Heat-Baked Chennai: A Blueprint for Cooling India's Cities

The Urban Heat Island Effect:

1. Growing concern In 2023, the world experienced its hottest year on record, with global temperatures 1.45 degrees Celsius higher than pre-industrial levels, almost touching the 1.5° C limit set in the Paris Agreement.
2. This alarming trend is further exacerbated in cities due to the urban heat island (UHI) effect, where temperatures are significantly higher than surrounding rural areas.
3. Concrete structures, paved roads and a lack of green spaces trap heat and pollutants, creating an "urban bubble", where temperatures are particularly high at night.
4. Regrettably, Chennai has among the lowest percentage of green cover of all the metros in India. The area under the Corporation is greener, with promising initiatives such as “miyawaki forests”.
5. Under high humidity conditions, wet-bulb temperature (indicating the extent to which evaporation can take place and facilitate cooling) of around 38.5° C is considered by the World Health Organization to be “near the limits of human survivability”.

In India, a heatwave is officially declared in coastal areas when the maximum temperatures are over 37° C and 4.5° C above normal.

Chennai's Unique Challenge:

1. The coastal city of Chennai faces an additional challenge because of its high humidity.
2. This reduces the cooling effect of sweating, which can lead to heat stress, exhaustion and even fatal heat strokes.
3. The UHI effect in Chennai further aggravates this problem, adding 2°C to 4°C to the temperatures already increased by the coastal climate.
4. This combination of heat and humidity creates dangerous conditions for residents, especially the vulnerable poor, infants and the elderly.

Heat Action Plans:

1. India has implemented Heat Action Plans (HAPs) at the national, state and district levels to reduce heat-related mortality.
2. These plans focus on early warning systems, shade shelters, drinking water arrangements and adjusted working hours for outdoor workers.
3. These measures, though necessary, are reactive and do not address the root causes of urban heat.

A Proactive Approach: Mitigating the urban heat island effect

1. To effectively deal with the UHI effect, Chennai needs to take proactive measures.
2. The Chennai Metropolitan Development Authority (CMDA) has prepared detailed heat maps to guide local planning and actions.
3. Additionally, the Chennai Climate Action Plan (CCAP) provides various suggestions to mitigate urban heat, although some experts believe it underestimates causal factors and remedial measures.

Green Cover: A Natural Cooling Solution

1. Increasing green cover is an important step in mitigating the UHI effect.
2. Green spaces such as urban forests, parks and tree-lined walkways release moisture that cools the environment.
3. They also influence the local microclimate, reduce air pollution and promote health and well-being.
4. Chennai, which has a lower green cover than other Indian metropolises, could benefit significantly from a well-distributed increase in green spaces.

Energy Efficiency: Reducing Waste Heat

1. Waste heat from air conditioners is another significant contributor to the UHI effect.
2. In Chennai, about 50% of electricity consumption during summer is due to air conditioning.
3. Encouraging the use of energy-efficient air conditioners, better building insulation and ventilation can substantially reduce waste heat and energy consumption, thereby cooling the urban environment.

Additional Measures: A Multi-pronged Approach

1. Other measures to reduce the UHI effect include using permeable pavements, increasing shrubs along pavements, and applying reflective paint to roofs, walls, and roads.
2. Reducing the use of private vehicles and promoting public transport can further reduce urban heat and pollution.

A Model for India: Chennai's Opportunity

1. Chennai, as one of the few cities in India with a Climate Action Plan, has the opportunity to set an example for the rest of the country.
2. By implementing comprehensive measures to reduce the UHI effect, the city can improve liveability for its residents and contribute to a cooler, more sustainable future for India.

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