Surface fraction as a variable for urban heat island Amelioration in Colombo

Rapid urbanization has resulted in the change of land use and thus land cover from rural natural, pervious green surfaces to impervious urban land. It is identified as a key reason for microclimatic changes that create the Urban Heat Island (UHI) phenomenon that effect many cities. Although, the planning parameters for Colombo, Sri Lanka do specify the building to non-built surface fraction, it does not define the nature of the non-built areas. It is also deemed that such planning and building regulations are not based on any overall climatic goals for the city. In this context, the need is to quantify urban parameters that can be controlled by urban design. This study explores the effect of the building surface fraction, impervious surface fraction, and pervious surface fraction of an urban block, as a strategy for UHI amelioration in Colombo. The range of the combinations of the above are limited to the range defined by the Local Climate Zone (LCZ) classification system. It is further focussed on the predominant LCZs of Colombo, LCZ3 - Compact Lowrise and LCZ2 – Compact Midrise. The study uses the computer simulation software ENVI-met to model the existing as well as the modelled surface fraction of a particular urban block, in Colombo. Results and Analysis will discuss the comparative implications of the changing surface cover on the UHI mitigation possibility in warm humid Colomb