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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.
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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