INTERACTIVE: Hotter cities, heavier storms

By SHYAFIQ DZULKIFLI 

PETALING JAYA: The hotter it gets, the harder it rains. In urban areas such as the Klang Valley, experts say this is increasingly the reality. 

They say rising temperatures, combined with rapid development and climate change, are intensifying thunderstorms, increasing the risk of flash floods in cities. 

One reason for the rising heat is the Urban Heat Island (UHI) effect. This occurs when cities replace green areas with pavement, buildings, and other surfaces that absorb and retain warmth. 

This leads to significantly higher temperatures in cities compared to surrounding areas. The hotter air rises to form clouds, leading to heavy downpours that can cause floods. 

“In urban areas, concrete buildings, asphalt and other man-made structures absorb heat faster than surrounding areas, creating pressure differences that lead to low-level convergence. 

“Hotter conditions in the city make the air more buoyant, and buildings of varying heights can induce turbulence that helps air rise,” said Climatologist Professor Emeritus Fredolin Tangang from Universiti Kebangsaan Malaysia. 

He said the UHI effect plays a role, but is not the sole factor, behind heavy rains that led to flash floods in Kuala Lumpur and other parts of the Klang Valley over the past month. 

Tangang said thunderstorms are common during inter-monsoon periods from April to May and September to October, when weaker winds create favourable conditions for them to develop. 

Climate change is also a key factor driving the trend. 

“Global warming increases the amount of moisture in the atmosphere, which over time intensifies thunderstorms in major cities, including Kuala Lumpur,” said Tangang. 

He said a study has shown that extreme rainfall intensity in Kuala Lumpur has gone up threefold over the past 30 years, a trend closely linked to the rising incidence of flash floods in recent years. 

Urban flooding has also been recorded even during drier climate phases.  

Scroll through past The Star reports below on flash flood events during dry years. 

Meteorologist Professor Emeritus Azizan Abu Samah said the Klang Valley is currently experiencing conditions in which warmer atmospheric temperatures allow more moisture to be held in the air, increasing the potential intensity of thunderstorms. 

“At present, if you have a warmer atmosphere, it can hold more water vapour, so thunderstorms become stronger and rainfall intensity increases, raising the risk of flash floods,” he said. 

He said the UHI effect may also contribute to stronger localised thunderstorms, as urban areas are generally warmer than surrounding rural regions. 

Both experts cautioned that climate change is increasing the intensity of extreme rainfall events.

Tangang said that for every 1°C rise in temperature, the atmosphere can hold about 7% more moisture, which can fuel heavier rainfall events. 

Azizan cited findings from the Intergovernmental Panel on Climate Change (IPCC), which suggest that the increasing trend in high-intensity rainfall events in Malaysia could be due to climate change. 

He added that urban floods are linked not only to rainfall intensity but also to drainage capacity and land-use changes. 

“Heavy rainfall can cause flash floods if drainage systems are not well designed in certain areas. Soil erosion and sedimentation can also clog drains and worsen flooding,” he said. 

He stressed that urban planning must take into account the increased runoff from development projects. 

“If you build a township or high-rise, you increase runoff in that area. The question is whether the drainage system is sufficient and where that extra water will go,” he said. 

To mitigate the UHI effect, Tangang called for greener cities through increased tree planting, restoration of water bodies and wetlands, as well as the use of reflective or “white” roofs. 

Azizan said Malaysia needs more climate-resilient urban planning that integrates infrastructure, drainage and environmental considerations. 

“We need to be weather and climate-wise in building design and urban planning, adopting an integrated approach instead of relying on quick technological fixes,” he said. 

In a recent interview with StarMetro, Minister in the Prime Minister’s Department (Federal Territories) Hannah Yeoh said measures were being taken to turn Kuala Lumpur into a “sponge city” to deal with the record rains. 

This would mean, among others, having more green areas, increasing on-site detention ponds, and considering incentives for developers to include green spaces in their projects. 

“The existing infrastructure was designed for historical rainfall patterns, and the intense rainfall we are experiencing now means that traditional capacity is being overstretched. 

“That means we should start building infrastructure with greater capacity,” Yeoh said in the interview.