In July and August 2003, a heatwave unprecedented since at least 1540 struck northern Europe. Temperatures soared well above , the threshold required in most regions for a heatwave to be declared officially by the Met Office. Around 15000 deaths in France, 3100 in Italy, 2100 in Portugal, 2000 in the UK and hundreds elsewhere have been attributed to the event, mostly in the over-75 age-group. But the effects were felt across the wider population, through increased discomfort, diminished water supplies, railway disruption due to track buckling and the deaths of livestock in the fields. Under current projections the problem is set to get worse as a result of climate change, which most scientists expect will make heatwaves more common and more extreme in the coming decades. But according to some researchers, the effects of these heatwaves could be even worse than might be expected from such forecasts.
The reason is that most people do not live in the green, rolling countryside for which forecasts are made. Most people live in cities, and the urban environment, it has slowly dawned on us, behave quite differently to their rural surroundings. Cities trap heat, in a phenomenon that has come to be known as the ‘Urban Heat Island’ effect, and are likely to get even hotter for longer periods than was formerly assumed. If we are to avoid even worse consequences than those witnessed in 2003, our cities are going to have to adapt to reduce this effect, and to do so soon. The heat island effect is very much dependent on the size and topography of a city, and small, green-hearted Durham is unlikely to see temperatures elevated far beyond the surrounding fields. The main concern with future heatwaves in the UK therefore lies in the large metropolises, and the good news is that many of these are already taking steps to ensure that the next time we have a repeat or elevation of the 2003 situation we’re better prepared to avoid lethal consequences.
The first thing we can do is to map the variation in temperature across each city. Tucked away in the centre of Birmingham, unheeded by the scores of motorists zooming through the heart of ‘car city’, sits a weather station that is helping us to do just that. By comparing this station’s measurements to those taken in the standard Met Office weather stations on the outskirts of Birmingham, researchers have identified a heat island effect of as much as during warm weather. By adding to this crude comparison a network of smaller, temporary sensors dotted across the conurbation, we are slowly building up a detailed picture of the parts of the city where temperatures are highest, and the results are not surprising. The city centre, shaded from cool winds blowing in from the countryside or the coast by buildings and warmed by the heat output of myriad people, vehicles and buildings, which themselves are made of materials that tend to strongly absorb and re-radiate heat, turns out to be by far the warmest place, a result that we can expect would be repeated across all metropolises.
What makes this result particularly troubling is that the more built-up parts of the city, where the temperatures are higher, are likely to be the living and working spaces of much more of the population than the greener areas where parks and other green spaces predominate. To assess the potential risk from a heatwave for each region of Birmingham, researchers had to use population statistics to establish where people particularly susceptible to heat tend to live. The heat island is most dangerous where vulnerable populations coincide with high temperature elevations, and this is exactly where city planners have to look when it comes to minimising the health risks that might ensue if nothing was done before the next big heating event.
Vulnerability to heat is increased by a number of factors. Elderly people, as a result of their general frailty and the increased prevalence of various diseases amongst their population, are particularly vulnerable, as are those suffering from respiratory and cardiovascular diseases and conditions such as asthma, since these are likely to be directly aggravated by the warmth. But other, perhaps less obvious conditions, are of equal concern. Those suffering from physical or mental disabilities or depression are all at risk because they may be unable or disinclined to drink more water as the temperature rises, whilst people with diabetes or who are taking thirst-suppressing drugs could also more easily slip into dehydration. Quality of accommodation itself can be an additional risk factor: those living towards the top of high-rise buildings or in areas of high population density will experience greater heat than those elsewhere within any given region of a city.
Some of these risk-factors can be mapped, and individuals warned to move to cooler areas or take extra steps to cool down their local environment in order to combat the extensive health risks. These risks, researchers are discovering, are extensive. Whilst a heatwave is unlikely to raise temperatures in the UK as high as internal body temperature, blood vessels can begin to dilate and direct blood away from essential organs, simultaneously putting excess strain on the heart, as soon as the external temperature exceeds normal skin temperature, which is around . For every degree the temperature rises above this, the body finds it harder and harder to adapt, and heatstroke or dehydration, both of which are potentially fatal, become increasingly likely. At the same time, air pollutant levels appear to be increased by the heat, which only compounds the problem. Climate change, because it aggravates and encourages dangerous heatwaves, won’t simply bring about more clement summer-holiday weather and a few alterations to the types and quantities of crops that can be grown in the UK. It will have, it’s becoming clear, a potentially lethal impact on our population centres.
Even as studies into city temperature and population profiles progress, attention is beginning to shift onto what cities can do to alleviate this catastrophe waiting to happen. Because green areas have been shown to be considerably cooler than built-up ones, and bring about greater aesthetic value and air quality for the local population, we might expect inner-city trees to be the first port of call for planners seeking to transform our city-scapes for a healthier world. But trees, and their associated leaves, can get in the way of urban life, and so new ideas such as green roofs on buildings designed to cool their interiors are being trialled. The next time you exit Birmingham New Street station, have a look for the ‘green wall’ designed to easily bring foliage into the heart of the city. Such schemes have the additional benefit of providing wildlife corridors, helping to support natural ecosystems in an otherwise sterile environment, and should absorb some of the particulates emitted by cars, busses and trains. Whether or not these schemes are shown to be effective, it is likely that we shall see our cities transformed over the coming years, into much greener, healthier and ultimately perhaps more pleasant places to live.