The microclimatic effect of
vegetation in urban squares.
Cases studies in Milan, Italy.
by Gianni
Scudo
Santa Maria delle Crociate place now Piazza
Paolo VI in MIlan
Most
studies on vegetation influence in outdoor thermal conditions have been carried out
focusing mainly on large green areas. The effect of vegetation in small areas, like urban
squares and streets are much less known even if in most cities their effect in
microclimate modification is important. The present work shows the first results on
measured data collected in four urban squares at Milan.
The "Cooling" effect of large parks and green belts in modifying urban heat
island has been measured and evaluated by many authors. There is a large agreement on air
temperature difference of about 2-3 °C between the interior of large green areas
(let’s say larger than 50 hectars) and the immediately surrounding built up areas.
Very little work has been done on the cooling effect of smaller green areas (up to 3
hectars which is a neighbourhood park or large "square" dimensions) although
very often their influence on surrounding built areas is mentioned in current outdoor
space bioclimatic approach.
This work is a first empirical step to study the effect of vegetation on the microclimate
of public spaces in Milano. The programme is to analyse streets and squares which actually
are often reduced to a polluted place to pass quickly through but which were built and
used up till few decades ago as a "domestic environment" a sort of "house
without roof"
We started with squares. The criteria of the samples choice was to have two small squares
in the central area and two larger squares in the XIX century expansion.
The "cool pocket" effect of vegetation in squares is quite consistent mainly
when tree canopy layer is continuous and square space is "closed" by surrounding
buildings (i.e. the English "green square").
In Milano climate the main effect of vegetation is due to to solar control (obstructed,
reflected and absorbed radiation) which strongly modifies the thermal radiant budget and
therefore the environmental variables of thermal comfort.
Iso budget in Santa
Maria delle Crociate place (now Piazza Paolo VI), July at 1.30 p.m.
The
empirical work done up till now did not afford methodological approach which is anyway
necessary to generalize case studies and to develop guidelines for bioclimatically
conscious outdoor space design.
Microclimatic methodologies developed by meteorological science are often too complex and
anyway not suitable as design tools. Landscape and Bioclimatic approaches to outdoor space
design are not quite well developed from a design tool point of view.
The approach we are goung to utilise in a near future is based on a method under
development by R. Serra Research Group at the UPC-ETSAB which allows to determine the
parameters of the square - vegetation system in term of interaction between microclimate
and conventional spaces variables (location, space, spatial limits).
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