INTERACTIVE: Hotter cities, stronger storms

By SHYAFIQ DZULKIFLI

PETALING JAYA: Rising urban temperatures in the Klang Valley are contributing to heavier downpours and flash floods, with experts pointing to the Urban Heat Island (UHI) effect as one of the factors intensifying storms.

Experts say the interaction between urban heat, rapid development and climate change is intensifying thunderstorms over densely built-up areas, including the Klang Valley.

Climatologist Professor Emeritus Fredolin Tangang from Universiti Kebangsaan Malaysia said the UHI effect plays a contributing role but is not the sole factor behind the increasing frequency of heavy downpours in urban areas.

“The answer is yes, but UHI is not the only factor,” he said, explaining that thunderstorms are more common during inter-monsoon periods in April to May and September to October, when weaker winds create favourable conditions for thunderstorms to develop.

He said heat and moisture are key ingredients for thunderstorm formation and that urban areas tend to amplify both.

“In urban areas, concrete buildings, asphalt and other man-made structures absorb heat and warm 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,” he said.

Tangang said 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,” he said.

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

Urban flooding has been recorded even during drier climate phases. 

Scroll through past The Star reports 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 also 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 flash 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 in an integrated approach instead of relying on quick technological fixes,” he said.