NIUA Cool Cities Knowledge Hub

WARM CITIES AND HEAT STRESS

Average temperatures in Indian metropolises have risen by upto 0.9 °C in the last few decades . Heat waves, periods of high temperatures (above 40 °C) experienced over continuous days, have become more frequent and intense. Climate change and character of urbanization are driving extreme heat in urban India.

The future could be more disruptive. Temperatures in India could increase by 4.4 °C by 2100 in a worst-case scenario where countries fail to contain their greenhouse emissions reduction targets. Majority of climate change models expect likelihood of severe heat waves to be more pronounced.

Heat waves are intensifying in India

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Cooling with electrical systems
will increase emissions

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URBAN HEAT ISLANDS: LOCAL FACTORS FOR HEAT STRESS

Across the world, cities are heating up twice as fast as the global average because of “urban heat islands” (UN DESA 2018). Urban India is no exception. Heat maps created for select Indian cities confirm hotspots or “heat islands” that experience higher temperatures than surrounding rural or peri-urban zones.

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Dark, heat-absorbing urban surfaces

Concrete, asphalt, glass, and other materials used in buildings and pavements in urban areas have high heat-absorbing properties (also called low albedo) compared to trees and natural ground. 1/3rd of surfaces in an average city globally are hard pavements. Surface temperatures of typical urban surfaces can rise upto 65 °C in summer. Heat absorbed from solar radiation during daytime is emitted at night.

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Lost green and blue cover

Trees, vegetation, and water bodies absorb less heat and cool through evaporation. Contemporary urbanization has overrun vast tracts of natural ground cover and ignored conservation or enhancement of blue-green cover. Indian’s living in metropolises have access to only 2 square meters of open spaces against the 10 square meters recommended by World Health Organization. Unplanned urban development has led to destruction of nearly 2 out of 5 Indian wetlands in the last 30 years.

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Heat trapping urban geometry

Shape, height and positioning of buildings affect exposure to sun of surfaces and wind flows. This, in turn, changes capacity to store or release solar energy. Uniformly tall buildings along narrow streets prevent heat dissipation by reducing wind velocity and frequently, by changing its direction. Taller buildings in mid-to-low rise development face long exposure to sun.

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Anthropogenic heat

Heat is produced and trapped by pollutants from vehicle emissions, warm air exhaust from air conditioners and waste heat from industrial processes. Dispersion of this heat is further slowed by the dense placement of high-rise buildings and narrow road networks.

Updates

Heat Mapping Methodology Workshop

Consecutive record heat waves have made it imperative for urban planners in India to map and prevent exposure to heat stress in the country.

Effects from warming temperatures are particularly harmful in India’s highly populated cities, where preparation of urban heat maps and heat risk assessment in building regulations are essential to tackle urban heat islands.
The National Institute of Urban Affairs (NIUA) and its partners for India Cooling Program, UNEnvironment Programme, and the Ministry of Foreign Affairs of Denmark, organised a workshop in New Delhi with experts from the University of Oxford, UNEP, CEPT Research & Development Foundation, the India Meteorological Department and the Indian Space Research Organisation to discuss a standard methodology for heat mapping in Indian cities.

U20 Manthan: Extreme Heat Planning

NIUA is the technical secretariat for Urban20, a group of cities from the G20 countries aiming to bring forth the unique perspectives of cities to the G20 agenda

by foregrounding critical urban issues Under U20 Manthan, a series of dialogues with experts on urban issues, NIUA, in partnership with United Nations Environment Programme, organized a panel discussion on planning for extreme heat in cities.
The discussions focussed on urban heat islands and urban planning, heat stress related health issues, and, heat resilience planning. Experts from United Nations Environment Programme, National Programme on Climate Change and Human Health, Coalition for Disaster Resilient Infrastructure

DHARA2023: Cooling with Nature

UNEP experts presented the case for river-cooled cities, possible by integrating rivers in district cooling systems,

to minimize cooling costs and emissions at DHARA 2023. Case study of free cooling from River Seine in the Paris District Cooling System was shared with city leaders.
National Institute of Urban Affairs led Driving Holistic Action for Urban Rivers 2023 (DHARA 2023), a two day conclave in Pune for river cities in India. Leaders from 50 Indian river cities, members of National Mission for Clean Ganga established by Ministry of Jal Shakti and Government of India, participated in the conclave.

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