Turning up the heat on city planners

Published by Flemmich Webb on

By Garry Booth

Madrid’s climate could resemble that of Marrakech in 30 years’ time, while London will experience the sort of summer conditions that residents of Barcelona are accustomed to today. This is the finding of new research by the Crowther Lab, whose environmental scientists tested the extent to which cities around the world are likely to be affected by climate change.

By analysing 520 major cities, the scientists examined to what extent the climate of a particular city in a particular bioclimatic region in 2050 would resemble the climate of cities in different bioclimatic regions today.

Even under an optimistic climate scenario, the researchers found that over three quarters of cities are very likely to experience conditions that are closer to that of another existing city, than their own current climate.

For example, across Europe, both summers and winters will get warmer, with average increases of 3.5˚C and 4.7˚C, respectively. Shifts in rainfall regimes will dominate the tropical cities, characterised by both increases in extreme precipitation events and the severity and intensity of droughts.

The research paper found that as a general trend “all the cities tend to shift towards the sub-tropics, with cities from the Northern hemisphere shifting to warmer conditions, on average circa 1,000 km south and cities from the tropics shifting to drier conditions”.

This means that by 2050, Stockholm’s climate could resemble Budapest’s today, Moscow’s could resemble Sofia’s, Seattle, San Francisco’s and Tokyo, Changsha’s.

Shockingly, the report also found that more than a fifth of the cities studied will experience climate conditions that are not currently experienced anywhere on the planet. Tropical and sub-tropical cities – including Manaus, Kuala Lumpur, Jakarta, and Singapore – are most likely to experience shifts into what the report calls “entirely novel climate regimes”.

Commenting on the report’s findings, Professor Thomas W. Crowther says: “While cities in the northern hemisphere are most likely to experience more dramatic temperature shifts, cities in the tropics may face greater fluctuations in average rainfall. These already ‘hot’ cities are under greater threat of drought and extreme weather events.”

The predicted climatic changes pose big challenges for city planners, businesses and communities, because cities are built for the specific climates they experience. Infrastructure design is based on historical averages of heat, precipitation, freezing temperatures and the most frequent weather events. Even small shifts in average temperatures can have severe consequences for city infrastructure and facilities. In July this year, the French energy company EDF shut down two nuclear reactors at its Golfech nuclear power plant in the southern Tarn-et-Garonne region due to abnormally hot weather in the region.

Soaring temperatures create heightened risks for cities associated with air and water quality, food supply, increased mortality and the spread of diseases, as well as social factors, such as civil disorder.

Lloyd’s City Risk Index shows the scale of the economic cost of extreme temperatures. For example, freeze and heatwave account for $1.2bn of GDP@Risk in the European cities analysed in the index. In Asia, Tokyo, Shanghai, Chongqing, Sydney and Osaka have most GDP at risk from heatwave, the Australian capital regularly breaking high temperature records. New York has the highest GDP at risk ($190m every year) from heatwave of any city in the world, according to the index. Chicago and Dallas are in third position with $76m and $63m respectively.

The long-term trend appears to be that temperatures are rising. According to new data from the World Meteorological Organization and Copernicus Climate Change Programme, the period from 2015 to 2019 is set to be the five warmest years on record. “This year alone, we have seen temperature records shattered from New Delhi to Anchorage, from Paris to Santiago, from Adelaide and to the Arctic Circle,” said UN Secretary-General António Guterres, announcing the data in New York recently.

Europe’s five hottest summers since 1500 have all been in the 21st Century, according to the climatology institute in Potsdam, Germany.

Given the economic and social impacts of temperature extremes, city authorities and planners around the world should take a close look at how well their city is able to withstand the most likely predicted climate scenario, using the data his team collected, Professor Crowther believes. “Not only can these predictions be used to identify potential weaknesses, but it can also be used to inform and improve new development.”

Robert Muir-Wood, Chief Research Officer at modelling company RMS, commended the “analog” approach taken in the study. “The purpose of the [Crowther] research is to make the changes associated with climate change more tangible – for example, to understand the challenges in 2050 for London one could visit and study the current climate in Barcelona,” he commented. “This would include the prevalence of droughts and intense rainfall flash floods, as well as of heatwaves and cold spells.”

In this way, the research helps city planners visualise the climate futures of their respective cities and improve decision-making in terms of climate change.

Some cities are taking the first steps to making themselves more heat resistant in response to rising temperatures.

In Austin, Texas, local laws have been passed that require 50% leaf canopy coverage in all car parks by 2030. Eighty per cent of the trees have to be large shade-producing varieties from a designated list of native shade trees and must be planted within 50ft (15m) of parking spaces. In Los Angeles, city planners are experimenting with the use of light-coloured material for roads rather than heat-absorbing black to make “cool pavements”.

Similarly, climate campaigners in Albuquerque, New Mexico are advocating the use of white-coloured roofs to help mitigate the heat, because the traditional dark roofs can reach temperatures of up to 65C and can be up to 10C hotter than white roofs.

Muir-Wood from RMS says all cities need to understand the scale of the potential changes to their climates ahead and the impact on their economies. “Migration will occur away from cities with intolerable climates,” he says. “It is possible some cities will be abandoned; in others the climate will improve. But preparing for these changes will cost money and planning needs to start now,”

He hopes the research will encourage cities to campaign more vigorously to reduce greenhouse gas emissions. “Cities should take a leadership role,” Muir-Wood says. “They should also educate and prepare their inhabitants for the changes in future climate and what they can do to become more resilient to future climate extremes. Showing what [kind of] city they can expect to become is an excellent way of communicating the changes ahead.”

The wider question posed by the study, however, is whether the political will exists to help cities and their inhabitants adapt quickly enough. If the answer is no, many of the world’s most iconic and celebrated cities could soon be facing an irreversible decline.