Urban Heat Risk: Protocols for Mapping and Implications for Colombo, Sri Lanka

Global and urban-induced local warming lead to increasing heat risk in cities. The rapid increase in urban population, weak infrastructure, poverty, as well as an ageing population, make the risk more acute in developing cities. However, heat risk is not uniformly distributed and a detailed exploration of the link between urban characteristics and local variations in heat risk is needed to aid targeted mitigation. In this paper, we demonstrate a fine-grained heat risk map using existing data combined with expert opinion in a humid tropical city (Colombo, Sri Lanka) with the objective of highlighting the relative heat risk as a function of physical and socioeconomic conditions across the city. We then simulate the effects of shading and greening on the 'high' heat risk areas, and greening on the 'low' heat risk areas, to show that a combined approach will be needed to reduce risk at 'high' risk areas. In 'low' risk areas, maintaining the green cover is crucial to heat risk reduction. The paper, thus, establishes a protocol for detailed heat risk mapping with existing data and points to the differing importance of shading and greening in different parts of the city, thus, showing where, and to what extent, mitigation actions could be beneficial.