Trees or paint?

Bring on Permaculture design

It can be fun sometimes, following the research, because it can be contradictory. A lot depends on the research parameters and what the researchers choose to include, exclude, eliminate and study. In this case I’m looking at research about the so-called cool-roofs and how they can reduce building cooling needs. Is it better to use vegetation or reflective ‘smart’ paint?

Some people at University College London concluded that painted roofs are the way to go. They used the heatwave of 2018 as a basis for the research and they showed that air-conditioning units would have raised outdoor temperatures by 0.5°C for the whole of London and 1°C for the dense city centre. Not the way to go then. Green roofs and ground-level vegetation would lower outdoor temperatures by a negligible 0.3°C but painted reflective roofs would lower the temperature by, on average 1.2°C and 2°C in some areas.

The results came from a computer model they had set up.

Some other researchers at the University of Exeter set up their own model and it showed that painting the roofs would have lowered temperatures by, on average, 0.8°C. This, they reckon, could have saved 249 people from dying from the heat.

Across the water from London, some researchers at the University of Texas at Austin were looking at the same question. Their model showed that, for a generic city block, painting the roofs white was better than planting trees. So good so far, everyone seems to be agreeing with each other. Except …. the cunning researchers in Texas added another parameter into their model. They fed in the social vulnerability index that had already been developed by the U.S. Centers for Disease Control and Prevention.

This index considers factors like minority status and socio-economic status, the composition of households, housing types, and access to transportation networks. Low vulnerability means the neighbourhood is inhabited by people with good incomes, good housing in good condition, easy transport access etc. High vulnerability means the opposite.

This vulnerability index changed everything. The Texas model then showed that painting roofs was the best strategy for low vulnerability areas but planting trees was best for the high vulnerability areas. Another great example of the ‘there is no one size fits all solution’ principle.

Some other cunning researchers at Arizona State University decided to study what have been fatuously called ‘smart streets’. These are ones that have been covered with a reflective surface, the idea being that if you reflect light away you reduce urban heating. Now this seems a good idea, when the sun hits dark tarmac it heats it up, if it hits a shiny surface a lot of the sunlight will get reflected back out. Except, as the researchers point out, there are people hanging around on the streets, working, walking their dogs, or sitting chatting. They are already being heated up by the incoming sunshine and with a smart street they are now getting additional heat bounced onto them from the reflective surface. This isn’t very good. The researchers found that a shiny surface over the asphalt lowered the surface temperature by up to 6°C which seems great, but the same surface raised the radiant heat over the surface by 4°C when compared to uncoated asphalt.

As it’s something we need to hear more I would like to quote V. Kelly Turner, assistant professor of urban planning at UCLA and co-author of the study. "The solutions are context-dependent and depend on what you want to achieve." Yes!!! They all are, from agriculture through housing to dietary regimes. The latter is up close and personal, if you feed me lentils and chickpeas I have to put rocks in my pockets to stop myself floating away. It’s time we had a new dietary category which I chose to name ‘flatulants’.

Bring in Permaculture

We’ve got the above data and we can now put it through the Permaculture design process. For a start we can turn to the ethics, smart paint may improve things for people but the manufacturing of these paints doesn’t ‘care for the Earth’. Their production is environmentally destructive.

We can then pass on to the design principles. For example ‘each element in a system should have more than one function.’ Smart paints do one job, trees and vegetation can be designed to produce a wide range of benefits. These range from shade through fruit and nut production to reducing crime levels. In fact the benefits of trees in urban areas are numerous and this means that a designer would virtually always choose trees over paint. That said in some extreme contexts it may be necessary to use both. In this case, the ecological costs of the paint production are outweighed by the social benefits. My opinion would be that these cases would be fairly rare.

This shows the strength of Permaculture design. Researchers spend time removing non-causative correlations and extraneous parameters and give us some relatively ‘clean’ data. We take that data and then add parameters back in to give ourselves a holistic view which we then use to design a system that cares both for people and the Earth.