Why Heat Warnings Need To Get More Local

The US city of Boston is more often associated with freezing winters than heatwaves. But as the world warms due to climate change, it is facing up to a hotter future.

In the last three decades of the 20th century, there were an average of 11 days a year on which temperatures in Boston exceeded 32C (90F). It has been estimated that by 2030 there will be 40. And by 2070 there could be 90.

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.

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 – 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.

“There 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,” says Fabian. “Because the heat thresholds are based on temperatures that are predicted from the National Weather Station data, which is measured at the airport.”

Degrees of difference

Globally, heat stress is the leading cause of weather-related deaths. When it comes to heat and health, a few degrees can make a big difference.

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.

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.

Jessica Lee, the National Weather Service public programme coordinator, says the service “recognises that observing stations cannot always perfectly represent the diverse microclimates of surrounding areas”.

The service pulls other data and information together with sensors to try and build a “more complete” 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 “to determine appropriate heat-alert criteria for specific areas”.

Boston is not the only US city trying to get to grips with this issue. Researchers working in the urban area around Miami found their hyperlocal observations had maximum temperatures 3.3C higher than at the National Weather Service site, as well as maximum “heat index” values that were 6.1C higher. That site is located at the region’s international airport, like Boston’s.

The same thing has been found in New Orleans via work from ISeeChange, a community-driven platform for sharing weather observations. And cities outside the US are experiencing something similar.

Delhi is thinking local too

In Delhi, one of the world’s most polluted 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% since 2011.

Between March and June 2024, there were 733 deaths due to heatstroke in 17 states in India, with 193 in Delhi alone, notes a study by non-profit HeatWatch.

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. 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.

“There 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,” says Aditya Valiathan Pillai, a visiting fellow at the Sustainable Futures Collaborative and a researcher focused on heat governance.

“To understand hyperlocal heat mapping, spatial inequalities have to be taken into account.”

India’s 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.

India’s first such plan was launched in Ahmedabad in 2013 and was soon credited with reducing heat-related deaths. But despite the initial success, experts point out 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.

The India Meteorological Department’s 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.

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.

How best to warn the most vulnerable?

Experts in both Boston and Delhi say heat warnings need to be issued with an understanding of more than just temperature.

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.

“The problem with heat warnings today is that not everyone who needs it gets them,” says Pillai. “How do we make the information available to those who are most exposed?”

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.

“I don’t think the bureaucracy understands at the hyperlocal level what heat is, which is why you get all these coordination problems,” he says.

Crucially, people also need the ability to act on warnings. Many of Delhi’s migrant labourers have no enforceable protections, such as limits on maximum working temperatures. Existing government advisories recommend measures like rest breaks, water and shade, but these are not enforceable rights.

“Are there social protections that allow people to actually respond to this information?” Pillai asks. “Just giving them heat information when the structure doesn’t allow you to do anything is completely pointless.”

From the top to the bottom

In the US, Lee from the National Weather Service says work is underway to get more localised. “The 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,” she says.

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. “Agency-wide efforts are underway to further localise alerts, not just for heat warnings,” she says, adding that this includes “an ongoing urban heat mapping effort to help understand which areas are more susceptible to extreme heat”.

The NWS also has a tool called HeatRisk that uses temperature forecasts, climate information and health data to translate the potential impact of heat into a colour-coded scale of five levels, from green (“Little to no risk from expected heat”) all the way to magenta (“Extreme: Rare and/or long-duration extreme heat”). It offers localised heat risk information for the whole of the US.

Julia Kumari Drapkin is CEO and founder of ISeeChange, which undertook the New Orleans monitoring. She says heat warnings need to be looked at both in a top-down way and from the bottom up.

ISeeChange’s AI-powered platform aggregates observations shared by local residents, local sensor networks and historical data. It works with cities, utilities and engineers to help them respond more efficiently to extreme weather impacts like flooding and extreme heat. Cities that have deployed the platform include Miami and New York, as well as New Orleans.

“Maybe people will snap a picture of where they’re experiencing a heat or flood risk or an issue, and then we deliver that data straight to the people who might need it,” explains Drapkin. “That could be a public works department, that could be a health department, that could be an emergency responder, that could be a resilience planner.”

Those using the system can also request information from residents about how they are experiencing heatwaves or other events, adding data to the picture.

Drapkin points out that ISeeChange is the flood reporting tool for the City of Miami, other parts of South Florida, and the Sewerage and Water Board of New Orleans. Building systems like this requires those with power and money to engage with the problem of heat.

“But heat has not really been owned as a problem by any one department at a city, county or even at the federal level,” she explains. “Even chief heat officers are not given departmental budgeting authority, so what we find is that having an organised conversation around heat risk is quite challenging from a lack of ownership and governance, not technology.”

Keeping pace with a changing climate

As Delhi and other Indian cities struggle to protect residents from deadly heat, their action plans need to go beyond being just reactive.

“The heat action plans are responding to something that happened last year. There’s already more carbon in the atmosphere than last year,” says Pillai of the Sustainable Futures Collaborative. “Climate change has not been factored in at all in the responses.”

Globally, the issue of hyperlocal heat warnings will only become more important as cities grow ever larger and the world warms.

“Most people live in cities,” says Fabian of Boston University. “We know that there’s an urban heat island effect; we now know that there’s local urban heat island effects. Cities have to take that information and say: ‘Okay, we know there’s differences in our city. How do we deploy resources differentially?’

“There’s a gap in keeping residents safe with the right information.”

Until heat strategies become anticipatory and inclusive, the risk is that the most vulnerable will remain unprotected, in Boston, New Orleans, Delhi and elsewhere.

(Published under Creative Commons from Dialogue Earth)