Himachal rains: What are Cloudbursts that killed 56 people? Why are they hard to predict?

This week, Himachal Pradesh has been struck by tragedy, with over 56 lives lost due to cloudbursts and the ensuing landslides. As of Monday, the recovery of 19 bodies has taken place, while concerns linger about individuals trapped beneath the ruins of the fallen Shiva temple in Shimla.

Unrelenting heavy rains since Sunday have unleashed landslides and cloudbursts across Himachal Pradesh. This onslaught has caused roads to be blocked, houses to crumble, and a total of 170 cloudburst and landslide incidents this monsoon season, leading to the destruction of approximately 9,600 houses.

What are Cloudbursts?

A cloudburst describes intense rainfall that suddenly deluges a localized region for a brief period. Though it can manifest in flat terrain, it's most common in hilly landscapes like the Himalayas and the Western Ghats.

Cloudbursts are driven by the convergence of warm monsoon winds and cold air, often catalysed by topography. Yet, not all heavy rainfall qualifies as cloudbursts. For an event to be termed so, there must be 10 cm or more of rain within an hour, covering an area of 100 square kilometres. Even 5 cm of rain in half an hour within the same area meets the criteria.

The magnitude of cloudbursts stands out, as India typically receives around 116 cm of annual rainfall. During these events, a small region can amass about 10% of this annual rainfall in just an hour.

Unpredictability and challenges:

Cloudbursts are notoriously unpredictable, sneaking upon us without warning. With their preference for remote, hard-to-reach areas, these localized phenomena often set off flash floods, endangering settlements downstream.

Predicting cloudbursts remains challenging, especially in the Himalayas' small valleys. Despite the potential assistance of Doppler radar, which gauges velocity information about objects, predicting these events is complex.

Destructive impact and Himachal's vulnerability:

Cloudbursts carry disastrous potential, triggering flash floods capable of uprooting trees, dislodging boulders, and leaving devastation in their wake. As the water surges, it can obliterate structures and trigger landslides in hilly terrain, while in plains, it induces rapid flooding.

In Himachal Pradesh, cloudbursts are not uncommon, especially from June to September during the monsoon. The Himalayan region's distinct geography, wind patterns, and atmospheric temperature gradients contribute to their occurrence. Currently, the monsoon trough is centered over Uttarakhand and Himachal Pradesh, amplifying rainfall activity.

Record-breaking July rains inundated Himachal, claiming over 100 lives in a span of two weeks, making it one of the worst-hit regions. The frequency of cloudbursts is observed to be higher in July and August, with Kullu, Shimla, Kinnaur, and Mandi most susceptible to these unpredictable events.

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