Flash Floods

Table of Contents

Context: In the Union Territory of Ladakh, a cloudburst caused flash floods that brought debris into residential areas, disrupting livelihoods.

What are Flash Floods?

Flash floods are floods that occur suddenly and with little warning, usually within six hours of the onset of heavy rainfall.
They are characterized by rapid and intense inundation of water, which can cause significant damage and pose a threat to life and property.
Flash floods are often associated with cloud bursts, storms, cyclones, or other intense weather events.
Flash flooding commonly happens more where rivers are narrow and steep, so they flow more quickly.
They can also occur in urban areas located near small rivers, since hard surfaces such as roads and concrete do not allow the water to absorb into the ground.

Causes of Flash Floods

Heavy Rainfall: When the rate of precipitation exceeds the soil’s ability to absorb water, the excess water quickly runs off, leading to flooding.
Saturated Soil: If the soil is already saturated due to previous rainfall or a prolonged wet period, it cannot absorb additional water, leading to an increased risk of flash flooding.
Drought Conditions: Surprisingly, flash floods can occur after a period of drought. Dry and hardened soil cannot readily absorb sudden heavy rainfall, resulting in rapid runoff and flash floods.
Cloudbursts and Thunderstorms: Cloudbursts are sudden, intense rainfall events localized in a specific area. Thunderstorms can also produce heavy rainfall over a short period, contributing to flash floods.
Melting Snow or Glaciers: Rapid melting of snow or glaciers, especially in mountainous regions, can contribute to flash floods downstream.
Breaches or Dam Failures: Sudden release of water from upstream reservoirs, breaches in landslide dams, or embankment failures can lead to flash floods.

Flash Floods in India

India is the worst flood-affected country in the world after Bangladesh and accounts for one-fifth of the global death count due to floods.

In India, flash floods are often associated with cloudbursts.
The young Himalayan mountain range is highly prone to flash floods owing to overflowing glacial lakes formed due to the melting of glaciers.
Depression and cyclonic storms in the coastal areas of Orissa, West Bengal, Andhra Pradesh cause flash floods.
States of Arunachal Pradesh, Assam, Orissa, Himachal Pradesh, Uttarakhand, the Western Ghats in Maharashtra and Kerala are more vulnerable to flash floods caused by cloud bursts.
Floods in Assam, Bihar, Uttar Pradesh, Orissa and Andhra Pradesh are generally caused by breaches in embankments.

Uttarakhand Floods, 2013

The state of Uttarakhand and the adjoining areas received heavy rainfall in June, 2013, which was about 375% more than the benchmark rainfall in a normal monsoon. The major reason for the flash flood was extreme rainfall, melting of Chorabari Glacier and eruption of the Mandakini River.

Reasons for Flash Floods in India:

As per data from the National Disaster Management Authority, nearly 75% of the total Indian rainfall is concentrated over a short monsoon season of four months (June to September). As a result, the rivers witness a heavy discharge during these months.
About 40 million hectares of land in the country are liable to floods according to the National Flood Commission.
An average of 18.6 million hectares of land are affected annually by floods.

Impacts of Flash Floods

Loss of Life and Injury: They can lead to drowning, injuries, and even loss of life, especially in areas where warning systems and preparedness measures are inadequate.
Property Damage: Floodwaters can damage or destroy homes, buildings, and infrastructure such as roads, bridges, and utilities.
Displacement and Homelessness: Flash floods can force people to evacuate their homes, leaving them temporarily or even permanently displaced.
Crop and Livestock Losses: Floodwaters can destroy crops and wash away livestock, leading to significant losses for farmers and agricultural communities.
Spread of Waterborne Diseases: Stagnant water after flash floods can become breeding grounds for disease-carrying mosquitoes and other vectors, leading to an increased risk of waterborne illnesses.
Erosion and Sedimentation: Flash floods can cause erosion of soil and sediment deposition in water bodies, affecting aquatic ecosystems and contributing to siltation in rivers and reservoirs.

Government Initiatives

Flash Flood Guidance Services: The India Meteorological Department (IMD) developed a reliable system to deliver the required products in real-time to support the creation of warnings for flash floods about 6–12 hours in advance at the watershed level for the flash flood-prone South Asian countries, namely India, Nepal, Bhutan, Bangladesh, and Sri Lanka.
South Asian Flash Flood Guidance System (FFGS):
- The South Asian FFGS was introduced by the India Meteorological Department (IMD).
- It is intended to support emergency response teams.
- Aids in the prompt creation of evacuation preparations by governments before flooding actually occurs.

Dealing with Flash Floods

The need to have strict implementation of the Flood Plain Zoning Act which can regulate the constructions within the flood plain of a river.

Landslide risk zonation mapping be completed on priority. Development and enforcement of guidelines, regulations and codes for landslides is critical.
Construction of flood protection embankments in the flood-prone areas, construction of dams, afforestation should be done.
Effective stabilization of slopes in weak zones be undertaken using scientific techniques available at national/international levels.
Blasting for developmental activities be avoided as it may destabilise the weak rocks in mountainous regions.
The existing emergency communication system be reviewed regularly to ensure last mile connectivity during disasters
Investments in infrastructure development related to weather, glacial lakes, river flow monitoring, etc. are fundamental for improving the accuracy of risk mapping.
Tourism related development should not be allowed along the river banks.
An effective pilgrim control and regulatory body should be constituted for control and management of pilgrims/tourists.