There are years when nothing happens, and then there are days when years happen. The cloudbursts in Dehradun in Uttarakhand and Mandi in Himachal Pradesh in September 2025 close on the heels of similar events in these states earlier in July and August elucidate and echo this sentiment. Similarly, the city of Hyderabad witnessed cloudbursts in August and September this year. A common question people ask, Is there an increase in such events in recent years? The answer is Yes.
Data gathered from newspaper reports and some rainfall measurements show that 13 major cloudbursts in the Indian Himalayan region occurred between 1970 and 2000. In comparison, 16 devastating cloudbursts have already occurred in the last two decades in the Himalaya, and central and south India. These are Leh, Ladakh (2010), Kedarnath, Uttarakhand, (2013), two in Lahaul-Spiti area (2021) and two in Mandi area (2024) in Himachal Pradesh, Lachen Valley, Sikkim (2023), four in Uttarakhand (2025), Mumbai (2005), three in Hyderabad (2017 and 2025) and Wayanad, Kerala (2024). In addition, there were several episodes of heavy rains leading to landslides in hilly regions, flooding, and waterlogging in major cities in the country. But these events were not cloudbursts by definition.
The India Meteorological Department (IMD) defined an episode of sudden and localized downpour of more than 100 mm or 4 inches of rain over a small geographical area, typically 20-30 square km, as a cloudburst. The most important ingredient for cloudbursts or, in general, monsoonal rains to occur is the tropical moisture. The moisture in the atmosphere is influenced by the uneven heating of landmasses and oceans in the tropical regions defined between 23.5° N and 23.5° S latitudes, the Tropic of Cancer and Tropic of Capricorn, respectively. This happens due to the sun’s direct rays year-round, resulting in a concentrated and consistent amount of solar energy, unlike in higher latitudes, where the sun’s rays fall at a more oblique angle. This differential heating creates temperature and pressure gradients (any matter flows from high to low) that drive wind and create global weather patterns by the influx of moist air from the ocean that fuels cloud formation and rainfall.
That is why most of the cyclonic storms originate in tropical regions and then move towards subtropics affecting countries in Asia-oceanic regions from Australia to Singapore, Indonesia, Malaysia, Thailand, Philippines, Vietnam to India, year-round rainfall in most of mid-African continent and parts of south and central American continent in Brazil and Mexico to subtropics like Japan, eastern China, Taiwan, Himalaya, Gulf of Mexico and parts of eastern America till New York city.
In the Indian context, regions below the Narmada river, say 240N, where the Tropic of Cancer passes, come under the tropical region, whereas north of it, till Jammu and Kashmir, say 380N, is sub-tropical. In this belt, the winds blow from west to east and are called westerlies that flow towards higher latitudes or poles due to the development of high pressures that originate around 300N latitude. In India, this passes through Dehradun in Uttarakhand and Chandigarh. While westerlies are the broader, prevailing winds at the Earth’s surface blowing from west to east in the mid-latitudes, i.e., 30 to 60 degrees in the northern and southern hemispheres, there are narrow, fast-flowing bands of wind in the upper atmosphere around 10 km, or 32000 feet height, called jet streams. You may have noticed that several of the commercial flights take advantage of these jet streams and mostly fly within this band of 32000 to 36000 feet to save time and fuel. These jet streams primarily influence weather by transporting weather systems from the equatorial region to the poles and vice versa.
With this background information, let us understand Indian cloudbursts, which are a common feature during the onset of monsoon in north India, especially in the regions on the southern Himalayan slopes in the foothills. The monsoon onset time differs in south and north India by about a month, after setting in June in the south. So, when the sea branches of hot air masses from the Bay of Bengal and the Arabian Sea reach the Indian mass, there are already westerly jet streams present over the Himalaya that were formed during the winter months. These jet streams, which are at an average altitude of 10 km, block the rise of the hot air mass over the Indian landmass. By the end of May, warm maritime airmass developed due to constant heating of surface water of both the Bay of Bengal and Arabian Sea accumulate substantially over Indian region and start pushing out westerly jet streams out of Himalaya, causing sudden vacuum (vacuum in literary sense only) spaces to be filled with the rising warm air, resulting in very rapid condensation and precipitation. In the Himalaya, the effect becomes more pronounced because of the additional presence of Orographic lift.
Orographic uplift is a process where moving air is forced to rise over a geographical barrier, like a mountain, as it cannot pass through it. This upward motion causes the air to cool adiabatically, leading to increased relative humidity, cloud formation, and often, precipitation on the windward side. This creates a distinct weather pattern, with a wet, vegetated windward side and a dry, desert-like “rain shadow” on the leeward (downwind) side. That is why you see deserts at high altitudes in Leh and beyond. The Himachal Pradesh and Uttarakhand states are more prone to cloudbursts as both the Bay of Bengal and Arabian Sea branch warm air masses meet in this part of the Himalaya, though there are different reasons in other parts.
Cloudburst can also occur in plain coastal cities like Mumbai or Chennai or interior parts like Hyderabad or Bengaluru due to strong monsoon winds and surges along the coast, bringing large amounts of moisture from the Arabian Sea or the Bay of Bengal. When intense monsoon winds occur, especially in coastal areas, they can push warm, moist air from the sea to inland. This atmospheric condition allows for a rapid buildup of water vapor in the atmosphere. The warm, moist air then undergoes rapid condensation, leading to the formation of deep clouds. The accumulated moisture is released in a sudden and intense burst of rain, which can last for a short period, sometimes with hail and thunder.
Normally, hail storm cloud bursts happen as the updraft in the atmosphere keeps pushing water droplets above the freezing level and turn into ice to fall as hail when it becomes too heavy to sustain the updraft. But in tropical storms, the freezing levels are very high, and even the strong updraft of the storms cannot push the water droplet above the freezing level. So instead of hail growing in size, liquid water droplets start growing in size. And if the thunderstorm suddenly weakens or the weight of all that water combines with gravity, finally overpowers the force of the updraft, the whole mass of water, along with hail, will start falling as a hail cloudburst.
As we keep arguing about climate change as the culprit for our disasters, Nature keeps acting. Let us reverse the role and start acting to be friendly to nature and take whatever is sustainable.
