Abstract:
Urbanization in the developing world took place at an unprecedented rate
which outpaced that of the developed world except for few exceptions. Much of the
urban areas of the developing world are in the tropical zone, which has gone through
an inadvertent environmental modification due to increased built density. This
environmental modification due to high built density resulted in an adverse thermal
environment in the urban area which is further exacerbated by global warming due to
climate change. This adverse thermal environment in the city resulted in a muchreported
phenomenon known as Urban Heat Island. An adaptation measure against
Urban Heat Island in the tropical cities of the developing world can be use of the
natural cycle to cool down the overheated urban fabric.
Dhaka is one of the most densely populated cities in the world, where the
juxtaposition of wetlands and built up area coupled together may have an opportunity
for creating a viable and distinct character of its own while addressing the challenges
of inadvertent environmental modification. Increased built density and reduction of
wetlands are making Dhaka’s climate uncomfortable in comparison to its rural
surroundings, resulting increasing number of air-conditioned buildings, which in turn
elevate urban air temperature and consequent energy demand. Thus, urban land use in
Dhaka is directly contributing to Urban Heat Island effect. Coolth produced by urban
wetland can be an adaptive measure against urban heat island in Dhaka. This study
approaches the problem by identifying wetland as existing and potential cool spot and
analyzing their characteristics for cooling efficiency. Remote sensing technique was
used to identify the existing and potential cool spot at surface level for analysis. This
technique applied to analyze the morphology of the wetland as a producer of coolth
with potential to counterbalance for the urban heat. As a part of the study field
campaigns were conducted and environmental variables were recorded on the buffer
area of selected wetlands indicated in the remote sensing study. Evaluations were
undertaken with respect to the design factors such as the orientation of the wetlands,
riparian shading characteristics, urban permeability for the cooling effect, as those
factors affect the cooling intensity produced by the wetland. Through simulation
studies, some aspects are identified which could not be derived from the fieldwork.
They are the effect of differential riparian shading on the wetlands, effects of variable
temperature and relative humidity on the coolth produced by the wetland. Based on
the simulations some urban design recommendations was derived.
The research finding that indicated the relationship between some important
factors like the interdependency between fetch and inversion height to control
inversion layer over the water surface that regulate the urban cooling effect of the
wetland at an urban scale. This relationship informs as to what extent urban wetland
design might impact the thermal environment leading to possible urban microclimatic
cooling. These findings, in turn, might help in the development of certain policy
guidelines for the urban designers and planners to more positively impact the urban
thermal environment.
