Geoscience Reference
In-Depth Information
Figure 5.5.
Estimated standardized night-time temperature in Lisbon [AND 03]
[ALC 06a]. a) In clear weather and moderate N wind; b) the same
but assuming the inexistence of the city (see text for details)
As shown, this procedure has not only enabled us to draw accurate detailed maps
needed for different purposes, particularly in urban planning [ALC 05; ALC 09], but
it has helped us to understand and to quantify the influence of different non-urban
and urban parameters in near ground air temperature at the mesoclimatic scale. A
particular downscaling based on further measuring and modeling will be presented
in section 5.8.1.
5.7.2.
Frequency of thermal patterns. The Lisbon UHI
The UHI is one of the most interesting features of urban climate and is
considered a negative feature of urban climate in cities with hot summers and in the
present scenarios of urban warming. However, UHI is not a static phenomenon. It is
known to be more intense in calm and clear skies, but each city's thermal pattern has
its own particular spatial and temporal dynamics.
This topic has also been studied in Lisbon, in order to derive results of use to city
planners and stakeholders, by supplying information concerning the frequency of
positive and negative features of the urban climate. The Lisbon mesoscale
climatological network has supplied information continuously over time (since
October 2004) and has helped to establish the frequency of the observed patterns.
The definition of UHI as the difference between the highest temperature in town and
the temperature of the rural area around it [OKE 87] may seem quite simple, but the
methods to compute UHI have to be adapted to each single city and to the available
data. In Lisbon's case it was calculated through the difference between the
temperature recorded at the three measuring points located right at the city center
(Saldanha, Bairro Alto, and Restauradores, Figure 5.4) and the two measuring points
outside the urban perimeter (Monsanto and Carnide, Figure 5.4). Measuring points
Belém and Parque das Nações were not considered once their riverside position
confers them a particular type of climate.
