- Title: EXPLAINER: What is a cloudburst and why is it so dangerous?
- Date: 7th August 2025
- Summary: (SOUNDBITE) (English) EMERITUS PROFESSOR OF SCHOOL OF ENERGY AND ENVIRONMENT, CITY UNIVERSITY OF HONG KONG, JOHNNY CHAN, SAYING: “A cloudburst is very simply a burst of rain. So why is it called a burst? Because a lot of water is coming down from the sky in a relatively short period of time. So, for example, in 10 minutes or 20 minutes, when you have lots of water coming d
- Embargoed:
- Keywords: India cloudburst floods global warming landslides weather
- Location: BHATWADI, UTTARAKHAND, INDIA; HONG KONG AND BEIJING, CHINA
- City: BHATWADI, UTTARAKHAND, INDIA; HONG KONG AND BEIJING, CHINA
- Country: China
- Topics: Asia / Pacific,Disaster/Accidents,Floods
- Reuters ID: LVA001559307082025RP1
- Aspect Ratio: 16:9
- Story Text: WHAT IS A CLOUDBURST?
A cloudburst is an intense and sudden downpour. It's called a "burst" because a large amount of rain falls in a very short period—often within 10 to 20 minutes. Since this sudden deluge originates from clouds, it's aptly named a cloudburst.
WHAT CAUSES A CLOUDBURST?
When warm, moist air rises rapidly, the water vapour condenses into large droplets and eventually forms ice. This process creates storm clouds. When a large amount of moisture accumulates in the cloud, it can be released suddenly as heavy rainfall over a short period—making it appear like a “burst.” That’s why it’s called a cloudburst—a rapid, concentrated downpour from a storm cloud.
WHAT MAKES A CLOUDBURST SO FEROCIOUS?
In mountainous regions, the terrain itself helps push air upward. When air masses collide with a mountain, they are forced to rise—this process is known as orographic forcing. Combined with surface heating, this upward motion intensifies, leading to the rapid development of strong storms. As a result, the rainfall can be especially heavy.
This intense downpour often causes flash floods, as rivers and drainage systems cannot handle the sudden volume of water. Additionally, many of these areas suffer from deforestation. Trees play a crucial role in anchoring topsoil; when they are removed, the soil becomes loose and unstable. So, when heavy rain hits, the unprotected topsoil is easily washed away, leading to landslides.
WHY ARE HEAVY RAINFALL EVENTS BECOMING MORE FREQUENT?
The increasing frequency of heavy rainfall is largely driven by global warming, which allows the atmosphere to hold more water vapour. When this moisture is eventually released, it results in more intense rainfall events.
On a regional level—particularly in urban areas—city structures absorb and retain heat, human activities add to local warming, and air pollution increases the number of particles that aid cloud formation. These factors combined make cities, especially megacities, more prone to heavy rain.
CAN WE PREDICT HEAVY RAINFALL EVENTS?
Predicting heavy rainfall is challenging and most weather centres rely on a technique called now-casting to predict short-term heavy rain. This involves analysing current weather conditions to forecast what might happen over the next few hours. While short-term forecasts are limited, we do know that the likelihood of heavy rainfall is increasing over the long term. This calls for proactive planning and the implementation of strategies to reduce the risk of flooding and related impacts.
(Production: Joyce Zhou, Bhushan Kumar, Xiaoyu Yin, Phyllis Xu) - Copyright Holder: FILE REUTERS (CAN SELL)
- Copyright Notice: (c) Copyright Thomson Reuters 2025. Open For Restrictions - http://about.reuters.com/fulllegal.asp
- Usage Terms/Restrictions: None