Early warning system for heat waves: How an Austrian research project detects hotspots – and makes protective measures more targeted

Prof. Klimek from the Complexity Science Hub Vienna (CSH) explains: “The aim is to better understand how heat affects different areas of care. How great is the respective risk depending on the health situation and what countermeasures make sense? We want to understand heat risks so well that we can predict where more health problems are likely to occur. In the final phase of the project, we will break the results down to the microclimate and building planning level.” This data will also be used for site planning in the future.

The information is crucial for elderly people, nursing homes, mobile services or rescue organizations: Who needs to be especially careful, and when? Where are additional resources needed early on—for example, in which hospitals and departments do we need to allocate more staff? This is crucial for emergency organizations because they cannot spontaneously increase their capacities. This is precisely why advance warning times are needed that are not just general (“it’s getting hot”), but are really suitable for detailed planning.

The project has three main objectives:

1. Measure and understand how heat is linked to hospitalizations, rescues and deaths.
2. Assessing what heat waves mean for an ageing population.
3. Translating this into practice, i.e. better information for those affected and concrete packages of measures for facilities – from care homes to emergency services.

Not more alarm – but more guidance on specific heat consequences

The challenge: There have long been many tools and warning systems, and with the weather apps on our smartphones, practically all of us have heat alarms. However, a hot day in the weather app often says little about how severe the strain actually is. Heat builds up on a densely built-up street; apartments heat up, and the night brings little relief. Just a few kilometers further on—with more greenery, more wind, and different architecture—conditions can be significantly more bearable. Until now, there has been a lack of information on when and where heat becomes truly critical in specific service areas. Another goal was to determine at what temperature and over what duration heat becomes dangerous.

The analyses show that employees in the care and medical sector generally feel well provided with general information – for example, about the effects of heat on the body, health and psyche. What is rather lacking is knowledge about how heat can affect medication. Do they work better or worse when it is very hot? It is also relevant for first aid if medication is stored in the emergency vehicle – and the vehicle is parked in the sun. Prof. Klimek: “Many specific influences are not immediately apparent. The aim is to process these effects more precisely.”

For the hospital sector, data from 2007 to 2019 was used to evaluate whether hospital admissions or deaths occur more frequently during heatwaves than in comparable summer phases without heatwaves. The number of hospital admissions does not increase dramatically overall, according to Prof. Klimek, because inpatient admissions are often planned for operations, for example. But the situation becomes more critical when heat persists over a longer period of time: “We see a very strong signal in hospital mortality, depending on the intensity and duration of the heatwave. If the maximum daily temperature was above 30 °C on five days in the previous two weeks, the risk increases by around 5 to 10 %. If such a phase lasts for two weeks, the risk increase can be up to 20 %.”

Heat is not the same everywhere – and not equally dangerous for everyone

The picture is heterogeneous depending on the diagnosis: Across all age groups, mortality is increasing for several disease groups. Older and very old people are particularly affected, but there is also an increased risk among younger people – albeit at a much lower level.

Not only cardiovascular and respiratory diseases are affected, but also metabolic diseases, psychological and mental illnesses – such as dementia – can have significant effects in some cases. Prof. Klimek: “We are talking about several hundred deaths across Austria that could occur over the course of a summer. We are currently looking at climate model calculations to see how much the number of cases will increase in the coming years as a result of climate change.”

At the same time, it is clear that a large part of the burden is particularly visible in the acute care system: In rescue operations, in acute care – in situations where people suddenly can no longer cope. Prof. Klimek: “We took a particular look at the situation in Vienna. The more intense a heatwave is, the greater the increase in the number of emergency and ambulance calls – by up to 10% on extremely hot days. If you look at the causes, heatstroke is obviously at the top of the list. However, respiratory diseases such as COPD and asthma also play a major role, followed by cardiovascular diseases.” Accidents and attacks are also on the rise: This suggests that we become more clumsy in the wake of heatwaves, and aggression is also on the rise. Women are more affected by these developments than men.

The challenge now is to determine the optimal timing for issuing a warning ahead of an approaching heat wave, tailored to the specific healthcare settings of at-risk groups: in other words, when a warning makes sense. This, in turn, depends on the processes and procedures within care organizations and healthcare facilities. “A Google Alert on a cell phone is far too vague for this,” explains the researcher. “Timely, specific warnings are a key factor in operational planning. Because even if there are only 2 or 4% more cases, that translates, for example, into more emergency vehicles that need to be on standby. And the staff behind them must also be ready.” For institutions, the focus is not on developing high-tech measures to improve heat resilience, but on establishing simple, easy-to-implement routines in a timely manner: drinking more fluids, keeping rooms dark, ventilating properly, and raising awareness.

The first heatwave is often the most dangerous

Particularly important for adaptation measures: “We see a much stronger effect in the first major heatwave of a year than in subsequent ones,” says Klimek. Many people are taken by surprise, they are not yet in “heat mode” and routines such as drinking more are not yet adapted. Prof. Klimek was particularly surprised that heat has such an intense after-effect: “There are strong, measurable delayed effects.” After a heatwave, the stress can persist for several days: “Even if the heatwave has already been over for three days, we still find an effect that is just as strong as if the heatwave were still going on.” The reason for this is often the building stock: Buildings store heat and the apartments only cool down slowly.

Prof. Klimek concludes: “Compared to projects in southern European countries such as Spain or Greece, we are still operating on a different scale. But as soon as the duration and intensity of heat come together, the risk increases significantly here too – then heat will also become a relevant issue in Austria. And these risk windows will increase. Our project should help to intervene in a targeted manner and prevent the consequences of heat as far as possible. Because even if it does not yet reach the same proportions as in other countries, we will also have to adapt in Austria.”