This is a CATCH story<\/strong><\/p> This story is part of Dialogue Earth\u2019s work on the Community Adaptations to City Heat (CATCH) project, in partnership with Boston University. The project is funded by Wellcome. All Dialogue Earth content is editorially independent.<\/p><\/div><\/div>\n\n\n\n Last year, Boston declared two heat emergencies, meaning temperatures reached levels that are deemed a threat to health. But because of the complex nature of urban heat, some neighbourhoods are experiencing even more heat than is captured by those warnings.<\/p>\n\n\n\n Patricia Fabian, who works on heat and health at Boston University, has found that a distance of just a few blocks can make a huge difference to temperature. In one week in June 2021, her team measured average temperatures in Chelsea and East Boston that were 3.3C (6F) higher than reported by the National Weather Station for Boston. That station is located at Logan Airport \u2013 a short distance as the crow flies but a world away in heat terms. The team measured peak temperatures over 5.6C (10F) higher than the weather station.<\/p>\n\n\n\n \u201cThere were neighbourhoods [that met] heat advisory or emergency thresholds for 10 days in the summer, but the city only declared four heat advisory or emergency days,\u201d says Fabian. \u201cBecause the heat thresholds are based on temperatures that are predicted from the National Weather Station data, which is measured at the airport.\u201d<\/p>\n\n\n\n Globally, heat stress is the leading cause<\/a> of weather-related deaths. When it comes to heat and health, a few degrees can make a big difference.<\/p>\n\n\n\n Extreme heat can kill the most exposed and the most vulnerable and is linked to a range of long-term health problems, such as kidney disease and mental health problems. It is also leading to the spread of vector-borne diseases.<\/p>\n\n\n\n Those living in cities are particularly at risk. This is partly because cities are often warmer than surrounding countryside due to the urban heat island effect. It is also because they often house particularly vulnerable people, such as the elderly, poor and otherwise disadvantaged groups.<\/p>\n\n\n\n Cities are often warmer than the countryside that surrounds them. This is due to a combination of factors: there are typically fewer trees to provide shade and cooling; a greater number of concrete and brick buildings, which can absorb heat; and more energy use, which produces waste heat. The result is known as the urban heat island effect.<\/p>\n<\/div><\/div><\/div>\n\n\n\n Jessica Lee, the National Weather Service public programme coordinator, says the service \u201crecognises that observing stations cannot always perfectly represent the diverse microclimates of surrounding areas\u201d.<\/p>\n\n\n\n The service pulls other data and information together with sensors to try and build a \u201cmore complete\u201d picture of weather and its impacts, Lee says. It uses forecasts to try and predict heat events and issue warnings, and works with local community groups and public health officials \u201cto determine appropriate heat-alert criteria for specific areas\u201d.<\/p>\n\n\n\n Boston is not the only US city trying to get to grips with this issue. Researchers working in the urban area around Miami found<\/a> their hyperlocal observations had maximum temperatures 3.3C higher than at the National Weather Service site, as well as maximum \u201cheat index\u201d values that were 6.1C higher. That site is located at the region\u2019s international airport, like Boston\u2019s.<\/p>\n\n\n\n The heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature. Source: NWS<\/a><\/p>\n<\/div><\/div><\/div>\n\n\n\n The same thing has been found in New Orleans via work from ISeeChange<\/a>, a community-driven platform for sharing weather observations. And cities outside the US are experiencing something similar.<\/p>\n\n\n\n In Delhi, one of the world\u2019s most polluted<\/a> cities, summers have grown noticeably hotter and more humid in recent years. Both day and night-time temperatures have been rising, and relative humidity levels have increased by up to 9%<\/a> since 2011.<\/p>\n\n\n\n Between March and June 2024, there were 733 deaths due to heatstroke in 17 states in India, with 193 in Delhi alone, notes<\/a> a study by non-profit HeatWatch.<\/p>\n\n\n\n But the city does not heat evenly. Official temperature readings come from a weather station in the Safdarjung area. Yet other areas like Narela, Najafgarh, and parts of Northeast Delhi often record higher local temperatures<\/a>. These neighbourhoods, characterised by industrial activity, less tree cover, more concrete surfaces and limited access to electric fans and air conditioning, have become urban heat hotspots.<\/p>\n\n\n\n \u201cThere are big differences in the structures of houses in elite neighbourhoods and informal settlements. The former has electricity and passive ventilation, so there is less heat trapping. The other has tin roofs, cement block walls, and a steel door,\u201d says Aditya Valiathan Pillai, a visiting fellow at the Sustainable Futures Collaborative and a researcher focused on heat governance.<\/p>\n\n\n\n \u201cTo understand hyperlocal heat mapping, spatial inequalities have to be taken into account.\u201d<\/p>\n\n\n\n India\u2019s response to heat has been heat action plans, implemented by the India Meteorological Department and the National Disaster Management Authority. These are meant to guide cities in preparing for heatwaves.<\/p>\n\n\n\n India\u2019s first such plan was launched in Ahmedabad in 2013 and was soon credited<\/a> with reducing heat-related deaths. But despite the initial success, experts point out<\/a> that most of the plans lack heat index-type information on how hot it actually feels for people, locally defined heat thresholds, and are not localised enough.<\/p>\n\n\n\n The India Meteorological Department\u2019s current heat alerts, which were created as part of the heat action plans, are citywide and based on thresholds that do not capture microclimates. Delhi launched its own heat action plan in 2023 but it has little to say about ward-level planning and does not have a localised heat-mapping system.<\/p>\n\n\n\n As extreme heat has such uneven impacts, some experts are now calling for the use of granular and local insights on the interplay of rising heat hazards, exposure levels and the inherent vulnerabilities of different populations. <\/p>\n\n\n\n Experts in both Boston and Delhi say heat warnings need to be issued with an understanding of more than just temperature.<\/p>\n\n\n\n Heat exposure and vulnerability can vary drastically within just a few kilometres in Delhi. One major blind spot is the migrant labour population, many of whom work and live in the hottest parts of the city.<\/p>\n\n\n\n \u201cThe problem with heat warnings today is that not everyone who needs it gets them,\u201d says Pillai. \u201cHow do we make the information available to those who are most exposed?\u201d<\/p>\n\n\n\n Granular planning can make a real difference, Pillai says. For example, in some densely populated low-income areas, a public loudspeaker may be more effective than an SMS alert. Yet most current heat action plans overlook such community-level specifics.<\/p>\n\n\n\n \u201cI don\u2019t think the bureaucracy understands at the hyperlocal level what heat is, which is why you get all these coordination problems,\u201d he says.<\/p>\n\n\n\n Crucially, people also need the ability to act on warnings. Many of Delhi\u2019s migrant labourers have no enforceable protections, such as limits on maximum working temperatures. Existing government advisories recommend<\/a> measures like rest breaks, water and shade, but these are not enforceable rights.<\/p>\n\n\n\n \u201cAre there social protections that allow people to actually respond to this information?\u201d Pillai asks. \u201cJust giving them heat information when the structure doesn\u2019t allow you to do anything is completely pointless.\u201d<\/p>\n\n\n\n In the US, <\/em>Lee from the National Weather Service says work is underway to get more localised. \u201cThe NWS is investigating technological solutions for more localised alerts, including heat warnings. This would allow forecasters to more precisely target regions with high confidence for extreme heat, moving beyond current geopolitical boundaries like zones or counties,\u201d she says.<\/p>\n\n\n\n She notes that increased precision in warnings will require both more observations of heat, and communicating why some areas are receiving warnings and others are not. \u201cAgency-wide efforts are underway to further localise alerts, not just for heat warnings,\u201d she says, adding that this includes \u201can ongoing urban heat mapping effort to help understand which areas are more susceptible to extreme heat\u201d.<\/p>\n\n\n\nDegrees of difference<\/h2>\n\n\n\n
Delhi is thinking local too<\/h2>\n\n\n\n
How best to warn the most vulnerable?<\/h2>\n\n\n\n
From the top to the bottom<\/h2>\n\n\n\n
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