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Abstract
The hot humid tropics is a region of significant rainfall and abundant solar energy that facilitate high evapotranspiration rates and a rich biodiversity. The region is characterized by its forest landcover that influences the climate by using and dissipating the solar energy and interacting with the water cycle. Many areas of the hot humid tropics are losing this capacity to regulate their typical hydrologic fluxes and surface energy balances due to the extreme land use and land cover change caused by urbanization, thus becoming environments with increased temperatures, disrupted water cycle, degraded water quality and reduced biodiversity.
Green infrastructure is a nature-based solution to mitigate these impacts of urbanization. However, physical limitations of the urban context as well as technical and financial barriers impede to just rely on green infrastructure strategies. Alternatively, the built surfaces of the urban landcover can be adapted to harness the abundant precipitation of the humid tropics for restoring the water energy balances distorted by urban development. One way is the use of rainwater for surface evaporative cooling of conventional buildings, to reduce their heat gains and indoor and outdoor heat transfers from the building envelope while contributing to substantial reduction of stormwater runoff.
This research explores the potential of rainwater use for building surface evaporative cooling (BSEC) from a holistic perspective, integrating criteria from fields such as architecture, building physics, urban climatology and urban hydrology, to verify its relevance as a common strategy for dealing with urban problems in the hot humid tropics such as overheating, flooding and water pollution. Weather influences, hygrothermal performance, effects of radiation and humidity, evaporation rates and water consumption by BSEC in relation to low-rise buildings are measured quantitatively through field experiment, hygrothermal and CFD simulations and water budgeting to determine benefits in thermal performance and the potential demand for rainwater.
The results indicate that, in hot humid tropical environments, the cooling effect of rainfall is not negligible and is produced just by little portion of the precipitation intercepted by the buildings. Also, BSEC strategies effectively diminish urban overheating, generate a significant demand for the precipitation surplus and contribute to considerable runoff reductions. Additionally, the higher humidity from BSEC does not increase thermal discomfort, but the lower surface temperatures are rarely sufficient to achieve outdoor comfortable conditions.