FLASH FLOODS

Recently, cloudbursts have been reported from several places in India.

Important points:

• Cloudbursts are short-duration, intense rainfall events over a small area.
• It is a weather phenomenon with unexpected precipitation exceeding 100mm/h over a geographical region of approximately 20-30 square km.
• In the Indian Subcontinent, it generally occurs when a monsoon cloud drifts northwards, from the Bay of Bengal or the Arabian Sea across the plains then on to the Himalaya that sometimes brings 75 millimetres of rain per hour.
• The relative humidity and cloud cover is at the maximum level with low temperature and slow winds because of which a high amount of clouds may get condensed at a very rapid rate and result in a cloudburst.
• 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.
• Rain is condensed water falling from a cloud while cloudburst is a sudden heavy rainstorm.
• Rain over 100mm per hour is categorised as a cloudburst.
• The cloudburst is a natural phenomenon, but occurs quite unexpectedly, very abruptly, and rather drenching.

Impact:

• Several studies have shown that climate change will increase the frequency and intensity of cloudbursts in many cities across the globe.
• In May 2021, the World Meteorological Organization noted that there is about a 40% chance of the annual average global temperature temporarily reaching 1.5°C above the pre-industrial level in at least one of the next five years.
• It added that there is a 90% likelihood of at least one year between 2021 and 2025 becoming the warmest on record and dislodge 2016 from the top rank.
• It is seen that more cloudbursts are happening in Himalayan region because the decadal temperature rise in the Himalayan region is higher than the global rate of rising temperatures.

Consequences

Flash floods.

• There is no satisfactory technique for anticipating the occurrence of cloud bursts because they develop over a small period of time.
• A very fine network of radars is required to be able to detect the likelihood of a cloud burst and this would be expensive.
• Only the areas likely to receive heavy rainfall can be identified on a short range scale. Much of the damage can be avoided by way of identifying the areas and the meteorological situations that favour the occurrence of cloud bursts.

SOURCE: THE HINDU,THE ECONOMIC TIMES,MINT