Frequency of Cloudbursts
Source: By Aswathi Pacha: The Indian Express
Recently, at least seven people were killed, 17 injured and over 35 missing after a cloudburst hit a remote village of Jammu and Kashmir. Recently, cloudbursts have been reported from several places in J&K, Union Territory of Ladakh, Uttarakhand and Himachal Pradesh. A 2017 study of cloudbursts in the Indian Himalayas noted that most of the events occurred in the months of July and August.
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.
A study published last year studied the meteorological factors behind the cloudburst over the Kedarnath region. They analysed atmospheric pressure, atmospheric temperature, rainfall, cloud water content, cloud fraction, cloud particle radius, cloud mixing ratio, total cloud cover, wind speed, wind direction, and relative humidity during the cloudburst, before as well as after the cloudburst. The results showed that during the cloudburst, the relative humidity and cloud cover was at the maximum level with low temperature and slow winds. “It is expected that because of this situation a high amount of clouds may get condensed at a very rapid rate and result in a cloudburst,” write the team.
Several studies have shown that climate change will increase the frequency and intensity of cloudbursts in many cities across the globe. In May, 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.
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. Also, there is evidence suggesting that globally short duration rainfall extremes are going to become more intense and frequent. With warming climate or climate change, we will surely witness these cloudburst events in increased frequency in the future.
Can we predict cloudbursts?
That’s an extremely challenging task and is very difficult to model cloudburst, says Subimal Ghosh from the Department of Civil Engineering at IIT Bombay. His team has been studying the Indian monsoon and hydro-climatic extremes.
He adds that models do not really work at that resolution and explains in detail with the example of popcorn. “Imagine you are making popcorn. The cooking pot heats up and the corn pops. If I ask you which corn will pop first, you may not be able to answer. You need very fine resolution studies to decode. Also, if I ask you how much corn will pop after two minutes, you will be able to say 99%. But what about how many after 10 seconds? The answer is difficult for finer resolution and finer timescale. Similarly, for hourly rainfall and cloudbursts, it is very difficult to simulate the intensity and location.”
