Why cities need action plans to cope with muggier, hotter monsoons

The monsoon, widely anticipated every year in the hope of bringing respite from the searing summer heat, in north Indian cities is fast becoming “more thermally uncomfortable” than the pre-monsoon season, according to recent studies. Simply put, despite ample rain in recent years, the monsoon has not alleviated physical heat discomfort as expected.
Cities end up suffering the most from weather extremes with too many people living and working in cramped and poorly provisioned spaces. But while there is growing awareness of the challenge posed by dry heat and high temperatures, administrative policies are yet to recognise the combined effects of heat and humidity on human health and productivity.
Physiologically, humid heat is more dangerous than dry heat.
It compromises the body’s natural cooling process, preventing sweat from evaporating from the skin. People get dehydrated much faster, going into heat exhaustion, heat stroke and more dangerously, hyperthermia and organ shock.
With humid heat getting more intense in cities, experts say nuanced and localised changes to the emergency response, existing heat mitigation action plans and urban planning are urgently required. The decision-making, they underline, must be informed by solid evidence and detailed vulnerability assessment.
Explaining the variability
A manifestation of the climate crisis and global warming, humidity levels are rising across all Indian cities. However, it is exceptionally high in north India and even the central Deccan, which are usually drier areas, said Avikal Somvanshi, senior programme manager, urban lab at the Centre for Science and Environment (CSE), a Delhi-based green think tank.
In May this year, CSE released a study co-authored by Somvanshi, which compared air and land surface temperatures and relative humidity (RH or the amount of moisture in the air compared to what the air can hold) in Delhi, Mumbai, Kolkata, Hyderabad, Bengaluru and Chennai in the last 10 summers with an average of 2001-10. Researchers found that there was an average increase of 7% in RH in the otherwise humid cities of Mumbai and Kolkata, while Chennai experienced a 5% increase. Even though the three cities remained over 25% more humid than Delhi and Hyderabad, the latter two cities, located in one of the driest climatic zones of India, were experiencing something unusual. On average, humidity increased in Hyderabad and Delhi by 10% and 8%, respectively, compared to the 2001-10 period.
Consequently, it found that in the last 10 summers, monsoon has become even hotter in Delhi, Mumbai and Kolkata, while in Chennai, the marginal cooling noted with monsoon has disappeared. Monsoon is still a bit cooler than pre-monsoon in Bengaluru and Hyderabad, but the magnitude of cooling has reduced.
Another study by IPE-Global (an international development consultancy) and EsriIndia (GIS solution provider) released in August this year found that in India, monsoon months of June, July, August, and September are witnessing “extended summer-like conditions except on non-rainy days.” Also, these trends are particularly prevalent in districts located in plains and hilly regions, proving to have “deterrent impacts on lives, livelihoods and economic sectors.”
What explains this climate variability? As the Arabian Sea and the Bay of Bengal warm, more moisture is pushed into the land, said Rajib Chattopadhyay, senior scientist at India Meteorological Department (IMD), Pune. “It is a hydrological cycle — if there is enough moisture, it is supposed to precipitate out. But if the mean temperature is high because of the warming and other local factors are not favourable, it can’t precipitate out resulting in high levels of local moisture (build-up),” he explained.
If the moisture is not reduced, night temperature will remain high, which in turn, keeps the next day’s maximum elevated. “In humans, the metabolic rate is affected if the body cannot rest adequately at night because it is too hot… Urban heat islands or any other such source of heat increase temperature. Just as cloudy nights are uncomfortable because heat is trapped,” Chattopadhyay added.
But what must cities then do to build resilience against muggy heat?
Measuring humid heat
To start with, experts seek more evidence. “We cannot formulate a policy and issue warnings on humid heat-related stress unless we have adequate data, results and thresholds,” said MN Rajeevan, former secretary to the Union ministry of earth sciences.
IMD, which issues heatwave warnings, launched the “heat index” on an experimental basis last year. It records the impact of humidity on high temperatures giving a measure of feels-like temperature to estimate human discomfort through colour codes – green being comfortable at less than 35 degrees Celsius (°C) and red at greater than 55°C, which is dangerously high. The equation used is similar to the one deployed by the US’s National Weather Service and National Oceanic and Atmospheric Administration.
“We issue heatwave warnings based on night and day temperature, wind and humidity levels. We also give a heat index in colour-coded categories, which can be used to assess the degree of discomfort and severity of heat impacts. However, as the heat index is not validated with the actual data on morbidity and mortality, we cannot use it to issue heatwave alerts,” said Mrutyunjaya Mohapatra, director general at IMD.
Another form of measuring the impact of humid heat on the body is wet bulb temperature.
Wet bulb temperature is read by a thermometer that is covered in a wet cloth. But when the air is saturated with as much moisture as it can hold under the ambient conditions, it prevents evaporation. Wet bulb temperature, therefore, measures how much an object can possibly cool down.
From a health perspective, wet bulb temperature reflects whether the human body can sweat or not. People sweat in order to regulate their body temperature, and evaporation of their sweat helps release heat and lower the temperature. The higher the humidity, the less a person can sweat and, consequently, the lower the amount of heat the body can release.
Mapping vulnerability
Translating the meteorological information into action plans ranging from emergency response to long-term mitigation and adaptation requires an understanding of local context and vulnerability assessment.
Last year, the Delhi-based Centre for Policy Research reviewed 37 heat action plans (HAPS) published by various Indian states, districts and cities between 2016 and 2022 to find that these documents mostly focussed on dry extreme heat. Only 10 out of 37 of these plans established locally defined temperature thresholds, though it was unclear whether they took humidity, hot nights, and duration of continuous heat into account to declare a heatwave.
Also, very few of them based their action on vulnerability assessments, and took “homogenised characterisation of vulnerable groups as outlined in NDMA guidelines, which results in a high risk of misdirected efforts,” the report said.
As susceptibilities to humid heat waves vary among different age groups, genders, and living and working conditions of exposed individuals, action should be prioritised accordingly, said Abinash Mohanty. head of climate change and sustainability, practice at IPE Global and expert reviewer of the Intergovernmental Panel on Climate Change’s Sixth Assessment Report.
Using such a heat index, he said, we must map the critical vulnerabilities with the help of a heat-risk observatory (HRO). HRO is a risk-informed decision-making toolkit for policymakers in the National Resilience Programme. It looks at acute heat risks at a hyper-granular level to prepare action plans to deal with extremities such as urban heat islands, water stress, crop loss, vector-borne diseases, biodiversity collapse, and ecosystem collapse. HRO can be used to alert people about the potential health risks of, say, working or playing outdoors for an extended time, said Mohanty.
Along with the Brihanmumbai Municipal Corporation and UNDP, IPE Global and Esri India are working on a Multi-Hazard Risk Atlas for Mumbai that will include the components of HRO. “This can help reduce the underestimation of economic, social, health, and financial losses due to heat stress,” he said.
The problem with heat stress diagnosis is that it is done after excluding all other causes, said Dr Dileep Mavlankar, former director of the Indian Institute of Public Health in Gandhinagar who assisted in drafting Ahmedabad’s — and India’s first — heat action plan in 2013.
“This requires a re-education of medical professionals. Better surveillance and more physiological studies must be undertaken by medical colleges because most poor (and vulnerable) people end up here for treatment,” he said.
Policy response
North Indians might be accustomed to hot weather, but extremely humid heat necessitates different coping mechanisms. For example, desert coolers, which have been the most effective and affordable cooling appliance in the north, do not work well in sultry weather conditions. Those who can afford them, install air-conditioners to weather-proof their living environment even as it puts extra strain on the power grid. However, a large majority of citizens do not have that luxury.
While addressing economic inequality remains a larger question, experts suggest a host of short and long-term measures which can help lessen the impact of such heat hazards.
Cooling centres can be created as an emergency response. Public spaces such as bus stands and train stations can serve as temporary relief zones during heat waves, providing respite to those working outdoors or commuting, said Umamaheshwaran Rajasekar, advisor, urban resilience at the Coalition for Disaster Resilient Infrastructure.
Humidity levels are a result of a lot of factors, most of which are uncontrollable. “But we can always control how much heat we are releasing into the atmosphere and that heat is not transmitted from one place to the other,” said Mohanty. ACs, for example, have a negative impact they cool the interiors but warm the outdoors. The use of glass and steel in construction heats up buildings.
To lower temperatures, a few Indian cities are experimenting with cool roofs or the use of highly reflective paint that reduces heat absorption and electricity consumption. The Eco Niwas Samhita, an energy conservation code prepared by the Bureau of Energy Efficiency, promotes cooling in residential buildings. Telangana has a cool roof policy that sets targets for Hyderabad and surrounding areas.
“But cool roofing and passive ventilation are effective when incorporated early in the design process, rather than being retrofitted later,” said Rajasekar. He pushes for modification of building bylaws to account for climate variability and the urban heat island effect; maintaining green and blue cover within cities; and using IoT (Internet of things) to monitor microclimates and indoor heat indices.
Building resilience against humid heat also requires public awareness. Mohanty suggests the appointment of heat-risk officers to communicate with citizens. “Also, attributional factors such as what heat does to family health budgets and labour productivity must be put in the public domain.”
Advocacy must also include sharing information on traditional cooling methods such as clothing and dietary practices in use in the already hot and humid parts of India. “If you eat something easy to digest – such as the summer diets in the coastal regions – then automatically, the body’s internal heat generation is reduced,” said Vidhya Venugopal, professor and country director at NIHR Global Health Research Centre on Non-Communicable Diseases and Environmental Change and Sri Ramachandra Institute of Higher Education and Research, Chennai.
Institutionalising the effort
As for all plans and policies, implementation of action against heat hazards requires navigating the complex governance structures that exist in Indian cities. Also, without adequate mandates, it is difficult to regulate or demand action. “It has to start with IMD to formalise the alert system. Government agencies do not react to policies unless they are told in writing what they have to do,” said Somvanshi.
If devised well, such protocols could be a template for the fast-warming cities. No place in the world is experiencing the escalation in humid heat levels as India and the Arabian countries, pointed out Somvanshi. “We are the first responders to this new climate crisis. We must devise policies so when Europe and the Mediterranean region start experiencing it, they will probably look at us to understand how we dealt with it.”