Urban growth, heat islands, humidity: the cost of climate change is multiplying in tropical cities

Manila. Image: Getty.

Some 60 per cent of the planet’s expected urban area by 2030 is yet to be built. This forecast highlights how rapidly the world’s people are becoming urban. Cities now occupy about 2 per cent of the world’s land area, but are home to about 55 per cent of the world’s people and generate more than 70 per cent of global GDP, plus the associated greenhouse gas emissions.

So what does this mean for people who live in the tropical zones, where 40 per cent of the world’s population lives? On current trends, this figure will rise to 50 per cent by 2050. With tropical economies growing some 20 per cent faster than the rest of the world, the result is a swift expansion of tropical cities.

Population and number of cities of the world, by size class, 1990, 2018 and 2030. Image: World Urbanization Prospects 2018, United Nations DESA Population Division.

The populations of these growing tropical cities already experience high temperatures made worse by high humidity. This means they are highly vulnerable to extreme heat events as a result of climate change.

For example, extremely hot weather overwhelmed Cairns last summer. By December 3 2018, the city had recorded temperatures above 35°C nine days in a row. Four consecutive days were above 40°C.

Cairns’ heatwave summer. Image: authors, using BOM temperature data.

For our research, temperature and humidity sensors were strategically placed in the Cairns CBD to represent people’s experience of weather at street level. These recorded temperatures consistently higher than the Bureau of Meteorology (BoM) recordings, reaching 45°C at some points.

Highest temperatures recorded by James Cook University weather data sensors during the November-December 2018 heatwave in Cairns. Image: Bronson Philippa/author provided.

Local effects magnify heatwave impacts

Urban environments in general are hotter than non-urbanised surroundings that are covered by vegetation. The trapping of heat in cities, known as the urban heat island effect, has impacts on human health, animal life, social events, tourism, water availability and business performance.

The urban heat island effect intensifies the impacts of increasing heatwaves on cities as a result of climate change.

Projections of increased heatwave frequency for Cairns region using visualisation platform on Queensland Future Climate Dashboard. Image: Queensland Future Climate Dashboard/Queensland Government.

But it is important to remember that other local factors also influence these impacts. These include the scale, shape, materials, composition and growth of the built environment in a particular location and its surrounding areas.

The differences between the BoM data recorded at Cairns airport and the inner-city recordings show the impacts of urban expansion patterns, built form and choice of materials in tropical cities.

The linear layout of Cairns has, on one hand, enabled the formation of attractive places for commercial activities. As these activity centres evolve into focal points of urban life, they in turn influence all sorts of socioeconomic parameters.

On the other hand, the form the built environment takes changes the patterns of wind, sun and shade. These changes alter the urban microclimate by trapping heat and slowing or channelling air movements.

The layout and structures of Cairns CBD alter local microclimates by trapping heat and altering air flows. Image: State of Queensland 2019.

Shifting the focus to the tropics

To date, a large body of research has explored the undesired consequences of climate change and urban heat islands. However, the focus has been on capital and metropolitan cities with humid continental climates. Not many studies have looked at the economic and social impacts in the tropical context, where hot and humid conditions create extra heat stress.

Add the combined effects of climate change and urban heat islands and what are the socio-economic consequences of heatwaves in a tropical city like Cairns? We see that climate change adds another dimension to the relationship between cities, economic growth and development.

This presents a huge opportunity to start thinking about building cities that are not superficially greenwashed, but which instead tackle pressing issues such as climate variability and create sustainable business and social destinations.

In cold climates, heatwaves and urban heat islands are not necessarily undesired, but their negative impacts are more obvious and harmful in warmer climates. And these harmful impacts of heatwaves on our economy, environment and society are on the rise.

We have scientific evidence of the increasing length, frequency and intensity of heatwaves. The number of record hot days in Australia has doubled in the past five decades.

Projections of changes in heatwave frequency for northern Queensland in 2030 and 2070. Image: Queensland Future Climate Dashboard/Queensland Government.

What are the costs of heatwaves?

Increased exposure to heatwaves amplifies the adverse economic impacts on industries that are reliant on the health of their outdoor workers. This is in addition to the extreme heat-related fatalities and health-care costs of heatwave-related medical emergencies. As a PwC report to the Commonwealth on extreme heat events stated:

Heatwaves kill more Australians than any other natural disaster. They have received far less public attention than cyclones, floods or bushfires — they are private, silent deaths, which only hit the media when morgues reach capacity or infrastructure fails.

Heat also has direct impacts on economic production. A 2010 study found a 1°C increase resulted in a 2.4 per cent reduction in non-agricultural production and a 0.1 per cent reduction in agricultural production in 28 Caribbean-basin countries. Another study in 2012 found an 8 per cent weekly loss of production when the temperature exceeded 32°C for six days in a row.

The 2017 Farm performance and climate report by the Australian Bureau of Agricultural and Resource Economics and Sciences (ABARES) states:

The recent changes in climate have had a significant negative effect on the productivity of Australian cropping farms, particularly in southwestern Australia and southeastern Australia.

Average climate effect on productivity of cropping farms in southwestern and southeastern Australia since 2000–01 (relative to average conditions from 1914–15 to 2014–15). Image: Farm performance and climate, ABARES.

It’s not just farming that is vulnerable. A Victorian government report report this year estimated an extreme heatwave event costs the state’s construction sector A$103 million. The impact of heatwaves on the city of Melbourne’s economy is estimated at A$52.9 million a year on average.

Impacts of heatwaves on Victoria’s main economic sectors. Image: State of Victoria Department of Environment, Land, Water and Planning.

According to this report, economic costs increase exponentially as the severity of heatwaves increases. This has obvious implications for cities in tropical regions.

As the next step in our research, we are examining the relationship between local urban features, urban heat islands, the resulting city temperatures and their direct and indirect (spillover) effects on local and regional economic activities.

Taha Chaiechi, Senior Lecturer, James Cook University and Silvia Tavares, Lecturer in Urban Design, James Cook University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.


 

 
 
 
 

London’s rail and tube map is out of control

Aaaaaargh. Image: Getty.

The geographical limits of London’s official rail maps have always been slightly arbitrary. Far-flung commuter towns like Amersham, Chesham and Epping are all on there, because they have tube stations. Meanwhile, places like Esher or Walton-on-Thames – much closer to the city proper, inside the M25, and a contiguous part of the built up area – aren’t, because they fall outside the Greater London and aren’t served by Transport for London (TfL) services. This is pretty aggravating, but we are where we are.

But then a few years ago, TfL decided to show more non-London services on its combined Tube & Rail Map. It started with a few stations slightly outside the city limits, but where you could you use your Oyster card. Then said card started being accepted at Gatwick Airport station – and so, since how to get to a major airport is a fairly useful piece of information to impart to passengers, TfL’s cartographers added that line too, even though it meant including stations bloody miles away.

And now the latest version seems to have cast all logic to the wind. Look at this:

Oh, no. Click to expand. Image: TfL.

The logic for including the line to Reading is that it’s now served by TfL Rail, a route which will be part of the Elizabeth Line/Crossrail, when they eventually, finally happen. But you can tell something’s gone wrong here from the fact that showing the route, to a town which is well known for being directly west of London, requires an awkward right-angle which makes it look like the line turns north, presumably because otherwise there’d be no way of showing it on the map.

What’s more, this means that a station 36 miles from central London gets to be on the map, while Esher – barely a third of that distance out – doesn’t. Nor does Windsor & Eton Central, because it’s served by a branchline from Slough rather than TfL Rail trains, even though as a fairly major tourist destination it’d probably be the sort of place that at least some users of this map might want to know how to get to.

There’s more. Luton Airport Parkway is now on the map, presumably on the basis that Gatwick is. But that station doesn’t accept Oyster cards yet, so you get this:

Gah. Click to expand. Image: TfL.

There’s a line, incidentally, between Watford Junction and St Albans Abbey, which is just down the road from St Albans City. Is that line shown on the map? No it is not.

Also not shown on the map: either Luton itself, just one stop up the line from Luton Airport Parkway, or Stansted Airport, even though it’s an airport and not much further out than places which are on the map. Somewhere that is, however, is Welwyn Garden City, which doesn’t accept Oyster, isn’t served by TfL trains and also – this feels important – isn’t an airport.

And meanwhile a large chunk of Surrey suburbia inside the M25 isn’t shown, even though it must have a greater claim to be a part of London’s rail network than bloody Reading.

The result of all these decisions is that the map covers an entirely baffling area whose shape makes no sense whatsoever. Here’s an extremely rough map:

Just, what? Image: Google Maps/CityMetric.

I mean that’s just ridiculous isn’t it.

While we’re at it: the latest version shows the piers from which you can get boats on the Thames. Except for when it doesn’t because they’re not near a station – for example, Greenland Pier, just across the Thames to the west of the Isle of Dogs, shown here with CityMetric’s usual artistic flair.

Spot the missing pier. You can’t, because it’s missing. Image: TfL/CityMetric.

I’m sure there must be a logic to all of this. It’s just that I fear the logic is “what makes life easier for the TfL cartography team” rather than “what is actually valuable information for London’s rail passengers”.

And don’t even get me started on this monstrosity.

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and on Facebook as JonnElledgeWrites.