Successful Greening: The Warning Effects Of Urban Heat Islands

In March, Think City published the results of a land surface which revealed marked increases in the peak land surface temperatures of five Malaysian cities over several decades. The links between increases in temperature, climate change and urban expansion are well established, as is the challenge they pose for the liveability of cities, human health and urban wildlife.

As part of Think City’s mission to democratize data and make climate information more accessible, the results are displayed as temperature maps – dynamic, interactive data visualizations – which are accessible through its Urban Analytics portal.

The study observed land surface temperatures in the Kuala Lumpur city centre, Bayan Lepas, George Town, Johor Bahru and Ipoh and the results of the urban heat island effects created by the urban heat island effect is caused by the types of materials used in cities such as concrete and bitumen, which absorb and re-emit the sun’s heat more than natural landscapes. 

The maps record a consistent increase across all five locations. The rise in temperature in urban areas has been linked primarily to the urban heat island effect, the lack of greenery and global warming. Two characteristics are clearly evident. Firstly, Malaysian cities are getting hotter due to the increasing intensity of development, which is compounded by the effects of climate change. Secondly, the maps show that urban greening had beneficial impacts, with the ability to lower urban temperatures between two and eight degrees Celsius. 

The Citymaker spoke to Dr. Ceelia Leong, Geospatial Analyst at Think City, about the study and its results, the urban heat island effects and the growing importance of geospatial data in shaping public policy frameworks.

Can you explain the concept of land surface temperature and tell us about this new Think City study?

Ceelia Leong: In layman’s terms, land surface temperature is how hot the land is.  It’s important to monitor this heat or land surface temperature because the warmth rising from the earth affects our weather and climate patterns. [The study] is part of [Think City’s] climate response effort.  We want to raise awareness and educate communities by sharing our findings and insights for them. We are identifying solutions and assisting communities in adapting to extreme weather conditions.

We chose major cities with a high population [that] have experienced a number of changes over the years. [We wanted] to get a snapshot of what is going on in these cities. The different timeframes [we used] is not deliberate. In order to produce these maps, we work with satellite images, and the satellite images are prone to atmospheric disturbance, like clouds and haze, and this affects the analysis. It’s something that we cannot control, but what we can do is to look for the closest, clearest and available good data that [will give us] a reliable analysis.  

Our analysis incorporates two time periods where there’s good quality data available to compare the temperature difference. It’s important to note that there is a limitation of having sufficient data points. You need many data points to get annual mean temperature and observed increase over a long time period. What we’re doing here actually is [giving] a snapshot of what the cities have experienced over several decades, which we visualize to communicate it effectively and powerfully to the public. That’s why we’re using [interactive] maps where you can glide between the two different time period to see how hot it has become in certain part of the cities.

Did you identify clear reasons for these temperature increases?

Ceelia Leong: The most important is that we see a consistent increase in temperature across the five cities. There are two characteristics that are clearly evident. First, that Malaysian cities are getting hotter due to increasing intensity of development. This is compounded by the effects of climate change. 

Second, the maps also show the beneficial impacts of urban greening, which can lower urban temperatures between two to eight degrees. We also found out that…[though]….the geographical characteristics of the cities are all different, the temperature increases are primarily due to the urban heat island (UHI) effect, [through] a lack of greenery and also global warming.

To anyone coming across the concept of the urban heat island effect for the first time, the term actually means that an urban area becomes warmer than the rural areas surrounding it. This happens when we replace the natural landscape, for example, greenery, with materials that absorb, retain, or re-emit the sun’s heat. For example, like concrete and asphalt, materials [that are] widely used in buildings, pavements, and roads.

What particularly stuck out for you from the study’s findings?

Ceelia Leong: The results in general were what we expected, [in terms of] the temperature increases. You can view this on the Urban Analytics Portal. The highest temperature rise that we see is Ipoh, about a 6.75°C increase, and that’s followed by Johor Bahru, at 6.7°C, and George Town not too far behind at 6.37°C. Then Bayan Lepas slightly lower, at 5.63°C.

Surprisingly KL City Centre is about a 1.64°C rise. It did increase, but it’s a smaller increase. When compared to the other cities [in the study], we found that KL City Centre is able to demonstrate [the need for] efficient, urban greening as a coolant. It has domestic gardens, parks and woodlands. When we looked deeper, we found that there is greenery around the city, like the KL Forest Eco Park, the Perdana Botanical Garden, [and other] gardens and public spaces. These help to explain the smaller increase in temperature. 

However, it’s important to note that this does not reflect temperature change in greater-KL, which is a much bigger area. The urban development has expanded from KL City Centre to other areas, satellite cities, and so forth, over the years. So, when we expand and analyze a bigger area, we’re going to see some difference in temperature.

Would you expect similar results in other cities and urban centres in Malaysia that weren’t included in the study?

Ceelia Leong: Yes. If you’re replacing the natural landscape with materials that retain and absorb heat, you will see this increase in other cities as well. Unless they use practices similar to KL City Centre, where you have more greenery, you may see a similar pattern.

Visualization – the use of interactive maps – is a key component of the study. Does this approach lend itself to making those maps dynamic? Something we can expect to be periodically updated?

Ceelia Leong: We would definitely like to update the data as part of our climate monitoring activities. As we expand to more cities and [expand those timeframes] the better we will be able to see the changes. 

The methodology used for the study, GIS or geographic information systems, may not be one that everyone is familiar with. Can you explain the GIS approach to modelling data?

Ceelia Leong: We used remote sensing technology, which is satellite imagery, to map the extent of the heat island effect in Malaysian cities. We used free and open-source imagery provided by United States Geological Survey (USGS). This fits into our GIS data model, where we process and combine different parameters of surface energy to calculate the surface temperature.

The surface of the year radiates thermal energy in a thermal infrared part of the spectrum. The energy radiated is proportionate to the temperature. Therefore, we can calculate the land surface temperature from there. 

And. if you’re wondering what some of the parameters of surface energy that we take into consideration [to make] those calculations are: they include the Top of Atmosphere Reflectance (TOA), the brightness temperature, thermal emissivity and vegetation health data.

How does this approach give us a deeper insight or understanding of the data?

Ceelia Leong: GIS is an extremely visual tool. And it’s powerful [because of] the way you can convey information to the public. There are many studies on climate change and temperature increase but they aren’t necessarily easy to digest or understand. Through our Urban Analytics Portal and the use of [data visualizations like] mapping, it can help to effectively convey [that information] to people. To [enable them] to visualize the [scale of temperature increases in different parts of their cities] and how greening and different [construction] materials play a role in [determining] heat in the city centre. Which helps to raise awareness and educate communities.

Does the visual aspect also make it easier to engage policymakers and shape policy?

Ceelia Leong: It’s extremely important to have evidence-led studies to help policymakers formulate strategic policies. The study has caused a [stir]. The Perak Menteri Besar stated that one of the state government’s initiatives is to lower the urban heat island effect. They hope to balance and counter the heat by planting 1 million trees in the state by 2030. They also understand that by felling trees and clearing land for development has contributed to the increase in temperature.

This is an example of how this kind of study can make an impact on policymakers and on the state itself. 

This is an edited version of a conversation that took place on the Reflexive City podcast. 

You can also listen to Dr. Ceelia Leong discuss the report on BFM89.9.