Summer winds in Funchal and their influence on thermal patterns

Project UrbKlim (POCI/GEO/61148/2004)
Financed by FCT and by FEDER
(Operational Programme for Science and
Innovation 2010)
Cities and Climate Change. What future?
CEG, University of Lisbon, 15-16 May 2008
Summer winds in Funchal and their influence on thermal patterns
1
2
Sérgio da Silva Lopes , António Manuel Saraiva Lopes
Funchal is a small island city, located near the coast and limited in the north by an arch-shaped
mountainous system. In this research an attempt was made to analyse the factors and
characteristics of its climate during summertime, using meteorological data obtained from the
Meteorology Institute network and the Madeira Civil Engineering Laboratory (air temperature
and wind). Satellite Landsat images were also used to generate heat flux models. The urban
climate was studied using data registered at the top of buildings and in urban canyons. Thermal
characteristics of land and sea surfaces were also observed.
The comparison of the wind between the base and the top of the southern slope, in the Funchal
region, revealed that in some anticyclonic circulation situations, which are typical in the summer,
the city is sheltered from the northeast gradient wind due to the presence of the mountain,
topped by the two peaks (Areeiro and Ruivo), which enables the activation of the local
circulation systems in the lower sector of the slope, where the city is located.
The breeze circulation system presents a high occurrence frequency (over 80% of the days
analysed). During the night, the mountain breeze acts towards the city, reinforcing the land
breeze which flows to the sea. During the day, the sea breeze, stronger in the coastal area and
beyond the influence of irregular surfaces, acts in the same direction as the valley breeze, thus
increasing the intensity of rising winds, in the slopes facing south.
Considering, in one hand, the shelter effect created by the mountain, and on the other hand, the
breeze circulation system, which tends to cool down the atmosphere, this research seeks to
verify the heat island effect in Funchal city. It was found that during the daytime period, at the
top of the buildings (in the urban boundary layer) the city is warmer, than the adjacent sea
atmosphere. The largest air temperature differences between land and sea (0,9ºC to 1,3ºC), are
possibly responsible for the sea breeze circulation. In the urban canopy layer, the air
temperature is higher than the periphery to the east and west part of the city. It was found that
this heat island, has an average intensity of 1,5ºC, irrespective of the period of the day.
Keywords: Funchal, urban climate, breeze systems, energy balance, heat island
(1) Madeira Civil Engineering Laboratory ([email protected])
(2) Centre of Geographical Studies of the University of Lisbon