. (b) Intensity of surface UHI in Brno region defined as the
difference between urban (M) and rural areas (P); LSTs
A paper by McKitrick & Michaels concludes that half of the global
warming trend from 1980 to 2002 is caused by Urban Heat Island.
4.4 UHI and recent global warming
Urban and rural regions show the
same warming trend.
The greatest difference in temperatures
for the long term averages where across
Russia, Alaska, far north Canada and
Greenland and not where major
urbanisation has occurred.
• UHI intensity in different parts of the wolrd
4.5 Final remarks and questions
• Canopy layer urban heat islands exist in the layer of air
where people live. So why we are taking care about
boundary layer UHIs?
• How do Urban Heat Islands form?
• How we can estimate UHI intensity depending on available data?
• What are the main problems related to UHI?
• Can be there any benefits of UHI?
• Is there any relation to recent global climate change?
4.5 Final remarks and questions
(Strategies to Reduce Urban Heat Islands will
be discussed in the final lecture)