Urban heat islands, a growing problem

Urban heating, or at least the increase thereof, has been in the spotlight for some time. And the basic effects were known to me. But after hearing a lecture by Math Santamouris during a recent Conference, a whole new world opened up for me. He gave a good overview of the state of affairs and developments in that area, and there is much more than I suspected. It is one of those developments that counteracts global warming, as long as we do not intervene drastically. (gentle surgeons and such) A short report.

It is of course known that a stony environment is the major source of heat collection under the sun. It retains a lot of solar heat, which can go up to 5 degrees or more compared to non paved areas. In a city in Morocco, even a 7-degree difference between the old town with narrow streets and the spacious ‘new’ French suburbs is no exception. In the past, those narrow streets were designed precisely for that. And that is still apart from the difference between city and countryside.

Such a temperature difference is of course an advantage in a country with cold periods, the number of heating degree days is substantially less in an urban environment than outside, further enhanced by less wind cooling. However, that does not outweigh the increasing cooling load in the summer, at least for cities that also have sunny and warm summers . And there are more and more of these cities, with climate warming and an increasing number of heat waves. ( as we have in the Netherlands nowadays, sometimes up to 40 degrees) A meta study shows that the heat island effect leads to an average of around 23% more cooling demand, compared to a 19 pct reduction in heating demand, resulting in a total increase of 11% in energy consumption.

That puts an increasing burden on energy networks, which in some parts of the world already can’t cope with that. In rich countries, which are in a transition to sustainable energy, this is certainly leading to an increasing need for solar and wind farms to generate the energy for that cooling, certainly with the continuing warming of the climate. If only the construction of for instance wind farms could keep up with that. After all, one of the biggest energy consumers today, and especially of cooling energy, are data centers: the demand seems to be growing faster than we can construct offshore wind turbines (and the ING bank recently predicted that datacenters in 2030 would consume up to 31 pct of the electricity demand).

It is therefore a self-reinforcing phenomenon: more cooling means more energy consumption, more CO2 emissions, at least for the time being. Apart from other environmental effects, higher temperatures even cause fluctuations in the ozone low concentration, due to accelerated chemical reactions in the atmosphere, with consequences for the local cooling demand. Research shows that with the current trend, a city like Mumbai will have a higher energy demand in 2050 than the entire US combined. With all its consequences. The cooling load can even increase to 100% in some cities, as well as the peak electricity demand.

Measures must mainly be sought in passive and preventive interventions, because more technology and energy will have the opposite effect. Urban heating is then a self-reinforcing phenomenon.

Apart from the energy effects, there are also many costs and / or health effects, and especially in densely populated, poorer city regions. Indoor temperatures can therefore run high, combined with poor indoor air quality , since windows and doors are kept closed in non-ventilated rooms. With CO2 concentrations that can go far above 1500 ppm. Above 800 ppm you can clearly see effects on the cognitive system, for example loss of concentration. At 1000 ppm about 10%, rising to 40% loss of the cognitive function at 1500 ppm.

The mortality chances are also increasing: research shows that the mortality in the same city can be up to 6% higher for those who live in the warmer districts than residents of the cooler districts. Of course, due to the average increase in the Urban Heat island effect, the risk of death for both increases to about 4% at present, with an outlier in parts of Sao Paolo with a 30% higher risk of death.

However, it is not only doom and gloom. Surprising is the research that shows that the human body also adapts to higher temperatures. A few studies showed that the mortality probability can decrease slightly over a longer period. Surprisingly, although we have to be careful, the living conditions also decrease over a longer period of time, with perhaps better installations. More research is needed, Santamouris said.

In his daily work he is working on coatings for external surfaces that clearly reduce the temperature. At present, a reduction in surface temperature of 7 to 8 degrees is possible, which leads to a fall in ambient temperature of around 3.5 degrees. The (expected) target is 15 and 3.8 respectively. Also coatings that change color depending on the temperature are in the making, and even a coating in the form of an easy to apply spray (‘photonic spray’), which should lead to a roof temperature that is 10 degrees lower.

Increasing cooling load, reinforced by the Urban heat island effect, will become a much bigger problem than thought, at least as I thought. It is one of the potential runaway effects in the climate crises. So, get rid of hard pavements, use covers to shadow streets (Velo’s and Tolda’s as often in southern Spain) ), and green everything that is possible: in the form of trees, I would say. We already needed trees in large amounts anyway, that is, as CO2 compensation, shadow supplier, biobased material supply and as food forests. Count your winnings. Trees it is.



picture on home page: https://www.princeton.edu/news/2019/09/04/solutions-urban-heat-differ-between-tropical-and-drier-climes