By Prof AN Purohit
The majestic beauty of mountain landscapes often masks the lurking dangers posed by extreme weather events, especially during the monsoon season. Among the most feared natural hazards in mountainous regions are cloudbursts and thunderstorm events that can transform tranquil hillsides into sites of chaos within minutes. In this ongoing rainy season, such catastrophes were faced in Kullu, Mandi in Himachal Pradesh and Chamoli in Uttarakhand.
A cloudburst is intense and sudden rainfall, often delivering over 100 mm of rain in less than an hour over a small area. In the mountains, where slopes are steep and vegetation may be sparse, this deluge can lead to devastating flash floods, landslides, and widespread destruction. Entire villages are cut off or swept away before help can even arrive. Thunderstorms, which often accompany or precede cloudbursts, bring their own set of perils. Fierce winds, blinding lightning, and torrential rain pose threats to both human life and infrastructure. In high-altitude areas, the rugged terrain amplifies the risk, making rescue operations extremely challenging.
Specific Misery Factors
Mountains are known for rapidly changing and unpredictable weather patterns, including blizzards, extreme cold, and strong winds. Natural Disasters such as avalanches, debris flows, floods, landslides, and rock falls are common occurrences in mountainous areas, posing threats to life and property. Steep slopes, high altitudes, and rugged landscapes can make travel, construction, and agriculture challenging. Mountainous regions can be remote and isolated, making access to resources, services, and infrastructure difficult. Climate change is causing glaciers to melt at an accelerated rate, leading to increased risks of floods, landslides, and other natural disasters.
Cloudbursts (very heavy rain) and thunderstorms (lightning, thunder, wind) often occur simultaneously because they are both caused by similar atmospheric conditions, such as intensely unstable, moisture-laden air masses. When this air rises rapidly (due to heat, terrain, or weather systems, it forms large storm clouds capable of both heavy rain and electric discharges, especially during the monsoon or convective weather patterns. Both cloudbursts and electric discharges (lightning) are phenomena associated with cumulonimbus clouds, which are large, towering thunderclouds. The combined impact can be extremely dangerous and destructive. In mountainous areas like the Himalayas, the combo can trigger: Landslides, Glacial lake outbursts, Blockage of roads and disruption of communication lines. Leh (2010) and Kedarnath (2013) are recent examples of the miseries faced by the people.
Often, intense lightning is observed just before or during a cloudburst, which is a sign of a highly energetic cloud system capable of releasing massive rainfall suddenly. In Mountains, the topography enhances convection, warm air is forced upwards quickly, clouds get trapped in valleys and gorges, making intense localised rain more likely. Thunderstorms become stationary, increasing both lightning and rain intensity.
Electric discharge and cloudbursts are both symptoms of intense thunderstorm activity. Lightning indicates a highly charged and turbulent atmosphere, which is also capable of producing a cloudburst. Their frequent co-occurrence in mountains is due to the region’s geography and weather dynamics.
Cloudbursts are often associated with thunderstorms, which are characterised by strong updrafts and downdrafts of air, leading to the formation of towering cumulonimbus clouds. Within these clouds, water droplets, ice crystals, and hailstones collide and interact, causing a separation of electrical charges. Negative charges tend to accumulate in the lower parts of the cloud, while positive charges accumulate in the upper parts and sometimes on the ground below. This charge separation creates an electrical potential difference, and when this difference becomes large enough, it overcomes the insulating capacity of the air. A sudden discharge of electricity, known as lightning, occurs as the charges rush to equalise. Lightning can occur within the cloud, between clouds, or between a cloud and the ground (cloud-to-ground lightning). The same atmospheric instability and moisture that contribute to cloud formation and heavy rainfall (like in a cloudburst) also create the conditions for charge separation and lightning. Strong updrafts can carry water droplets and ice particles higher into the cloud, facilitating the charge separation process. The rapid condensation and precipitation associated with cloudbursts can also disrupt the charge distribution within the cloud, potentially triggering lightning.
In essence, both cloudbursts and lightning are consequences of the same powerful atmospheric processes, with the conditions that produce one often being conducive to the other. Lightning rods, lightning conductors or air terminals, are installed on buildings to protect them from lightning strikes. Lightning rods on buildings serve as a safety measure to protect structures from the destructive force of lightning strikes. They work by providing a safe, conductive path for the electrical charge to travel from the sky to the ground, bypassing the building and minimising the risk of fire or damage.
Cloudbursts followed by heavy rainfall are frequent during the rainy season in mountainous regions due to a combination of topographical, meteorological, and climatic factors. Here’s a breakdown of the reasons and possible ways to reduce or control their impact:
While establishing an alpine field centre in Tungnath in District Chamoli of Uttarakhand, we faced frequent thunderstorms in the area and nearby locations such as Madmaheswar area (about 3500 m asl) during rainy season of 1983-86. For our research needs, we installed an automatic weather recording system on a well-earthed 12 feet tower. Touchwood, no thunderstorm and cloudbursts have been recorded in the area after installing this system. The system was grounded though a copper plate by JK Rawat, a member of our team. This makes me recommend installing such systems or TV towers / communication towers at the highest point in the mountains, specially where there are human settlements in the nearby area. Such interventions might help in reducing the miseries due to combined effect of cloudbursts and thunderstorms in mountains.
(This write-up is partially based on a questions and answers session by the author on ChatGPT.)
