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June is but to finish and the mercury is touching 49°! Know what the climate division mentioned about ‘warmth hunter’ – extra heatwave alert issued in Delhi, UP, Bihar, IMD warns climate replace

Temperatures are usually not the one factor rising in these cities The Heart for Science and Setting (CSE) has completed a examine on 6 cities of the nation – Delhi, Bangalore, Chennai, Hyderabad, Kolkata and Mumbai. This examine has discovered that not solely the temperature is rising, however the wind, floor floor temperature and humidity collectively are pushing these cities in the direction of insufferable warmth. A warmth index of 41 levels is taken into account deadly for folks. In response to Anumita Raichaudhuri, Government Director of CSE, in view of this variation, there’s a must make a warmth administration plan for day and night time. It is necessary that emergency measures are taken throughout warmth wave. A long run plan needs to be made to scale back this outbreak. For this, there’s a want to extend inexperienced space and water our bodies, enhance the thermal consolation of buildings, scale back the warmth emitted from autos, concentrate on AC and trade. The examine has in contrast between January 2001 and April 2024.

Urban heat island effect hits Indian cities harder by night—make that 60 per cent hotter

ccording to an analysis by the Centre for Science and Environment (CSE), New Delhi Delhi, cities are not cooling down at night like they used to in 2001–10 because they have 'become more concretised in the last two decades', contributing to a rise in heat stress. The analysis said that while increasing green cover can moderate daytime heat, it is ineffective for arresting nighttime heat. According to the World Resources Institute (WRI) India Ross Center, seven out of 10 people around the world are projected to be living in urban areas by 2050. While about 90 per cent of the growth is expected to happen in the Global South, a significant fraction of this will occur in India, it said.

What Is Causing Severe Heatwaves In Delhi, Mumbai, Other Big Cities? New Study Explains Factors Causing Heat Stress

An analysis of six megacities in India - Delhi, Mumbai, Kolkata, Hyderabad, Bengaluru, and Chennai - revealed that nighttime temperatures are not cooling down at the rate they used to during 2001-10. The analysis also highlighted the factors causing increased heat stress in urban cities.\"Increasing relative humidity across all climate zones has worsened the heat index (combination of air temperature and relative humidity) and heat stress in every city,\" said a trend-analysis report released by the Centre for Science and Environment. The study was conducted by the CSE between the summers of January 2001 and April 2024 is heat stress?The CSE explained in its analysis that the heat stress is not just about rising temperatures. \"It is a deadly combination of air temperature, land surface temperature and relative humidity that leads to acute thermal discomfort and heat stress in cities,\" the report said has made heat stress worse?1. Rising Humidity: As per the report, the increase in relative humidity in all zones \"has made heat stress worse in warm-humid and moderate climate zones\". This increase has also \"nullified the fall in air temperatures in composite and hot-dry climate zones, especially during monsoons\".The report highlighted the city-wise trends and added that the increased humidity in Delhi and Hyderabad, which are located in climate zones known for the driest and harshest summers, \"somewhat nullifies their marginal drop in ambient air temperatures\".2. Spike in built-up area: An increase in the built-up area in cities is another factor contributing to the urban heat stress. \"All megacities have become more concretised in the last two decades; this has contributed to the rise in heat stress,\" the report said added that though an increase in green cover can moderate day-time heat, it is not that effective in arresting night-time heat.\"Built-up area has increased from 31.4 per cent in 2003 to 38.2 per cent in 2022. Green cover has increased from 32.6 per cent in 2003 to 44.2 per cent in 2022. An increase in green cover shows the impact on daytime temperatures, but it has had no impact on night-time temperatures and the increasing heat index,\" the CSE said in its analysis in the other four cities, increased humidity intensifies the heat stress temperatures in 6 citiesThe analysis revealed that Mumbai, Kolkata, Bengaluru, and Chennai have seen an increase in air temperature, while Delhi and Hyderabad appear to be defying the trend summer-time average ambient temperature has risen by about 0.5°C in Mumbai, Bengaluru and Chennai compared to 2001-10. Kolkata's decadal average is also up by 0.2°C, the CSE study added, Delhi and Hyderabad registered \"lower decadal average compared to 2001-10\". It added that the decadal summer-time average for Delhi is down by 0.6°C and for Hyderabad, by 0.9°C, compared to 2001-10 does heat stress affect humans?The combination of high heat and humidity may compromise the \"human body's main cooling mechanism\" – that is sweating. Avikal Somvanshi, senior programme manager, Urban Lab, CSE, explained that the evaporation of sweat from the skin cools bodies, but higher humidity levels limit this natural cooling.\"As a result, people can suffer heat stress and illness, and the consequences can even be fatal even at much lower ambient temperatures. Interestingly, nighttime temperature remains elevated in cities,\" said Somvanshi hotter nights ahead?The analysis further showed that the six big cities are not cooling down at night at the rate they used to during 2001-10. Only Kolkata, among other metro cities, cools down at night at the same rate as in 2001-10, the expert from CSE, said hot nights are as dangerous as mid-day peak temperatures. She cited a study published in the Lancet Planetary Health to inform that the \"risk of death from excessively hot nights would increase nearly six-fold in future\".\"This prediction is much higher than the mortality risk from daily average warming suggested by climate change models,\" Somvanshi added CSE study further revealed that the \"urban heat island effect\" is stronger at night. It said that at night, the peri-urban area cools down by 12.2°C, while the city core cools down by only 8.5°C. \"Thus, the city core is cooling down 3.8°C less than its peri-urban areas,\" it added. The study noted that March-April of 2024 was 3°C cooler than the average of 2014-23 is the urban heat island effect?The new analysis by the CSE showed that an unprecedented heat wave has been gripping Indian cities this summer, worsening the urban heat island effect \"urban heat island\" effect happens when built-up areas in urban regions trap heat, reduce green cover, cause congestion, absorb heat, and generate additional heat from human activities said the urban heat island effect can add 2°C to local warming, reducing the adaptive capacity of cities and increasing the risks.\"This is due to reduced ventilation, heat-trapping by closely spaced tall buildings, heat generated directly from human activities, heat-absorbing properties of concrete and urban building materials, and limited vegetation,\" the analysis explained.

Heat Wave: बढ़ते शहरीकरण, उमस से भारत के शहरों में जानलेवा बनी गर्मी, CSE की रिपोर्ट में अहम खुलासा

बढ़ते शहरीकरण और उमस के चलते भारत के महानगरों में गर्मी का तनाव बढ़ रहा है और यह बर्दाश्त के बाहर हो रहा है। सेंटर फॉर साइंस एंड एनवायरमेंट (सीएसई) की ताजा रिपोर्ट में दावा किया गया है कि एक दशक की तुलना में अब भारतीय महानगरों में रात का तापमान ज्यादा नहीं गिर रहा है, जिसके चलते रातें ठंडी नहीं हो रही हैं। सीएसई ने जनवरी 2001 से लेकर अप्रैल 2024 तक देश के छह महानगरों दिल्ली, मुंबई, कोलकाता, हैदराबाद, बंगलूरू और चेन्नई के हवा के तापमान, सतह के तापमान और उमस के स्तर में आए बदलावों की समीक्षा की है।

Delhi heatwave: How are residents coping with extreme weather?

Scorching temperatures in Delhi have forced authorities to issue a red alert for the sweeping heatwave that has disrupted routine activities in the national capital. Rohit Garg, a 24-year-old gig worker, was admitted to the capital’s Safdarjung hospital when his body temperature rose and he began shivering. Delivering food parcels on his two-wheeler in the blistering heat enveloping Delhi had taken its toll, and he fainted at his last stop. “His sugar level dropped, and he suffered from severe dehydration. We had to put him through rehydration therapy as he suffered a heat stroke,” Ashutosh Singh, a doctor, told DW. Jagan Das, a construction worker, has just recovered from a local hospital stay of four days, where he was on intravenous fluid. “I was dehydrated and am fortunate to survive. Working shifts of 10 hours in high temperatures put me down,” Das told DW. Sizzling Delhi With Delhi continuing to reel under scorching heat, arrangements are in place at several hospitals to treat patients suffering from heat-related health problems such as exhaustion and stroke. Some have set up dedicated units to treat patients suffering from heat-related health problems. The Delhi government has asked hospitals to initiate a heat-relief action plan and ensure preparedness to deal with heat-related incidents (HRIs). In the last fortnight, 10-15 per cent more heat-related patients have come to OPD and about 10 per cent to the emergency department. “Our hospital staff is being sensitized for quick pick up of diagnosis and we are ready with rehydration therapy, depending on the severity of heat stroke patients,” Sumit Ray, medical director of Holy Family Hospital, told DW. With no respite from the heat expected anytime soon, the India Meteorological Department issued a “red alert” about severe conditions in the national capital. Najafgarh in south Delhi recorded a maximum temperature of 47.8°C (118°F), the highest of the season so far. The Delhi government directed the schools that have not closed for summer vacations to do so with immediate effect. Public parks and markets are reporting thin attendance, and zoo authorities have begun to introduce preventive measures such as hosing down animals and installing water coolers in enclosures. Extreme heat affects poor However, no help is forthcoming for Delhi’s outdoor workers and low-income households, even though rising temperatures can pose serious health risks. “We bear the brunt of the heat wave—dehydration and heatstroke—almost daily, and there is an absence of basic facilities from the scorching sun,” Meena Devi, a daily construction worker, told DW. Many contractors fail to provide essential requirements to their laborers. Lack of access to adequate healthcare facilities and unsafe working conditions pose significant risks to workers’ well-being. “It is difficult to work, but if I don’t, I won’t get an income,” said Devi, with her head and face covered by a scarf. She added that the heat also takes a toll on her two young children, whom she brings to the site. Last week, the municipal authorities stopped the water supply, and many people had to make a tortuous walk a kilometre away to fetch water from trolleys filled with buckets. The poor and the homeless, who work or sleep outdoors, have been the worst affected by this climate. Many resort to makeshift measures, such as using tarpaulin and seeking shade near trees and parks, to lessen the impact of extreme heat. “The number of heat wave days has increased. It is not just day temperature that we have to battle, but night temperatures have also been high,” Hiralal Paswan, a rag picker, told DW. Coping with extreme heat With temperatures spiking to 50°C, even election candidates and party workers take a break from outdoor campaigning from noon to 3 pm amid the ongoing election campaign. “When the sun is at its fiercest at this time, our door-to-door campaigning, where workers distribute pamphlets, paste stickers, and tell voters about party symbols, come to a brief halt,” Raghu Jain, a political party activist, told DW. “But it is only a temporary reprieve. There is heat stress on the body, and several workers have fallen ill due to sheer exhaustion,” added Jain. Also Read | Climate finance programme funnelling billions of dollars back to rich countries Measuring the impact of heat can be difficult, and estimates of the number of deaths attributed to scorching temperatures vary from a few hundred to a thousand a year. Dense concentrations of buildings and paved surfaces amplify the temperatures, especially in areas with little tree cover or green space, creating heat islands where poor and minority neighborhoods often bear the brunt. Experts point out that if current warming trends continued, wet bulb temperatures, a measure of heat and humidity indicating the point when the body can no longer cool itself, would be so high that people directly exposed for six hours or more would find it difficult to survive. “A large proportion of our population is highly vulnerable to heat waves due to the possession of fewer household amenities as well literacy rates literacy and access to water and sanitation,” Sunita Narain, director of the Centre for Science and Environment, told DW.

High humidity adds to city’s heat stress, reveals CSE study

New Delhi: A study by Centre for Science and Environment (CSE) has noted that an unprecedented heatwave has been enveloping Indian cities, worsening the urban heat island effect. The analysis showed that the heat stress is not just about rising temperatures but also a deadly combination of air temperature, land surface temperature and relative humidity that leads to acute thermal discomfort in cities, including the national capital. The analysis, for which CSE has been making assessments since 2001, covered major cities like Delhi, Mumbai, Chennai, Kolkata, Bengaluru and Hyderabad. It focused on the trends in day-and night-time temperature, humidity levels, seasonal variations, land surface temperature and built-up area. The study found that while the average temperatures for Delhi in March-April were lesser, the humidity levels were high, which worsened the heat stress. These two months were three degrees cooler than the average of 2014-23. “Delhi’s summer-time has registered a 0.6 degree Celsius lower decadal average ambient air temperature, but relative humidity has increased by 8% between 2001-10 and 2014-23. High humidity is responsible for adding to heat stress… An average 3.3°C of heat stress is being added,” the study found. The cities are also not cooling down at night, CSE added. “Diurnal cooling down of land surface temperature between day and night time is down by 9%,” stated the study. It added that the urban heat island phenomena was stronger at night. According to the report, at night, the peri-urban area cools down by 12.2 degrees Celsius, while the city core cools down by only 8.5 degrees. The analysis held a direct correlation between an increase in built-up area and the rise in urban heat stress. “The built-up area has increased from 31.4% in 2003 to 38.2% in 2022. The green cover has increased from 32.6% in 2003 to 44.2% in 2022. The increase in green cover shows impact on daytime temperatures, but it has had no impact on night-time temperatures and the increasing heat index,” the report stated. The study also pointed out that monsoons are getting more “thermally unconformable” because the average heat index during monsoons is 9.4 degrees Celsius more than pre-monsoons. The study defined summer as the period from March to August and further divided it into pre-monsoon (March-May) and monsoon (June-August). According to CSE, while cities in warm-humid and moderate climate zones have seen an increase in their temperatures, those in composite and hot-dry climate zones witnessed a decline. Overall, the ambient air temperature changed by less than 0.5°C between 2001-10 and 2014-23.

Hotter nights and muggy days: Why Delhi has been feeling warmer over the years

Why have you been feeling hotter on summer days? An analysis by the Centre for Science and Environment (CSE) — which used temperature and humidity data from the IMD — shows there has been an increase in humidity levels over the past 10 summers, how land surface temperatures are cooling down to a smaller extent at night, and how built-up area has increased. On Monday, the city recorded heatwave conditions with a maximum temperature of 45.1 degrees Celsius. The highest maximum temperature recorded during the day was 48.8 degrees in Northwest Delhi’s Mungeshpur. Heatwave conditions are set to persist till Thursday, going by the India Meteorological Department (IMD) forecast. According to the CSE analysis, Delhi’s ambient air temperature “shows little change” over the past 10 summers compared to the 2001-2010 decade. However, the “nature of heat is changing” with a significant increase in relative humidity over the past 10 summers. The analysis considered the months from March to August as summer months, divided into pre-monsoon (March to May) and monsoon (June to August). The last 10 summers (2014-23) in Delhi have been 8% more humid on average compared to the average relative humidity from 2001-2010. While the average relative humidity for the summers from 2001 to 2010 was 52.5%, in the summer of 2023, this was as high as 60.9%. Similarly, in 2020, it was 61.4%, while it was 57.3% in 2021, and 53.5% in 2022, going by the analysis. The analysis explains that the combination of high heat and humidity can compromise sweating — the body’s main cooling mechanism. “The evaporation of sweat from the skin cools our bodies, but higher humidity levels limit this natural cooling. As a result, people can suffer heat stress and illness, and the consequences can even be fatal…” it added. The analysis also considered the ‘heat index,’ a measure of how hot it feels when humidity and temperature are both factored in. “It is considered that a heat index of 41 degrees Celsius is dangerous to human health,” the analysis noted, adding that in the summer of 2023, Delhi recorded 14 days when the daily average heat index crossed the 41-degree mark. The analysis also said Delhi is “not cooling down at night” – during the summers of 2001-10, the land surface temperature would drop by 12.3 degrees on average from the daytime peak to the nighttime low. Over the past decade, 2014-23, this nighttime cooling has fallen to an average of 11.2 degrees Celsius, and has been even lower in recent years – 9.8 degrees in 2023. “Hot nights are as dangerous as midday peak temperatures – people get little chance to recover from daytime heat if temperatures remain high overnight,” it explained, adding that the city’s ‘core,’ with the higher built-up area and population, is 2.9 degrees Celsius hotter than its peripheries. The analysis used satellite imagery to determine that the city’s built-up area has increased from 467.8 sq km in 2003 to 568.9 sq km in 2022.

Dark & warm: Nights in India's megacities not cooling down, says CSE report

India’s megacities are not cooling down even during nights in the summer months, according to a report. These cities also face significant heat stress during the Monsoon. In fact, the heat index (HI) in major metro cities in the country has majorly risen since 2010 compared to a decade earlier, a latest report by the Centre for Science and Environment (CSE) pointed out. Concretisation, rising humidity along with global warming have played a role in increasing the heat index of highly populated and urban cities. The annual mean land surface air temperature averaged over India during 2023 was 0.65 degree Celsius above the long-term average (1981-2003), the CSE report said. The report has studied the HI of Delhi, Mumbai, Hyderabad, Bengaluru, Kolkata and Chennai. HI is a measure of how hot it really feels when humidity is factored in with the actual temperature and anything above 41 degree Celsius H1 is considered dangerous to human health. According to the report, ‘Decoding the Urban Heat Stress among Indian cities’, cities are not cooling down at night at the rate they used to during 2001-10. Citing decadal data, the report said the land surface temperature used to come down by 6.2-13.2 degree Celsius from the day-time peak to nighttime peak. In the last 10 summers, the night-time cooling has reduced to 6.2 degree Celsius to 11.5 degree Celsius. Mumbai nights have faced the most reduction in night-time cooling by 24 per cent. Reduction in night-time cooling has far reaching impact on human health. Citing a study published in the Lancet Planetary Health by a group of scientists from China, South Korea, Japan, Germany and the US, the report noted that the risk of death from excessively hot nights could increase nearly six-fold. ALSO READ: Cyclone Remal: 2 killed, nearly 15,000 houses damaged in West Bengal Apart from health, high HI round the clock puts pressure on the power supply load. High use of air conditioners, coolers and refrigerators spikes load even during what used to be low demand hours such as late evening and early morning. High usage of HFC based cooling equipment increases the ambient heat in any area. Cities are becoming hotter with rising use of ACs, several research reports have concluded. Several states have already crossed their record historic high power demand - Delhi (8Gw), Uttar Pradesh (27 Gw), Maharashtra (28 Gw) among others. When it rains, it doesn't pour The CSE report highlighted another worrying trend - Monsoon is more thermally uncomfortable in Delhi, Mumbai, Kolkata and Chennai with their HI being higher than pre-Monsoon period. During 2001-10, the HI used to rise during Monsoon in Delhi, Mumbai and Kolkata while it used to decline in southern megacities of Hyderabad, Bengaluru and Chennai, the report noted. This trend has changed and in the last 10 summers, Monsoon has turned hotter in Delhi, Mumbai and Kolkata, while in Chennai the marginal cooling noted with Monsoon has disappeared, it explained. Anumita Roychowdhury, executive director, research and advocacy at CSE and the research direction for the report, said assessing the changing trend in heat, relative humidity and land surface temperature along with day and night time temperatures is necessary to develop a comprehensive heat management plan for urban centres. “This is needed to implement emergency measures during heatwaves to protect public health and also to develop longer term strategies to mitigate heat by increasing green areas and waterbodies, improving thermal comfort in buildings, and reducing waste heat from vehicles, air conditioners and industries,” she said. Last month, World Meteorological Organisation (WMO) in its state of climate report in Asia said this continent is warming faster than the global average and the warming trend in Asia in 1991–2023 was almost double the warming trend during the 1961–1990 period. On India, it said severe heat waves in April and June resulted in about 110 reported fatalities due to heatstroke in 2023.

How are Delhi residents coping with heatwave?

As Delhi experiences scorching heat, arrangements have been made at several hospitals to treat patients suffering from issues such as exhaustion and stroke. Scorching temperatures in Delhi have forced authorities to issue a red alert for the sweeping heatwave that has disrupted routine activities in the national capital Rohit Garg, a 24-year-old gig worker, was admitted to the capital's Safdarjung hospital when his body temperature rose and he began shivering. Delivering food parcels on his two-wheeler in the blistering heat enveloping Delhi had taken its toll, and he fainted at his last stop. "His sugar level dropped, and he suffered from severe dehydration. We had to put him through rehydration therapy as he suffered a heat stroke," Ashutosh Singh, a doctor, told DW. Jagan Das, a construction worker, has just recovered from a local hospital stay of four days, where he was on intravenous fluid. "I was dehydrated and am fortunate to survive. Working shifts of 10 hours in high temperatures put me down," Das told DW. Sizzling Delhi With Delhi continuing to reel under scorching heat, arrangements are in place at several hospitals to treat patients suffering from heat-related health problems such as exhaustion and stroke. Some have set up dedicated units to treat patients suffering from heat-related health problems. The Delhi government has asked hospitals to initiate a heat-relief action plan and ensure preparedness to deal with Heat-Related Incidents (HRIs). In the last fortnight, 10-15% more heat-related patients have come to OPD and about 10% to the emergency department. "Our hospital staff is being sensitized for quick pick up of diagnosis and we are ready with rehydration therapy, depending on the severity of heat stroke patients," Sumit Ray, medical director of Holy Family Hospital, told DW. With no respite from the heat expected anytime soon, the India Meteorological Department issued a "red alert" about severe conditions in the national capital. Najafgarh in south Delhi recorded a maximum temperature of 47.8 degrees Celsius (118 degrees Fahrenheit), the highest of the season so far. The Delhi government directed the schools that have not closed for summer vacations to do so with immediate effect. Public parks and markets are reporting thin attendance, and zoo authorities have begun to introduce preventive measures such as hosing down animals and installing water coolers in enclosures. Extreme heat affects poor However, no help is forthcoming for Delhi's outdoor workers and low-income households, even though rising temperatures can pose serious health risks. "We bear the brunt of the heatwave — dehydration and heatstroke — almost daily, and there is an absence of basic facilities from the scorching sun," Meena Devi, a daily construction worker, told DW. Many contractors fail to provide essential requirements to their laborers. Lack of access to adequate healthcare facilities and unsafe working conditions pose significant risks to workers' well-being. "It is difficult to work, but if I don't, I won't get an income," said Devi, with her head and face covered by a scarf. She added that the heat also takes a toll on her two young children, whom she brings to the site. Last week, the municipal authorities stopped the water supply, and many people had to make a tortuous walk a kilometer away to fetch water from trolleys filled with buckets. The poor and the homeless, who work or sleep outdoors, have been the worst affected by this climate. Many resort to makeshift measures, such as using tarpaulin and seeking shade near trees and parks, to lessen the impact of extreme heat. "The number of heatwave days has increased. It is not just day temperature that we have to battle, but night temperatures have also been high," Hiralal Paswan, a rag picker, told DW. Coping with extreme heat With temperatures spiking to 50 degrees Celsius, even election candidates and party workers take a break from outdoor campaigning from noon to 3:00 p.m. amid the ongoing election campaign. "When the sun is at its fiercest at this time, our door-to-door campaigning, where workers distribute pamphlets, paste stickers, and tell voters about party symbols, come to a brief halt," Raghu Jain, a political party activist, told DW. "But it is only a temporary reprieve. There is heat stress on the body, and several workers have fallen ill due to sheer exhaustion," added Jain. Measuring the impact of heat can be difficult, and estimates of the number of deaths attributed to scorching temperatures vary from a few hundred to a thousand a year. Dense concentrations of buildings and paved surfaces amplify the temperatures, especially in areas with little tree cover or green space, creating heat islands where poor and minority neighborhoods often bear the brunt. Experts point out that if current warming trends continued, wet bulb temperatures, a measure of heat and humidity indicating the point when the body can no longer cool itself, would be so high that people directly exposed for six hours or more would find it difficult to survive. "A large proportion of our population is highly vulnerable to heatwaves due to the possession of fewer household amenities as well literacy rates literacy and access to water and sanitation," Sunita Narain, director of the Centre for Science and Environment, told DW.

CSE study tracks heat wave; exposes dangerous trends in India’s biggest cities

An unprecedented heat wave has been enveloping Indian cities, worsening the urban heat island effect, this summer. A new analysis by Centre for Science and Environment (CSE) says there are far deeper and longer term evidences on the nature of this changing trend that is impacting India’s biggest cities. The analysis shows that the heat stress is not just about rising temperatures. It is a deadly combination of air temperature, land surface temperature and relative humidity that leads to acute thermal discomfort and heat stress in cities. Even if there is a variation in air temperatures across climatic zones with some parts recording even a decline, the other two factors – relative humidity and land surface temperature — combine to enhance discomfort and heat-related disease burden. According to the US National Weather Service, the heat index is a measure of how hot it really feels when humidity is factored in with the actual temperature. It is considered that a heat index of 41°C is dangerous for human health. “Assessing the changing trend in heat, relative humidity and land surface temperature along with day and night time temperatures is necessary to develop a comprehensive heat management plan for the urban centres. This is needed to implement emergency measures during heatwaves to protect public health, and also to develop longer term strategies to mitigate heat by increasing green areas and waterbodies, improving thermal comfort in buildings, and reducing waste heat from vehicles, air conditioners and industries,” says Anumita Roychowdhury, executive director, research and advocacy at CSE. “Addressing the combination of high heat and humidity is particularly important as this can compromise the human body’s main cooling mechanism: sweating. The evaporation of sweat from skin cools our bodies, but higher humidity levels limit this natural cooling. As a result, people can suffer heat stress and illness, and the consequences can even be fatal even at much lower ambient temperatures. Interestingly, night time temperature is remaining elevated in cities,” says Avikal Somvanshi, senior programme manager, Urban Lab, CSE. Methodology and data: The Urban Lab at CSE has carried out a comprehensive assessment of all three factors during summer – air temperature, land surface temperature and relative humidity – that contribute to heat stress, in six megacities of India. These include Delhi, Mumbai, Kolkata, Hyderabad, Bengaluru and Chennai. The time frame of the study is the summer of January 2001 till April 2024. These six cities are located in different climatic zones and provide insights into regional variations in heat stress. The analysis has focused on the trends in day and night time temperature, humidity levels, seasonal variations, trend in land surface temperature and trend in built-up area. This summary report provides highlights and some key findings from all the cities. The study is based on comparative statistical analysis of temperature and the humidity condition observed in Delhi since 2001. The study’s definition of summer is the period from March to August. It is further divided into pre-monsoon (March-May) and monsoon (June-August) as per IMD classification. This is based on publicly available datasets from various national and global agencies. Ambient temperature and humidity data have been sourced from the India Meteorological Department (IMD) weather stations at Palam and Safdarjung. An average of the findings from these two weather stations is used to represent Delhi in this study. Heat Index computation has been done using the US National Oceanic and Atmospheric Administration’s (NOAA) formula. Complex geospatial calculations have been done in python and ArcGIS. Moreover, freely accessible MODIS Land Science data from NASA Earth Observations has been used for seasonal and long term analysis of land surface temperature. For more granular analysis of heat and land use conditions on extremely hot days, satellite imagery data from the United States Geological Survey (USGS) Earth Explorer website has been used. Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and Landsat 8 operational land imager/thermal infrared sensor (OLI/TIRS) satellite imagery were downloaded and used to analyze the land surface temperature, land use, land cover and Normalized Difference Vegetation Index (Green cover). This city-level assessment focuses on changes in heat patterns over the years for the summer season, urban expansion over the years, and land surface temperature variation during the summer of 2003, 2013, and 2022. Key highlights Decoding decadal trends: Heat trends that add to thermal discomfort and heat stress-related diseases are now being tracked more granularly by technical monitoring bodies. The IMD tracks air temperature at its weather stations: according to its Annual Climate Summary-2023, the year 2023 was the second warmest year on record since nationwide tracking commenced in 1901. The annual mean land surface air temperature averaged over India during 2023 was +0.65°C above the long-term average (period 1981-2010). However, this is lower than the highest warming observed over India during 2016. On the other hand, the recently released World Meteorological Organisation’s (WMO) State of the Climate in Asia 2023 has brought out the variations in land surface temperatures across India. This behaves differently from ambient air temperature trends. This states that the average land surface temperatures were below normal (1991-2020 reference) in parts of the inland Indian peninsula in 2023 even though the mean land surface temperature over Asia was the second highest on record. The WMO’s assessment is based on land surface temperature data derived from satellite observations. The observations of the two agencies show that while air temperatures are higher than average in India, land temperature is below average. Yet, when relative humidity is combined with high heat, it worsens the heat stress and adversely impacts human thermal comfort and health. Overall trends in urban heat stress in mega cities Variations across climatic zones: Cities in the warm-humid and moderate climate zones show an increase, while cities in composite and hot-dry climate zones indicate a decline. Ambient air temperature has changed by less than 0.5°C between 2001-10 and 2014-23. Ambient air in Mumbai, Kolkata, Bengaluru and Chennai has gotten hotter while Delhi and Hyderabad seem to be bucking the trend: Decadal summer-time average ambient temperature has risen by about 0.5°C in Mumbai, Bengaluru and Chennai compared to 2001-10. Kolkata’s decadal average is also up by 0.2°C. Delhi and Hyderabad, two metros which are located in composite climate zones known for the driest and harshest summers, have registered lower decadal average compared to 2001-10. Decadal summer-time average for Delhi is down by 0.6°C and for Hyderabad, by 0.9°C, compared to 2001-10. Relative humidity has increased in all zones: This increase has made heat stress worse in warm-humid and moderate climate zones, while it has nullified the fall in air temperatures in composite and hot-dry climate zones, especially during monsoons. Average relative humidity (RH) has significantly increased in the last 10 summers compared to the 2001-10 average. Barring Bengaluru, decadal summer-time average RH has increased by 5-10 per cent in the other five mega cities. The last 10 summers of Hyderabad have been on an average 10 per cent more humid compared to 2001-10. Similarly, Delhi’s last 10 summers have been 8 per cent more humid. Mumbai’s relative humidity is up by 7 per cent, while summers in Kolkata and Chennai are 5 per cent more humid on an average. Bengaluru has seen no change in humidity levels during summers. Both Delhi and Hyderabad might have registered the biggest rise in RH levels, though they are located in one of the driest climatic zones. This jump in decadal RH still does not bring their overall humidity levels at par with that of other mega cities which are located in more humid climates. Mumbai, Kolkata and Chennai are still over 25 per cent more humid than Delhi and Hyderabad. The increased humidity in Delhi and Hyderabad somewhat nullifies their marginal drop in ambient air temperatures; in the other four cities, it intensifies the heat stress. Heat index rising faster than ambient temperature in all the cities: Given the rise of relative humidity during summers, the heat index (HI) has risen among mega cities. Chennai´s summer average heat index stood at 37.4°C (impact of humidity: 6.9°C) making it the hottest among the mega cities. Kolkata with a summer HI average of 36.5°C (impact of humidity: 6.4°C) and Mumbai with 34.3°C (impact of humidity: 5°C) were almost equally hot. Delhi’s summer HI average stood at 32.2°C (impact of humidity: 3.3°C) and Hyderabad’s at 29.3°C (impact of humidity: 1.2°C). Bengaluru was the least hot among the mega cities with a summer HI average of 26.9°C (impact of humidity: 0.8°C). Monsoons more thermally uncomfortable in Delhi, Mumbai, Kolkata and Chennai with their heat index being higher than during pre-monsoon period. During 2001-10, the HI used to rise between pre-monsoon and monsoon in Delhi, Mumbai and Kolkata, while it used to drop for the southern megacities of Hyderabad, Bengaluru and Chennai. This trend has changed and 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 for Bengaluru and Hyderabad, but the magnitude of cooling has reduced. Overall, monsoons on average have become 1°C hotter while pre-monsoons are hotter by 0.5°C on heat index compared to 2001-10. Cities not cooling down at night at the rate they used to during 2001-10: This phenomena is observed across all climatic zones. During the summers of 2001-10, land surface temperatures used to drop by 6.2°C-13.2°C from the day-time peak. Hyderabad used to cool down at night the most, while Kolkata the least. Now, in the last 10 summers (2014-23), night-time cooling has reduced to 6.2°C-11.5°C. In the current decade, Hyderabad on an average is relatively cooler by just 11.5°C — 13 per cent down from 2001-10 levels. Delhi nights are a little cooler by just 11.2°C: 9 per cent down from 2001-10. Bengaluru nights are cooling down by just 10.1°C (15 per cent down). Chennai nights are cooler by just 9.7°C (5 per cent down from 2001-10), and Mumbai nights by 7.8°C (24 per cent down from 2001-10 level). Kolkata is the only megacity where night-time temperature is cooling down at the same rate as it used to during 2001-10 — but it cools down the least among the megacities with land surface temperature dropping only 6.2°C at night. It must be noted that night-time cooling is getting lesser in the last few years for all megacities compared to the mid-2010s. Says Somvanshi: “Hot nights are as dangerous as mid-day peak temperatures. People get little chance to recover from day-time heat if temperatures remain high overnight. A study published in the Lancet Planetary Health has noted that the risk of death from excessively hot nights would increase nearly six-fold in future. This prediction is much higher than the mortality risk from daily average warming suggested by climate change models.” All cities have registered significant increase in their built-up area that contribute to urban heat island effect: There is direct co-relation between increase in built-up area and increase in urban heat stress. All megacities have become more concretised in the last two decades; this has contributed to the rise in heat stress; increase in green cover can moderate day-time heat, but is not that ineffective in arresting night-time heat. In 2023, Kolkata had the highest percentage of its land under concrete and the lowest green cover among the megacities; Delhi has comparatively the least area under concrete and the maximum green cover. Over the last two decades, built-up area in Chennai has doubled. Kolkata has registered an only 10 percentage points increase in its built-up area, making it the slowest as far as concretization is concerned. Hyderabad has doubled its green cover in the last two decades — fastest among the megacities. Green cover has declined in Mumbai, Kolkata and Chennai. Most decline was noted in Chennai whose green cover shrank by almost 14 percentage points. City-wise highlights Delhi Cooler than previous averages, but high humidity worsening heat stress: March-April of 2024 was 3°C cooler than the average of 2014-23. Delhi’s summer-time has registered a 0.6°C lower decadal average ambient air temperature, but relative humidity has increased by 8 per cent between 2001-10 and 2014-23. High humidity responsible for adding to heat stress: An average 3.3°C of heat stress is being added. City not cooling down at night: Diurnal cooling down of land surface temperature between day- and night-time is down by 9 per cent. Urban heat island phenomena stronger at night: At night, the peri-urban area cools down by 12.2°C, while the city core cools down by only 8.5°C – thus the city core is cooling down 3.8°C less than its peri-urban areas. Direct co-relation between increase in built-up area and rise in urban heat stress: Built-up area has increased from 31.4 per cent in 2003 to 38.2 per cent in 2022. Green cover has increased from 32.6 per cent in 2003 to 44.2 per cent in 2022. Increase in green cover shows impact on daytime temperatures, but it has had no impact on night-time temperatures and the increasing heat index. Monsoons getting more thermally unconformable than pre-monsoons: Average heat index during monsoons is 9.4°C more than pre-monsoons. Mumbai Both air temperature and humidity have increased, worsening the heat stress: Mumbai’s summer-time has registered a 0.6°C increase in decadal average ambient air temperature; relative humidity has gone up by 7 per cent between 2001-10 and 2014-23. High humidity responsible for adding to heat stress: This is adding an average of 5°C of heat stress to the city. The heat index of the city has increased by 7 per cent. March-April 2024 was similar thermally to the average of 2014-23. Both pre-monsoons and monsoons more thermally uncomfortable by over 2°C: Thermal distinction between monsoon and pre-monsoon has disappeared. Not cooling down at night at the same rate as in 2001-10: Diurnal cooling down of land surface temperature between day- and night-time is down by 24 per cent. Urban heat island phenomena stronger at night: During day-time, the core of Mumbai is 3.5°C cooler than its peripheries and peri-urban areas. But at night, the core is 0.4°C warmer. Direct co-relation between increase in built-up area and rise in urban heat stress: Mumbai’s built-up area has increased from 38.4 per cent in 2003 to 52.1 per cent in 2023. Green cover has decreased from 35.8 per cent in 2003 to 30.2 per cent in 2023. Kolkata Normal decadal air temperature change, but higher humidity worsening heat stress: Kolkata’s summer-time has registered insignificant change in decadal average ambient air temperatures, but the relative humidity has increased by 5 per cent between 2001-10 and 2014-23. High humidity responsible for adding an average 6.6°C of heat stress: Decadal heat index has risen by 3.5 per cent on an average. Days with daily heat index exceeding 41°C (danger mark) have tripled compared to 2001-10. Monsoons getting more thermally unconformable than pre-monsoons: Average heat index during monsoons is 3.5°C more than in pre-monsoons. Unlike other metros, Kolkata cools down at night at the same rate as in 2001-10. But diurnal cooling down of land surface temperatures between day- and night-time has a difference of 6°C on an average. During day-time core of Kolkata is 1.8°C warmer than its peripheries and peri-urban areas; at night, the difference is of 1.2°C. This is evidence of urban heat island effect. Direct co-relation between increase in built-up area and rise in urban heat stress: Built-up area has increased from 70 per cent in 2001 to 80.1 per cent in 2023. Green cover has decreased from 15.2 per cent in 2001 to 14.5 per cent in 2023. Hyderabad Air temperature has not seen appreciable increase, but humidity has gone up, worsening the heat stress: Hyderabad’s summers have registered a 0.9°C drop in decadal average ambient air temperatures, but relative humidity has increased by 10 per cent between 2001-10 and 2014-23. High humidity responsible for adding an average 1.5°C of heat stress High number of summer days with high temperatures: Hyderabad has 30-90 days in summer when the daily ambient temperature exceeded the 37°C mark. Pre-monsoons thermally more unconformable than monsoons: Average heat index during monsoon is about 3°C less than pre-monsoon. Not cooling down at night at the same rate as in 2001-10: The diurnal cooling down of land surface temperatures between day- and night-time is down by 13 per cent. Urban heat island phenomena stronger at night: During day-time in summers, the core of the city is 0.7°C cooler than its peripheries and peri-urban areas. At night, the core gets 1.9°C warmer. Direct co-relation between increase in built-up area and rise in urban heat stress: Built-up area has increased from 20.6 per cent in 2003 to 44 per cent in 2023. Green cover has also gone up from 8.9 per cent in 2003 to 26.5 per cent in 2023. This rise in green cover indicates an impact on day-time temperatures, but none on night-time temperatures and the increasing heat index in the city. Bengaluru Rising summer-time temperature, but stable relative humidity: Bengaluru has registered a 0.5°C increase in decadal average ambient air temperature in summers, while relative humidity has remained stable over the last two decades. March-April 2024 was significantly hotter (about 3°C) compared to the average of 2014-23. Humidity responsible for adding an average 0.6°C of heat stress: Heat Index of the city has increased by 2 per cent. Pre-monsoons more thermally unconformable than monsoons: Average heat index during pre-monsoon is 3°C more than during monsoons. City not cooling down at night: Diurnal cooling down of land surface temperature between day- and night-time is down by 15 per cent. Urban heat island phenomena stronger at night: During day-time in summers, core of Bengaluru is 0.6°C cooler than its peripheries and peri-urban areas. But at night, the core is 2.5°C warmer. Direct co-relation between increase in built-up area and rise in urban heat stress: Built-up area has increased from 37.5 per cent in 2003 to 71.5 per cent in 2023. Green cover has also increased from 18.8 per cent in 2003 to 26.4 per cent in 2023. The rise in green cover has had an impact on day-time temperatures, but none on night-time temperatures and increasing heat index in the city. Chennai Both air temperature and relative humidity have increased, worsening the heat stress: A summer-time rise of 0.4°C in decadal average ambient air temperature; relative humidity has increased by 5 per cent between 2001-10 and 2014-23. March-April 2024 was 1°C hotter compared to average of 2014-23. High humidity responsible for adding an average of 6.3°C heat stress: Heat Index of the city has increased by over 5 per cent. More days with high heat index: Days with daily heat Index exceeding 41°C (danger mark) has tripled compared to 2001-10. Both pre-monsoons and monsoons have become thermally more uncomfortable: With about 2°C rise in heat index, thermal distinction between pre-monsoon and monsoon has almost disappeared — both periods are now equally hot and muggy. City not cooling down at night: Diurnal cooling down of land surface temperature between day- and night-time is down by 5 per cent. Urban heat island phenomena is strong: During day-time in summers, core of Chennai is 0.8°C warmer than its peripheries and peri-urban areas. At night, the core is 0.9°C warmer. Direct co-relation between increase in built-up area and rise in urban heat stress: Built-up area has increased from 30.7 per cent in 2003 to 73.5 per cent in 2023. Green cover has decreased from 34 per cent in 2003 to 20.3 per cent in 2023. Trends in heat stress will worsen with climate change: The technical summary of the Intergovernmental Panel on Climate Change (IPCC), Working Group-I, Sixth Assessment Report (AR6 WG-I) notes that the frequency and intensity of heat extremes and duration of heat waves have almost certainly increased since 1950, and will keep rising even if global warming is stabilised at 1.5°C Says Roychowdhury: “Combining climate change projections with urban growth scenarios, it can be said with very high confidence that future urbanisation will amplify the projected increase in local air temperatures.” With reference to urban centres, the IPCC notes with confidence in AR6 WG-II that hot extremes, including heat waves, have intensified in cities. It further notes that urban areas experience air temperatures that are several degrees warmer than surrounding areas, especially during the night. The urban heat island effect can add 2°C to local warming, reducing the adaptive capacity of cities and increasing the aforementioned risks. This is due to reduced ventilation, heat trapping by closely-spaced tall buildings, heat generated directly from human activities, heat-absorbing properties of concrete and urban building materials, and limited vegetation. What should be done? We need heat management plans in our cities Implement city-specific heat management plans: These plans need to go beyond immediate emergency responses to help cope with specific heat events during summer and prevent heat lock-in. Says Somvanshi: “This is not only about summer action for public health protection, but more sustained action throughout the year to heat-proof the city and undertake heat mitigation, along with monitoring, to improve the overall adaptive thermal comfort of built structures and reduce energy and carbon intensity of the built environment.” Target all heat generators: Key heat generators such as concrete built surfaces, barren land and waste heat generators like vehicles, industries, and cooling devices should be brought under the ambit of the plan. Adopt guidelines and action plans to reduce thermal load on buildings and enhance thermal comfort; manage waste heat. Modify land use to mitigate heat: Ensure reversal land-use changes to expand the green areas and waterbodies for stronger cooling effect. Increase shaded areas. Develop a tracking mechanism: This is for tracking annual and diurnal trends in temperature, humidity and overall heat index to inform planning and implementation. Consider both day- and night-time temperatures for planning: Often, health emergency action considers only the high day-time temperatures, and not the night-time temperatures and relative humidity. This trend poses risks to public health and energy security of the city. The heat problem is not just about focusing on daily maximum temperatures crossing the 45°C benchmark — the standard focus during summers — but involves a much more complex set of indices. Strengthen scientific tracking of key factors impacting heat: Develop and combine a robust database on ambient heat and temperature, surface heat absorption and land surface temperatures, and changing land use, including vegetative cover and waterbodies that are determinants of heat island effect and relative humidity. This requires effective leveraging of available satellite technology. Given advancements in technology, such data is available but needs policy integration. Put in place emergency action plans for heat wave episodes to protect public health: It is critical to develop emergency healthcare systems for heat-related disease burden, expand the shaded areas in cities, ensure availability of drinking water in public spaces, and reduce heat exposure for vulnerable and occupationally exposed groups in cities.

Heat wave in India: Why is Delhi unbearable and Bengaluru better? Study explains a worrying phenomena

Delhi, Mumbai, Chennai, Bengaluru, Kolkata, and Hyderabad are facing worsening "heat stress" due to rising relative humidity over the past two decades, says a study by the Centre for Science and Environment (CSE). The study blames it on "urban heat island" effect, where built-up areas trap heat, reduce green cover, cause congestion, absorb heat, and generate additional heat from human activities. This effect makes city centers much warmer, especially at night. High heat and humidity compromise the body's cooling mechanism, making people sick and potentially causing fatalities even at lower temperatures. The combination of rising temperatures and humidity is increasing the heat index, a measure of discomfort. Bengaluru the exception Prolonged heatwaves this summer have intensified the issue, with Odisha recording 18 heatwave days and West Bengal 16 in April. Rajasthan, Haryana, and Delhi are currently experiencing long heatwaves, with no relief expected for at least three more days, according to the India Meteorological Department. The study noted a 5-10% rise in average summer humidity in most metros over the last decade, with Hyderabad seeing the highest increase at 10%. Mumbai, Kolkata, and Chennai saw increases of 8%, 7%, and 5%, respectively. Bengaluru was the exception. Monsoon periods are now hotter in Mumbai and Kolkata, while Chennai has lost its marginal cooling during this season. Bengaluru and Hyderabad remain slightly cooler during monsoon compared to the pre-monsoon period. Why is Delhi looking unbearable The analysis shows that Delhi's extreme heat is directly linked to the increase in built-up areas. As the city has expanded, with built-up areas growing from 31.4% in 2003 to 38.2% in 2022, urban heat stress has intensified. While more green cover helps lower daytime temperatures, it doesn't affect nighttime temperatures or the increasing heat index. This urban expansion traps heat, making the city hotter, especially at night.

India: How are Delhi residents coping with heat wave?

As Delhi experiences scorching heat, arrangements have been made at several hospitals to treat patients suffering from issues such as exhaustion and stroke. DW spoke to some of those affected by the heat wave. Scorching temperatures in Delhi have forced authorities to issue a red alert for the sweeping heatwave that has disrupted routine activities in the national capital. Rohit Garg, a 24-year-old gig worker, was admitted to the capital's Safdarjung hospital when his body temperature rose and he began shivering. Delivering food parcels on his two-wheeler in the blistering heat enveloping Delhi had taken its toll, and he fainted at his last stop. "His sugar level dropped, and he suffered from severe dehydration. We had to put him through rehydration therapy as he suffered a heat stroke," Ashutosh Singh, a doctor, told DW. Jagan Das, a construction worker, has just recovered from a local hospital stay of four days, where he was on intravenous fluid. "I was dehydrated and am fortunate to survive. Working shifts of 10 hours in high temperatures put me down," Das told DW. Sizzling Delhi With Delhi continuing to reel under scorching heat, arrangements are in place at several hospitals to treat patients suffering from heat-related health problems such as exhaustion and stroke. Some have set up dedicated units to treat patients suffering from heat-related health problems. The Delhi government has asked hospitals to initiate a heat-relief action plan and ensure preparedness to deal with Heat-Related Incidents (HRIs). In the last fortnight, 10-15% more heat-related patients have come to OPD and about 10% to the emergency department. "Our hospital staff is being sensitized for quick pick up of diagnosis and we are ready with rehydration therapy, depending on the severity of heat stroke patients," Sumit Ray, medical director of Holy Family Hospital, told DW. With no respite from the heat expected anytime soon, the India Meteorological Department issued a "red alert" about severe conditions in the national capital. Najafgarh in south Delhi recorded a maximum temperature of 47.8 degrees Celsius (118 degrees Fahrenheit), the highest of the season so far. The Delhi government directed the schools that have not closed for summer vacations to do so with immediate effect. Public parks and markets are reporting thin attendance, and zoo authorities have begun to introduce preventive measures such as hosing down animals and installing water coolers in enclosures. Extreme heat affects poor However, no help is forthcoming for Delhi's outdoor workers and low-income households, even though rising temperatures can pose serious health risks. "We bear the brunt of the heat wave — dehydration and heatstroke — almost daily, and there is an absence of basic facilities from the scorching sun," Meena Devi, a daily construction worker, told DW. Many contractors fail to provide essential requirements to their laborers. Lack of access to adequate healthcare facilities and unsafe working conditions pose significant risks to workers' well-being. "It is difficult to work, but if I don't, I won't get an income," said Devi, with her head and face covered by a scarf. She added that the heat also takes a toll on her two young children, whom she brings to the site. Last week, the municipal authorities stopped the water supply, and many people had to make a tortuous walk a kilometer away to fetch water from trolleys filled with buckets. The poor and the homeless, who work or sleep outdoors, have been the worst affected by this climate. Many resort to makeshift measures, such as using tarpaulin and seeking shade near trees and parks, to lessen the impact of extreme heat. "The number of heat wave days has increased. It is not just day temperature that we have to battle, but night temperatures have also been high," Hiralal Paswan, a rag picker, told DW. Coping with extreme heat With temperatures spiking to 50 degrees Celsius, even election candidates and party workers take a break from outdoor campaigning from noon to 3:00 p.m. amid the ongoing election campaign. "When the sun is at its fiercest at this time, our door-to-door campaigning, where workers distribute pamphlets, paste stickers, and tell voters about party symbols, come to a brief halt," Raghu Jain, a political party activist, told DW. "But it is only a temporary reprieve. There is heat stress on the body, and several workers have fallen ill due to sheer exhaustion," added Jain. Measuring the impact of heat can be difficult, and estimates of the number of deaths attributed to scorching temperatures vary from a few hundred to a thousand a year. Dense concentrations of buildings and paved surfaces amplify the temperatures, especially in areas with little tree cover or green space, creating heat islands where poor and minority neighborhoods often bear the brunt. Experts point out that if current warming trends continued, wet bulb temperatures, a measure of heat and humidity indicating the point when the body can no longer cool itself, would be so high that people directly exposed for six hours or more would find it difficult to survive. "A large proportion of our population is highly vulnerable to heat waves due to the possession of fewer household amenities as well literacy rates literacy and access to water and sanitation," Sunita Narain, director of the Centre for Science and Environment, told DW.

Why Are Cities Not Cooling Down At Night? Decoding Heat Stress in Delhi, Mumbai, Bengaluru, Chennai

Why has it been feeling so hot even at night? The phenomenon was studied in India’s bigger cities where it was found that a combination of rising temperatures, humidity and urban expansion is making heatwaves deadlier. According to a study conducted by Delhi-based think tank Centre for Science and Environment (CSE), cities are not cooling down as much as they did during 2001-2010. The study, ‘Decoding the Urban Heat Stress among Indian Cities, analysed data from six major cities – Delhi, Mumbai, Kolkata, Hyderabad, Chennai and Bengaluru – over a period of 23 years (January 2001 to April 2024). The study highlighted while some cities have not seen a significant rise in temperatures but the humidity levels have left people stressed. Heat stress results from a combination of air temperature, land surface temperature, and relative humidity, causing “acute thermal discomfort and increased heat-related diseases in cities”, as mentioned in a report by Down to Earth. Even if air temperatures vary, high relative humidity and land surface temperatures exacerbate discomfort. According to the US National Weather Service, the heat index is a measure of how hot it really feels when humidity is factored in with the actual temperature. It is considered that a heat index of 41°C is dangerous to human health. HOW HOT HAS DELHI BECOME According to the CSE analysis, Delhi’s ambient air temperature “shows little change” over the past 10 summers compared to the 2001-2010 decade. However, the “nature of heat is changing” with a significant increase in relative humidity over the past 10 summers. The last 10 summers (2014-23) in Delhi have been 8% more humid on average compared to the average relative humidity from 2001-2010. While the average relative humidity for the summers from 2001 to 2010 was 52.5%, in the summer of 2023, this was as high as 60.9%. Similarly, in 2020, it was 61.4%, while it was 57.3% in 2021, and 53.5% in 2022, going by the analysis.

Bengaluru hotter by 3°C compared to 2014-23

BENGALURU: The recent heat wave conditions experienced in Karnataka is being experienced by most Indian cities, and the condition is only worsening because of the increasing heat island effect, noted Centre for Science and Environment (CSE) in its report released on Monday. The CSE tracked the heatwave conditions of the six metro cities in India - Bengaluru, Chennai, Kolkata, Mumbai, Delhi and Hyderabad, for their study, and analysed that the nature of this changing trend impacting India cities goes far deeper and longer. The analysis also showed that the heat stress was not just about rising temperatures. It is a combination of air temperature, land surface temperature and relative humidity that lead to acute thermal discomfort and heat stress in the cities. In its report, CSE noted that increasing relative humidity had worsened the heat index (which is a combination of air temperature and relative humidity) and heat stress in daily lives. It also noted that cities were no longer cooler at night, and highlighted that all these cities had registered a significant rise in their built up areas and concretisation, which contributed to the urban heat island effect. There was an urgent need for a heat management action plan to expand green areas and water bodies, reduce thermal load on buildings and improve thermal comfort and implement emergency measures during heat wave episodes to protect public health, noted the report. Bengaluru had registered a 0.5°Celsius increase in decadal average of the ambient air temperature in summers, while relative humidity remained stable over the last two decades. March - April 2024 was significantly hotter (by about 3°Celsius). The report also noted that humidity added 0.6°Celsius of heat stress on average, and the Heat Index of the city increased by 2%. The pre-monsoon period was thermally more unconformable than monsoon, as the average heat index had increased by 3°Celsius. Avikal Somvanshi, senior programme manager, Urban Lab, said, hotter nights are as dangerous as mid-day peak temperatures, as people get little chance to recover from the day-time heat.

Rising ‘heat stress’ in six metros as humidity up, nights warmer: Study

The combination of rising air and land surface temperatures and high relative humidity is increasing the heat index and heat stress in these cities, the study said. Heat index is a measure of discomfort felt due to high heat and humidity. India’s megacities of Delhi, Mumbai, Chennai, Bengaluru, Kolkata and Hyderabad are experiencing worsening “heat stress” due to a trend of rising relative humidity over the past two decades, according to a study by Delhi-based Centre for Science and Environment. Besides rising relative humidity, these cities are also experiencing warmer nights as land surface temperatures are not falling at the same rate as a decade ago, said the analysis, blaming this on the “urban heat island” effect.

Delhi: Why Narela, Mungeshpur are boiling hot

NEW DELHI: About 50 km north of the city centre, there is a school set amid some trees and open agriculture fields. For the past few weeks, Jawahar Navodaya Vidyalaya has been somnolent. The school is closed for summer and only a few staff planning the coming academic session come for a few hours. It is just as well. The temperature logged at the school was a fiery 48.8 degrees Celsius on Monday, hotter than 48.3 degrees on Sunday. Jawahar Navodaya Vidyalaya in northwest Delhi’s Mungeshpur village doubles up as an automatic weather station (AWS). It has been recording the city’s hottest maximum temperature for the past few days. “It’s excessively hot, almost as if it is raining fire,” exclaimed Pradeep Kumar, the school vice-principal. “Last year, at peak summer, there were no heatwaves. It even rained occasionally. Even a year before that, the summer hadn’t been as punishing.” Why Narela, Mungeshpur Are Boiling Hot Kumar’s colleague Sarveshwar took TOI towards a small tower in the school garden. It was bounded with an enclosure and surrounded by large trees. A board read, ‘India Meteorological Department. Pointing at the tower, Sarveshwar said, “This is where the city is recording its highest temperature as printed in the newspapers.” Not far from there is Narela, which too is among the hottest spots in the city. The daytime temperature on Monday was a sizzling 48.4 degrees Celsius. This mercury mark was recorded at another tower, this time located deep in the lush green planation of the Indian Air Force base station. Both the AWS at Narela or Mungeshpur are at a distance from concrete structures, the industrial belt, tarred roads, etc. And yet they continue to record the highest maximum temperatures in the city, with the readings rising further upon moving away from the AWS towards the markets, industrial areas and the vehicle-filled roads. At the base weather station at Safdarjung, the thermometers have been touching the 45 degrees Celsius mark. But some outer regions, such as Mungeshpur, Narela and Najafgarh, have been grappling with more severe heatwaves, with the mercury breaching the 48 degrees point. “Air conditioners fail to cool the room, the nights are hot and deprives us of proper sleep,” grumbled Sanjay Sherawat, 62, in Auchandi, a village near Mungeshpur. “Almost everyone here complains about painful eyes. I do not remember this village being as sweltering earlier.” According to weather experts, certain parts of Delhi are vulnerable to the early arrival of hot winds from Rajasthan that exacerbate the oven-like weather conditions. These areas are the first to bear the brunt of the hot winds. “Areas like Mungeshpur, Narela and Najafgarh are in the frontline and take the first blow of the hot summer westerly or north-westerly blowing in from Rajasthan or Haryana. This is one of the major reasons why it’s so hot there,” explained Kuldeep Srivastava, senior weather scientist, IMD. However, there are several other factors such as large open areas, barren land and industrial activities that add to the boiling effect. “Look at the larger land use at these locations. Sometimes, despite plantations, there are patches of barren land, say open ploughed fields, that result in an increase in the land surface temperature,” pointed out Anumita Roychowdhury, executive director, Centre for Science and Earth. “There are many waterbodies around. In industrial areas, there is heat emission which feels just like if one were standing behind an air conditioner. Concrete, of course, also radiates heat.” All these add to the simmering heat, making these spots veritable hells in the capital.