More than two days of torrential rainfall, flash floods, landslides, and lightning claimed the lives of at least 307 people in the mountainous Khyber Pakhtunkhwa region of Pakistan, with many more still missing.
The intensity of the downpour was unprecedented, overwhelming local infrastructure and leaving entire communities in ruin. This tragic event serves as a stark reminder of the destructive power of cloudbursts, intense, localised storms that dump enormous amounts of rain in a short period, causing flash floods and widespread devastation.
What is a cloudburst?
Bazlur Rashid, a meteorologist at the Bangladesh Meteorological Department (BMD), defined a cloudburst as an event that takes place over a small area, typically 30 square kilometres or less, with rainfall exceeding 100 mm per hour.
He said a cloudburst occurs when warm, moist air rises rapidly due to convection or orographic lifting, forming dense cumulonimbus clouds. These clouds trap large amounts of moisture, and once they can no longer hold it, an intense downpour takes place suddenly. When the rainwater can't flow away because rivers, canals, and other water bodies are filled with soil, it often causes flash floods and landslides.
Cloudbursts are most common in mountainous areas, where moist air is forced to rise over the peaks. When moist air moves across a landscape and hits a mountain, it can't move through the mountain, so the air is forced to rise over the top. As it rises, the air cools down, and the moisture in the air condenses to form clouds. If the air is very moist and the conditions are right, this can lead to heavy rainfall or even a cloudburst. The Himalayas, Andes, and Rocky Mountains are examples of regions where this occurs.
Cloudbursts also take place in tropical and subtropical areas like South Asia, especially during the monsoon season, when high humidity and strong air movements create perfect conditions for these intense storms.
The formation of a Cloudburst is influenced by several meteorological factors:
Orographic effect
When moist air hits a mountain slope, it is forced to rise, cool, and condense into dense clouds. Sometimes these clouds get trapped in valleys and, once saturated, release heavy rain suddenly, causing a cloudburst.
Temperature contrast
A sharp difference between warm air at the surface and cold air above creates instability. This makes clouds grow vertically and burst, releasing rain all at once.
Monsoon winds
Moisture-laden monsoon winds carry huge amounts of water vapour. When blocked by mountains or cooled suddenly, the moisture condenses rapidly, sometimes leading to cloudbursts.
Western disturbances
Moist winds from the Mediterranean, known as western disturbances, often mix with monsoon currents. This interaction creates unstable conditions, triggering extreme local downpours.
Topographical trapping
Clouds can get stuck in narrow valleys or rugged terrain. Unable to disperse, they accumulate moisture and eventually discharge it all at once as a cloudburst.
Climate change
Global warming increases the atmosphere's moisture-holding capacity. As a result, rainfall events have become more intense, making cloudbursts more frequent and destructive.
Cloudburst and Bangladesh
Bazlur Rashid has been studying climate change in Bangladesh for over 16 years. His research indicates that Cloudbursts affected the Rangpur region in July 2020, with 447 millimetres of rainfall recorded between the night of 26 September and the morning of 27 September, marking the highest rainfall in the past 70 years.
Cloudbursts also struck Sylhet on 18 June 2022, when 304 millimetres of rainfall inundated the city and surrounding haor areas in just one day. The previous day, Meghalaya, India, upstream of Sylhet, saw 1,004 millimetres of rain, which, combined with the heavy local rainfall, submerged 80% of Sylhet and Sumanganj. These areas usually receive 200-300 millimetres of rainfall during the rainy season.
In the latest Cloudburst event, from 19 to 22 August 2024, Feni recorded 435 millimetres of rainfall, while Cumilla saw more than 557 millimetres, and Noakhali experienced 605 millimetres of rainfall.
Why are cloudbursts a concern?
Cloudbursts are a concern primarily because of their intense and sudden nature. Here's why they pose significant risks:
Heavy rainfall in a short time: Cloudbursts can dump an enormous amount of rain in a very short period, often hundreds of millimetres in just an hour or less. This can overwhelm drainage systems and flood areas that are typically not prone to flooding.
Flash flooding: The sudden surge of water can lead to flash floods, especially in hilly or mountainous regions. These floods can be extremely dangerous, sweeping away homes, roads, and even whole communities in a matter of hours.
Landslides: In mountainous regions, the heavy rainfall from a Cloudburst can trigger landslides, which can block roads, damage infrastructure, and cause loss of life.
Impact on infrastructure: The sudden influx of water can damage infrastructure, especially in urban areas where the ground is often paved and lacks natural drainage. Roads, bridges, and buildings can be severely damaged by the sudden floodwaters.
Agriculture and livelihoods: In rural areas, Cloudbursts can devastate crops and farmland, leading to significant economic losses for farmers who depend on their land for survival.
Challenges in predicting cloudbursts
Forecasting Cloudbursts remains a challenge due to their highly localised nature. Unlike typical weather systems that affect broad regions, Cloudbursts are confined to small areas and can develop quickly, leaving little time for warning.
Modern meteorological tools like satellite imagery and weather radar have helped improve predictions, but accurately forecasting the exact location, intensity, and timing of a cloudburst remains difficult.
Advances in weather modelling and atmospheric research are crucial for improving cloudburst forecasts. However, the unpredictable nature of these events means that communities living in high-risk areas need to be proactive in their disaster preparedness and response strategies.
Conclusion
The recent cloudburst incident is another reminder of the unpredictable nature of these extreme weather events and the vulnerability of mountainous regions to such disasters. As global climate patterns shift, the frequency and intensity of cloudbursts are likely to increase, requiring better forecasting, early-warning systems, and disaster mitigation strategies.
Comments