Hydrometeorological Hazards: From Cyclones to Droughts

Natural disasters shaped by weather and water systems pose some of the greatest threats to communities worldwide. Hydrometeorological hazards encompass a range of destructive phenomena from violent tropical cyclones to prolonged droughts that can devastate entire regions. Understanding how these hazards form, spread, and impact vulnerable areas is critical for disaster preparedness and mitigation efforts.

Tropical cyclones: Nature’s most powerful storms
Devastating impact on coastal communities
Heavy rainfall and cloudbursts: Sudden atmospheric violence
Recent cloudburst events in Tamil Nadu
Floods: Overwhelming India’s river basins
Spatial patterns of flooding
Droughts: Silent devastation in rain-scarce regions
Causes and impacts of prolonged drought

Tropical cyclones: Nature’s most powerful storms

Tropical cyclones form over warm ocean waters when sea surface temperatures exceed 27°C, drawing energy from the heat and moisture of the ocean. The Bay of Bengal is notorious for generating devastating tropical cyclones, with exceptionally high sea surface temperatures providing the main energy source for these storms. However, what makes Bay of Bengal cyclones particularly difficult to predict is the contrasting influence of the Tropical Easterly Jet, which creates hostile vertical wind shear that normally inhibits cyclone formation.

The Coriolis Effect plays a crucial role in cyclone development by causing the rotation of these massive storm systems. In the Northern Hemisphere, cyclones rotate counterclockwise, while in the Southern Hemisphere they spin clockwise. This rotation is essential for the development of the characteristic spiral structure and eye of the storm.

India’s subcontinent is one of the worst affected regions globally, with approximately 10 percent of the world’s tropical cyclones occurring in the North Indian Ocean basin. The Bay of Bengal and Arabian Sea generate cyclones at a ratio of approximately 4:1, with the Bay of Bengal being far more active due to warmer sea surface temperatures and higher atmospheric moisture.

Devastating impact on coastal communities

Historical cyclones have caused immense destruction along India’s eastern coast. The 1999 Odisha Super Cyclone killed around 10,000 people, while the 1970 Bhola cyclone that struck Bangladesh resulted in an estimated 300,000 to 500,000 deaths. More recently, Super Cyclone Amphan in May 2020 became the first pre-monsoon super cyclonic storm in the Bay of Bengal since 1991, forming over exceptionally warm sea surface temperatures of 32-34°C and rapidly intensifying with sustained winds reaching 240 km/h.

Storm surges accompanying these cyclones often cause the most severe damage. Storm surges are defined as the rise in sea level above the normally predicted astronomical tide, and can inundate low-lying coastal areas, causing heavy floods, eroding beaches and embankments, destroying vegetation, and reducing soil fertility. Research indicates that although the number of tropical cyclones is anticipated to decrease in the future due to a warming climate, more intense cyclones are expected to become prevalent in the northern Bay of Bengal during the post-monsoon season.

Heavy rainfall and cloudbursts: Sudden atmospheric violence

Heavy rainfall in India primarily results from orographic lifting and monsoon dynamics. When moist air masses encounter mountain barriers like the Western Ghats or Himalayas, they are forced upward, cooling and condensing to produce intense precipitation. The southwest monsoon, arriving between June and September, accounts for over 70 percent of India’s annual rainfall.

Cloudbursts represent an extreme form of precipitation event. A cloudburst is often defined as more than 100 mm per hour rainfall within a limited geographical area of a few square kilometers. These sudden, intense downpours occur when atmospheric conditions align perfectly, often through orographic lift or when warm air parcels mix rapidly with cooler air, resulting in sudden condensation.

Recent cloudburst events in Tamil Nadu

Tamil Nadu has witnessed several severe rainfall events in recent years. In December 2023, Kayalpattinam recorded unprecedented rainfall during the northeast monsoon, becoming the only dry plain of the east coast to receive such intense rainfall. The event was particularly noteworthy as most instances of extreme rainfall exceeding 100 cm in 24 hours typically occur in hilly areas or regions close to the Western Ghats during the southwest monsoon.

More recently, in August 2025, Chennai experienced a severe cloudburst with Manali recording an unprecedented 27 cm of rainfall within a 24-hour period, with a staggering 12 cm falling in just one hour. This extreme weather event caused significant waterlogging and infrastructure strain, particularly in low-lying regions. The cloudburst over Chennai’s Manali area caused intense rainfall and waterlogging, forcing flight diversions to Bengaluru.

Mountainous regions are more prone to cloudbursts due to orography, with hilly areas in Himachal Pradesh, Uttarakhand, and the coastal areas of several states experiencing these phenomena more frequently. The difficulty in predicting cloudbursts stems from their very small scale in both space and time, making them challenging for current forecasting models.

Floods: Overwhelming India’s river basins

Flooding in India occurs due to multiple factors including excessive rainfall, storm surges, poor drainage systems, and the release of water from dams. The low-lying river basins in India are highly susceptible to flash floods, with intense rainfall associated with tropical cyclones and the summer monsoon being primary drivers.

Nearly 75% of total Indian rainfall occurs during the brief monsoon season from June to September. As a result, rivers witness heavy discharge during these months, leading to widespread floods in states like Uttar Pradesh, Bihar, West Bengal, and Assam. The most flood-prone areas in India are the Brahmaputra and Ganga River basins in the Indo-Gangetic-Brahmaputra plains, which carry 60 percent of the nation’s total river flow.

Spatial patterns of flooding

Research reveals that peninsular river basins face a higher probability of widespread flooding compared to the Ganga and Brahmaputra. The Narmada basin has the highest probability at 59 percent, followed by Mahanadi at 50 percent, Godavari at 42 percent, and Krishna at 38 percent. In contrast, the transboundary Ganga and Brahmaputra basins have probabilities of 21 percent and 18 percent respectively.

Flash flood hotspots are mainly centered in the Himalayas, West Coast, and Central India, with geomorphological factors driving flash floods in the Himalayas while hydrological factors such as flashiness dominate in the West Coast and Central India. Most flash floods occur between June and September during the summer monsoon, with approximately three-fourths triggered by the combination of extreme precipitation and wet antecedent conditions.

Droughts: Silent devastation in rain-scarce regions

Droughts represent a more insidious threat, developing slowly over months or years. The Bundelkhand region spreading across Uttar Pradesh and Madhya Pradesh is one of the most drought-prone regions, with arid soils receiving less than 750 mm of rainfall annually. This places enormous pressure on water resources, making farmers highly vulnerable to changing rainfall patterns.

The Marathwada region in Maharashtra has been classified as severely drought-prone, with hot and dry weather for most parts of the year and average annual rainfall around 750-1000 mm. Even small changes in monsoon patterns can lead to water crises in this region. The 2015 drought had a significant impact on the Marathwada area, which continues to experience exceptional water shortages.

Causes and impacts of prolonged drought

Droughts in these regions stem primarily from erratic monsoons and inadequate water management. Central and Western India experience more frequent and severe droughts due to lower and more erratic rainfall patterns compared to other parts of the country. The southwest monsoon, which accounts for over 70 percent of annual rainfall in these states, has shown a declining trend over recent decades.

The consequences extend far beyond agriculture. Water scarcity affects drinking water supplies, leads to crop failures, reduces agricultural productivity by 20-40 percent in rain-fed areas, and forces migration from rural communities. The Bundelkhand region has witnessed farmer suicides and hunger, with marginalized communities particularly vulnerable to these recurring drought conditions.

What do you think? How can communities in drought-prone regions like Bundelkhand and Marathwada build greater resilience against future water scarcity? What role should traditional water harvesting systems play alongside modern drought mitigation strategies?

References

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Table of Contents

Tropical cyclones: Nature’s most powerful storms 🔗

Devastating impact on coastal communities 🔗

Heavy rainfall and cloudbursts: Sudden atmospheric violence 🔗

Recent cloudburst events in Tamil Nadu 🔗

Floods: Overwhelming India’s river basins 🔗

Spatial patterns of flooding 🔗

Droughts: Silent devastation in rain-scarce regions 🔗

Causes and impacts of prolonged drought 🔗