Heat Island Effect Can Make Core Of Cities 7 Degrees Hotter: Expert To NDTV

As heat waves increase in India with the rise in global warming, cities are particularly vulnerable because temperatures at the heart of the urban jungles can be as many as seven degrees higher than the areas surrounding them, a leading expert has said.

Speaking exclusively to NDTV on Thursday, Robert Muir-Wood, Chief Research Officer at Moody's RMS - a risk management company - attributed this rise to a phenomenon called the urban heat island effect which, he said, is not only detrimental to productivity but can also cause illness. 

Heat deaths have risen in India in the past decade and, while all metropolises are vulnerable to the heat island effect, the problem is more acute in India, where cities like Mumbai, Delhi, Chennai and Kolkata have a very high population density. Vanishing greenery in the cities has exacerbated the problem, which is likely to get worse as almost 60% of the global population will be living in urban centres in the next 20 years.

The good news, however, is that steps can be taken to mitigate the heating effect, said Mr Muir-Wood, adding that what's needed is a strong city administration that is committed to addressing the problem.

Health Dangers

Listing the main causes of the heat island effect, Mr Muir-Wood said, "So there are three drivers, the first reason is that the surfaces of the buildings, the surfaces of the roads absorb a lot of heat. They tend to be dark materials. They may be glass and concrete, but they absorb a lot of heat. The second reason is that there are lower wind speeds inside a metropolitan area where you have a lot of big buildings. The bigger the buildings, the more they are slowing down the wind."

"The third factor is that there will be a lot of air conditioning plants and other machinery, and cars in the middle of the city, and they are all producing heat too. Depending on how concentrated the population of buildings is, it can drive up the temperatures by five, six or seven degrees centigrade in the heart of the city," he added. 

Pointing out that the difference is the highest in the late afternoons, the research officer said the temperatures in the heart of the city can be dangerous to health and also reduce productivity. 

"It is dangerous, in particular, if you don't have the benefit of air conditioning, (like in) a factory or a building site. In India, the heat wave period may start in March and run through to August. We know that heat waves are getting more intense. They are lasting longer. They are coming earlier. And we know the temperatures are reaching the levels at which they can be dangerous to health," he warned. 

Mr Muir-Wood said the wet bulb temperature, which also takes humidity into consideration, can be dangerous if it gets close to the natural temperature of a human being. 

'Not That Expensive to Act'

To a question on how the urban heat island effect can be mitigated, particularly in the developing world, and the kind of investment doing so would require, the research officer said, "I don't think it is so very expensive to take action to get on top of the problem. Some cities are much better than others. Cities which have a lot of green space within them, including parks and trees, have lower temperatures. I think in Mumbai, there are actions being taken currently, there are attempts to open up lakes. I think there's talk about converting the racecourse into a park and into a forest, even. "

The trouble, Mr Muir-Wood said, is that a lot more money can be made by making a building on a piece of land than planting trees on it. And this, he said, is where a strong city administration can step in to ensure that action is being taken to bring down temperatures for everyone. 

"We do know what to do. It is not that expensive, but it requires a quite strong city government," he said. 

'It Will Be Impossible To Work Outside'

Asked how realistic it is to reduce the heating of cities when urbanisation is going to go up, Mr Muir-Wood said, "It is not only possible, it is really important. Because temperatures are rising and we can measure those increases already. We know already there is evidence of an increase in heat deaths over the past decade compared to the decade before. So this is important, important stuff."

"There are actions that can be taken and those actions are really important. And they simply require strong planning and organisation in cities. If you take no action, the centre of the city will get hotter and hotter. It will become impossible to work outside through the middle of the day because the temperatures will be dangerously high. We use our risk modelling to look out into the future. We do that in order to provide the information that people need to take action today to prevent the worst, the most dangerous, increases of temperature actually happening," he added.