The phenomenon of cloudbursts

This year’s monsoon season has seen a spate of cloudbursts over the Western Himalayas and the west coast, revealing the deadly, unpredictable face of monsoon rains.

What are cloudbursts?

• Cloudbursts are short-duration, intense rainfall events over a small area.
• According to the India Meteorological Department (IMD), it is a weather phenomenon with unexpected precipitation exceeding 100mm/h over a geographical region of approximately 20-30 square km.
• Areas prone to cloudburst:Cloudbursts do occur at plains, however, mountainous regions are more prone to cloud bursts due to topography. They also occur in desert and in interior regions of continental landmasses.

Occurrence

• Generally cloudbursts are associated with thunderstorms. The air currents rushing upwards in a rainstorm hold up a large amount of water.
  • Air current is air moving from an area of high pressure to an area of low pressure.
• If these currents suddenly cease, the entire amount of water descends on to a small area with catastrophic force all of a sudden and causes mass destruction.
  • This is due to a rapid condensation of the clouds.

Himalayan vulnerability to natural disasters

• The geography of a placemakes it vulnerable to cloudbursts—which are a convective phenomenon producing sudden high-intensity rainfall over a small area.
• Due to its topography, geology, propensity for tectonic activity and ecological fragility, the Himalayan region becomes prone to rapidly changing weather at micro-levels.

How cloudburst is different from rainfall?

• A cloudburst is different from rain only in the amount of water that pours down on the earth.
• The India Meteorological Department (IMD) labels rainfall over 100 mm per hour as cloudburst.
• In simpler terms, if 10 centimetres rainfall is received at a station in one hour, the rain event is termed as cloudburst. 
  • Usually small areas – anywhere between 20-80 square kilometres are affected.

How anthropogenic factors are increasing the events?

• In recent years, the following anthropogenic factors have been implicated in extreme weather events in the Himalayas-
  • Population
  • Deforestation
  • Land-use change
  • Emissions due to urbanization

How climate change is adding to the issue?

• As per the Intergovernmental Panel on Climate Change (IPCC), glaciers in the Himalayas are receding faster than in any other mountain range.
• Glacial lakes formed by melting glaciers are constrained by ice dams.
• Since the Indian summer monsoon coincides with the melting of glaciers, ice dams are weakened by the additional stress of the monsoons and are prone to bursting.
• A flash flood in Kargil in May 2016 was attributed to this.
• As temperatures increase the atmosphere can hold more and more moisture and this moisture comes down as a short very intense rainfall for a short duration probably half an hour or one hour resulting in flash floods in the mountainous areas and urban floods in the cities.

Given the current situation, the planet is surely going to witness cloudburst events in increased frequency in the future.