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Stories from the field

New action to tackle heatwaves: retrofitting of slums for incoming heat waves

Rafael Díaz-Regañón Jiménez in Viet Nam
Suomen Punainen Risti (Finnish Red Cross)
About the Project
Heat wave is a high impact weather event that can cause major loss of life, and negatively affect health and wellbeing. It is predicted that heat waves will occur with greater frequency and last longer as a result of global climate change. This trend occurs most acutely in urban settings, due to the prevalence of surfaces that retain heat and release it slowly, in what is called the Urban Heat Island (UHI) phenomenon. The effects of UHI are often worse in areas with higher population densities such as informal settlements. Also, high pollution levels and a high humidity in the air heighten the heat wave impact on human health. In Hanoi, Vietnam, where temperatures have risen in recent years, VNRC (Vietnam Red Cross), GRC (German Red Cross) and IMHEN (Vietnam Institute of Meteorology, Hydrology and Climate Change) work together in a Forecast-based Financing (FbF) project to predict the onset of the heat wave, to mobilize funding before the disaster, and to take anticipatory actions (so called “Early Actions”) to reduce its impact on the most vulnerable. This FbF project targets street workers and slum dwellers considered to be among the most vulnerable towards heat waves.

My role as an EU Aid volunteer at the GRC office in Vietnam was to fulfill the need of the VNRC in strengthening its capacities for the FbF project implementation. I contributed to the discussion and understanding between scientists (meteorologists, hydrologists, etc.) and humanitarians required in any FbF project, to translate science and transforming it into action. In this line, I got involved in the development of a new Early Action: retrofitting of informal settlements for incoming heat waves. Furthermore, I carried out the record of experience and lessons learned of different Early Actions simulations through data analysis, reporting of case studies and other monitoring and evaluation reports.

Understanding vulnerability towards heat waves in slums

An extensive Knowledge, Attitudes, and Practices (KAP) survey carried out by the GRC team revealed that during a heat wave, 66% of outdoor workers and slum dwellers in Hanoi experience from 4 to 7 symptoms of heat exhaustion, and that their income is substantially reduced due to increased doctor and healthcare costs. In addition, deaths due to heat are being reported in the last years.

People that live in informal settlements are greatly affected by heat due to different factors. Informal settlements are characterized by poorly built structures, with materials that easily absorb and trap heat and/or with inappropriate insulation (i.e. iron sheets, fibrocement, etc.). Also, they usually don´t have access to cooling systems, which are expensive. Thus, the inhabitants sleep at night in structures that don´t cool down during the night. Some residents resort to some coping mechanisms such as watering their beds and walls in periods of extreme heat.

Also, these neighborhoods are often inhabited by rural migrants, which in turn usually are outdoor workers. This implies that most of slum dwellers are exposed to the sun during the day. Thus, during a period of extreme temperatures, slum dwellers never have a chance to find relief from heat both during the day and night, due to their livelihood (in the streets) and the place they rest in (informal settlement).

Consequently, the presence of slums and of poor material roofs in the wards is heavily weighted in the mapping methodology developed by GRC and VNRC. Since vulnerability and exposure to heat waves greatly varies within a vast city such as Hanoi, this method is designed to discern the 10 most at risk wards for Early Action implementation, by combining three layers of data, differently weighed: vulnerability of the affected population (age, disability, income), the population’s exposure to the heat wave (roof materials, presence of informal settlements), and hotspots (areas with historically higher temperatures).

Developing the Early Action

In one of the identified most at risk wards, an informal settlement was selected for testing the new action. This ward is characterized by its high number of migrant outdoor workers (estimated to more than 3000).

Retrofitting of informal settlements is a measure designed to reduce the inevitable increasing temperatures inside the rooms of the informal settlement during a heat wave day, which results in accumulated heat at night. The objective is to improve the sleeping conditions of people living in informal settlements and poor habitations, and therefore to reduce the occurrence of heat-related symptoms, that can lead to deaths in some extreme cases.  It has two components: shading net and sprinklers. Creating shade can help prevent dehydration and overheating, and therefore to reduce the risk of potentially harmful effects of heat exhaustion, such as heatstroke. On the other hand, the sprinklers further cool down the roof by evaporation by sun exposure during the day.

Working in the informal settlement

In our several visits to the informal settlement we were warmly welcomed by the people that live there, as well as by VNRC. Even though there was some language barrier, I could communicate with all stakeholders thanks to the Vietnamese GRC colleagues. Both the people of the neighborhood as well as the VNRC staff showed acceptance and willingness to implement the idea, with useful feedbacks for a better contextualized action.

At first, my involvement in the preparedness for the action was to participate in various rounds of negotiations between VNRC / GRC staff, and local authorities at different administrative levels. In those meetings we explained the usefulness of the action, and tried to secure access to the informal settlement. Secondly, we carried out a mapping exercise to calculate the areas to be shaded, as well as to plan for obstacles for the nets such as trees or water deposits (see image 1 and 2). At a later stage, I engaged in research on more specific technical aspects of the retrofitting, such as the material of the shading nets or their standing system. This allowed for the preparation of specific shading nets with adequate dimensions, and other materials needed to carry out the Early Action.

To be part in the development of such an innovative action has been a real motivation to my work. I believe it can really reduce risks and consequently bring positive benefits to those who are most vulnerable to heat waves in urban areas, which is a growing concern due to climate change and rapid urbanization.

The retrofitting of informal settlements in Hanoi has not yet been tested since there were some hindrances to secure access to the informal settlement in a short amount of time (also known as “lead time”) required in an FbF project. However, these are particular to Hanoi, and cannot be taken as a norm. In addition, all stakeholders showed a strong interest in the idea. Hence, the idea could be replicated in other urban areas with informal settlements that are significantly affected by heat waves.


Being involved in the development of an action to reduce heat related problems in the most vulnerable has been a great motivation to my work.