EXPLAINER: Understanding the 'rain bomb' and cloudburst forecast

Yet another cloudburst hit the Himalayan state of Uttarakhand during the early hours of Saturday, triggering flash floods, causing landslides, and leaving several buildings and vehicles buried under debris.

According to reports, the extreme weather event occurred over Tharali in the Chamoli district, where the local tehsil complex, residential areas, including the official residence of the sub-divisional magistrate, and shops were heavily covered by debris, with some people feared trapped.

A number of cloudbursts have already been experienced this year across several northern states, including Uttarakhand, Himachal Pradesh, and Jammu and Kashmir, leading to the loss of lives as well as heavy damage to property and infrastructure.

What is a cloudburst?

A cloudburst is defined as very heavy, localised rainfall, measuring 100 mm per hour over a small area, generally around 30 square kilometers. It appears as if the clouds are discharging all their moisture content at once, and at times they have also been referred to as ‘rain bombs’.

Cloudbursts generally occur in the mountains, though there are instances of them occurring in other regions if similar meteorological conditions develop. The occurrence of cloudbursts during the Monsoon season is much higher than at other times of the year.

According to weather experts, the cause of a cloudburst lies in the atmospheric conditions developing due to prevailing air currents, the movement of clouds, and the underlying terrain. When warm, moist air from low-lying areas is pushed upward along mountain slopes through a process called ‘Orographic lifting’, the air rises rapidly to higher altitudes, having lower atmospheric pressure, it expands and cools adiabatically.

When the air reaches its dew point, water vapor condenses into droplets, forming cumulonimbus clouds. Strong updrafts within these clouds suspend water droplets and ice particles, preventing them from falling.

The clouds become heavily saturated until the updrafts weaken or the droplets become too large to hold, causing a sudden downpour. The rain is further intensified by a process called ‘Langmuir precipitation’, in which large falling raindrops collide with and absorb smaller droplets, causing them to grow in size. A cloudburst may last from a few minutes to several hours.

Can cloudbursts be predicted?

While meteorologists can forecast with a high degree of accuracy, which areas may receive light, moderate, heavy, or very heavy rainfall, the same is not the case with cloudbursts because of their local nature, short duration, and suddenness.

Data from satellites is extensively used in tracking atmospheric conditions and detecting large-scale weather systems, but the resolution of the precipitation from these satellites is lower than the area covered by a developing cloudburst. Consequently, they go unnoticed. Weather forecast models also face a similar challenge in simulating the clouds at a high resolution.

Experts say that skillful forecasting of rainfall in mountainous areas is challenging due to uncertainties in the interface between moisture convergence and the terrain, cloud microphysics, and the heating-cooling mechanisms at different atmospheric levels.

Moreover, inadequate infrastructure like early warning sensors and Doppler radars is also an issue. Meteorologists say that to forecast the weather of a particular area, inputs are required from a vast region covering several hundred kilometers.

New technologies for advanced weather monitoring, like artificial intelligence embedded tools and machine learning, are being developed to provide short-term warnings and improve the overall prediction accuracy. While prediction of a specific cloudburst event may not be feasible in the near future, determining extreme rainfall events that could result in a cloudburst-like situation is possible a few hours in advance.

According to media reports, in October 2010, a cloudburst over Pashan in Pune may have been the world's first predicted cloudburst. That day, since 2:30 PM, a weather scientist, Kiran Kumar Johare, had sent out several messages to the authorities warning of an impending cloudburst over the area. On that day, the city recorded 181.3 mm of rain in less than 90 minutes in the evening. He had claimed that his predictions were based on actual observations of storms in Kharagpur and Guwahati.

Vulnerability in the Himalayas

The frequency and intensity of extreme weather events like cloudbursts in the Himalayas are linked to climate change and global warming. Human activities have amplified disaster risks in the Himalayas, which also include large areas in neighboring Pakistan that have witnessed death and destruction.

Unregulated development, construction on unstable slopes and flood-prone riverbanks, settlements without geological assessment, and infrastructure projects destabilize the terrain and are also an impediment to the natural flow of water resulting from heavy rain.

The government has recognised that extreme weather events, such as cloudbursts, floods, heatwaves, and cyclones, are becoming more frequent and severe due to climate change. It has said so in replies to questions raised by Members of Parliament.

The Economic Survey of 2025 also highlighted that frequent extreme weather events have contributed to issues like food inflation, particularly due to crop damage in major horticultural states.

According to the Ministry of Earth Sciences, there has been a long-term increase in cloudburst events, with an estimated rise of five cloudbursts per decade in the Himalayan region and the west coast since 1969 due to microclimatic changes driven by factors like deforestation and land-use changes.

Some studies which have been conducted with the limited data available indicate that the southern rim of the Indian Himalayas, especially over Uttarakhand, Himachal Pradesh, and hilly areas of northeast India are prone to cloudbursts. The west coast of India covering the windward side of Western Ghats from Goa to Gujarat, and some regions at elevations of 1,000 meters to 2,500 meters have become more vulnerable.

One such statement in Parliament states that the ministry has undertaken various initiatives to strengthen the monitoring mechanisms for the timely detection and accurate forecast of cloudbursts.

Currently, the India Meteorological Department (IMD) uses radar and automatic rain gauges for monitoring these events. These datasets will be assimilated into the IMD’s High-Resolution Rapid Refresh Modeling System and Electric Weather Research and Forecasting models to better capture and forecast cloudbursts, the statement added.