Cloudbursts are characterized by sudden and intense rainfall occurring over a limited area within a short duration of time. As per the definition provided by the India Meteorological Department (IMD), a cloudburst occurs when there is a rainfall of 100 millimeters within an hour over an area of approximately 20-30 square kilometers. The consequences of cloudbursts can be severe, leading to flash floods, urban floods, landslides, significant soil erosion, leaching, and posing challenges in recharging the water table.
In India, cloudbursts are predominantly observed during the months of July and August, when the southwest monsoon intensifies. However, their frequency is notably higher in the Himalayan region due to the topographical characteristics. The presence of towering mountains in the Himalayas obstructs the movement of monsoon clouds, creating conditions conducive to cloudbursts. Instances of cloudbursts have been recently recorded in regions such as Jammu and Kashmir, Ladakh, Himachal Pradesh, Uttarakhand, and others.
Nonetheless, it is important to note that cloudbursts can occur in any area where favorable conditions exist. For instance, the cloudburst that occurred in Mumbai in July 2005 resulted in a staggering 1,448 mm of rainfall within a span of 10 hours.
The increased frequency of cloudbursts in the Himalayan region can be attributed to various factors, which are as follows:
Orographic lift: Cloudbursts in the Himalayan region are a result of the rapid upward movement of moist air masses caused by steep orography. The warm and humid air is forced to rise due to the presence of mountains. As the air mass ascends, it forms towering vertical columns of clouds known as “cumulonimbus” clouds. Such clouds often trigger heavy and abrupt rainfall accompanied by thunder and lightning. This upward motion of clouds is referred to as “orographic lift.”
Lack of upper air movement: The absence of significant upper air movement at high altitudes hampers the dissipation of moisture, leading to the accumulation of water vapor within the clouds. Consequently, this concentration of moisture eventually results in sudden, localized downpours.
Climate change: The Himalayan region has experienced a higher rate of temperature rise compared to the global average. Numerous studies on climate change in the Himalayas have consistently reported significant warming trends, exceeding the global average temperature rise of 0.4 degrees Celsius. Elevated temperatures contribute to increased moisture levels in the atmosphere, which can manifest as pre-monsoon thunderstorms in the Indo-Gangetic Plains or cloudbursts and hailstorms in mountainous regions like Uttarakhand.
Conclusion:
While the frequency of cloudburst events has been on the rise, their unpredictable nature regarding location and impact further compounds the challenges associated with them.