The past decade has seen a dramatic rise in the number of already hot days getting hotter, and increased frequency of deadly heat waves, defined as prolonged periods of excessive heat.
The global upward trend of extreme heat has contributed to the severity of summer wildfires and drought conditions, and the impacts of heat waves are borne disproportionately by the most vulnerable populations. Factoring in a deadly pandemic, traditional coping mechanisms, including moving vulnerable populations to crowded ‘cooling centres’ may increase the transmission rates of the disease.
In a study in Environmental Research Letters, strategies and a framework to reduce urban vulnerability to extreme heat was discussed. The authors, Wilhelmi and Hayden argue that an interdisciplinary approach is required, including information about weather and climate, the natural and built environment, social processes, interactions with stakeholders and assessment of local community vulnerability.
In considering exposure to extreme heat, the authors identify ‘urban heat islands’ as compared to suburban and rural environments. The temperature gradient may be as high as 10 degrees in denser developments, due to excess heat absorbed and released from denser development. This differential distribution of heat in urban and non-urban neighbourhoods contributes to an increased perception of risk and vulnerability. Vulnerability can be defined not only by the physical proximity to the risk, but by the safety nets that may or may not be available to affected populations.
The C40 Cities Climate Leadership Group, chaired by Mayor Eric Garcetti of Los Angeles have developed a number of best practises to begin to adapt cities to extreme heat:
Measure urban heat and vulnerability to understand the risk. Vulnerable population groups, including the elderly, young children and those with underlying conditions are among the most sensitive to extreme heat. Individuals experiencing homelessness and other marginalized groups may not have equitable access to water, green spaces and air conditioning. In addition to identifying these groups, it’s important to identify the local temperature threshold at which heat becomes a threat.
As an example, in Durban, South Africa, heat vulnerability maps have been created by using information about temperature projections and information regarding urban surfaces (roads and buildings), overlaid with socio-economic data. The result has been a social vulnerability index for sensitivity to heat that can help to guide policy decisions:
Develop a heatwave response plan. Heat vulnerability maps, once in place can guide policy in advance of heat season. Cities are wise to build collaborative partnerships between governments, meteorological agencies, health and emergency departments, the media and other partners to develop a comprehensive response plan. Building local capacity among health-care professionals and communication with the public may raise greater awareness about the heat risk and ways to negotiate it.
Cooling centres and cool routes, along with specialized apps to communicate with citizens may help to raise awareness. Cities such as Paris, Athens and Rotterdam have developed the EXTREMA app to assess heat vulnerability and direct vulnerable individuals to local cooling centres.
Develop long-term plans to reduce the heat threat. Heat mitigation solutions are part of wider urban planning initiatives and may include cool roofs, pavements and road surfaces. Green roofs and walls can also help to reduce temperatures, in addition to increased planting of trees and urban vegetation. Increased vegetation also may help to reduce the risk of flooding.
The NYC Cool Roofs initiative for example provides local jobseekers with valuable training and work experience, that has since been replicated in Spain and South Korea.
Raise awareness of actions to reduce urban heat. Developing information materials with broad appeal may help in achieving secondary benefits such as the creation of jobs, reduced energy costs, improved energy security and air quality, and overall well-being of residents.
Worldwide, heat waves currently impact 200 million people in 350 countries. The Paris Agreement on climate change outlines a target of an overall 1.5 degree reduction, but if this goal is not met, 1.6 billion people may be impacted by urban heat by the 2050s.
Heat waves are predictable hazards. Mitigation actions by cities and governments may help to address and understand heat risk, particularly for those most at risk.