Copyright infringement not intended

Source: The guardian

Context

A committee has been formed to look into the reasons for the Dharali tragedy in Uttarakhand, which occurred on August 5, 2025. The team, which includes geologists, will present a report within a week. Rescue activities are hampered by deep debris and damaged roadways, and the death toll remains undetermined, with only one confirmed fatality.

What is Cloudburst?

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Source: Sciencedirect

Definition

• A cloudburst is a sudden and extreme precipitation event producing >10 cm rainfall in less than an hour over a small area (~10 km²).

Characteristics:

• Often accompanied by hail, thunder, and sometimes lightning.
  
  
• Common in mountainous terrains (especially Himalayas, Western Ghats) due to orographic influence.
  
  
• Short duration but high intensity makes them difficult to predict and monitor.
  
  
• Potential to cause flash floods, debris flows, and landslides in downstream areas.
  
  
• IMD Classification – Rainfall intensity >100 mm/hour over a small area is considered a cloudburst.
  

Causes

• Orographic Lifting
  
  
• Moist monsoon air rises over mountains → adiabatic cooling → condensation → rainfall.
  
  
• Strong updrafts suspend large raindrops; sudden collapse of updrafts leads to intense downpour.
  
  
• More frequent when Western Disturbances interact with monsoon winds.
  
  
• Monsoon Dynamics
  
  
• Bay of Bengal & Arabian Sea monsoon clouds move inland and are blocked by Himalayas.
  
  
• Release rainfall up to 75 mm/hour or more.
  
  
• Enhanced during break monsoon phases or when low-pressure systems track northwards.
  
  
• Other Contributing Factors
  
  
• Localized convective activity due to high surface heating.
  
  
• Influence of Western Disturbances in pre- and post-monsoon seasons.
  
  
• Climate change increasing moisture-holding capacity of air, making such events more intense.
  

Examples

• Dharali (2025) – Cloudburst, followed by flash floods and landslides
• Himachal Pradesh (July 2024) – Cloudburst in Kullu-Manali; flash floods damaged roads, homes.
  
  
• Uttarakhand (August 2021) – Chamoli and Rudraprayag districts saw loss of lives, road blockages.
  
  
• Leh (2010) – Cloudburst killed >200 people; caused mudslides and destruction in a high-altitude desert region.
  

NDMA Guidelines

• Establish early warning systems and real-time weather monitoring.
  
  
• Develop community awareness programs on cloudburst risks and evacuation protocols.
  
  
• Implement watershed management and rainwater harvesting to reduce runoff.
  
  
• Design and maintain drainage systems and slope stabilization structures.
  

What is a Landslide?

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Source: Researchgate

Definition

• Downslope movement of rock, soil, debris, or earth materials under the influence of gravity.
  
  
• Classified as a mass wasting process.
  
  
• Can occur rapidly or gradually, depending on trigger and slope material.
  

Types

• Rockfall – Free fall of rock from steep slopes/cliffs.
  
  
• Debris Flow – Rapid movement of water-saturated debris.
  
  
• Slump – Rotational movement of soil/rock along a curved surface.
  
  
• Creep – Extremely slow downslope movement over years.
  
  
• Topples & Translational Slides – Blocks tilting or sliding along planar surfaces.
  
  

Causes

• Natural Factors
  
  
• Heavy/prolonged rainfall → pore water pressure increase.
  
  
• Earthquakes shaking unstable slopes.
  
  
• Water seepage reducing cohesion.
  
  
• Human-Induced Factors
  
  
• Deforestation removing root binding.
  
  
• Road building & hill cutting without slope stabilization.
  
  
• Quarrying & unplanned urbanisation.
  
  
• Geological Factors
  
  
• Weak rock formations, weathered soils.
  
  
• Steep terrain with high relief.
  
  

Landslide-Prone Areas in India

• North East Himalaya – Sikkim, Arunachal Pradesh, Nagaland, Meghalaya.
  
  
• North West Himalaya – Himachal Pradesh, Uttarakhand, J&K.
  
  
• Western Ghats – Kerala, Karnataka, Maharashtra.
  
  
• Konkan Hills & Eastern Ghats.
  
  
• Coverage – ~0.42 million sq. km (12.6% of India).
  

Examples

• Uttarkashi, Himachal Pradesh (2025) – Triggered by flashfloods, led to destruction of the area.
• Wayanad, Kerala (2024) – Triggered by monsoon; destruction of villages.
  
  
• Kedarnath, Uttarakhand (2013) – Landslide + flash flood killed over 5,700.
  
  
• Chamoli, Uttarakhand (2021) – Glacier burst induced landslide blocked river, caused flooding.
  

NDMA Guidelines:

• Conduct hazard zonation mapping to identify vulnerable areas.
  
  
• Enforce land-use regulations restricting construction on unstable slopes.
  
  
• Promote afforestation and bioengineering techniques for slope stabilization.
  
  
• Prepare community-based landslide risk management plans.
  
  
• Ensure early warning systems using rainfall thresholds and ground movement sensors.

What is a flash flood?

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Source: Britannica

Definition

• Rapid onset flooding within 6 hours of the causative event (usually intense rainfall) is called a flash flood.
  
• Highly localized but can be extremely destructive.
  
  
• Short duration but very high water velocity makes them hazardous.
  

Causes

• Primary
  
  
• Intense rainfall exceeding soil infiltration and drainage capacity.
  
  
• Other Triggers
  
  
• Sudden snowmelt from heatwaves.
  
  
• Dam or levee breaches.
  
  
• Ice/debris jams blocking rivers.
  
  
• Glacial Lake Outburst Floods (GLOFs).
  
• Urban Factors
  
  
• Impervious concrete/asphalt surfaces increase surface runoff.
  
  
• Poor drainage systems exacerbate waterlogging.
  

Examples

• Uttarkashi (2025) – Cloudburst followed by flashfloods damaged and lost lives
• Himachal Pradesh (2023) – Cloudburst-induced flash floods damaged infrastructure.
  
  
• Uttarakhand (2013) – Extreme rainfall + GLOF led to Kedarnath tragedy.
  
  
• Mumbai (2005) – 944 mm rain in 24 hours caused citywide flooding and over 500 deaths.

NDMA Guidelines

• Establish flood forecasting and warning systems linked with meteorological data.
  
  
• Develop floodplain zoning and avoid settlement in high-risk areas.
  
  
• Improve urban drainage infrastructure to manage runoff effectively.
  
  
• Conduct mock drills and public awareness campaigns on flash flood response.
  
  
• Integrate post-disaster recovery and rehabilitation plans for affected communities.

Consequences of Cloudburst, Landslide, and Flash Floods

• Loss of Life and Injuries
  Sudden, intense rainfall from cloudbursts can cause rapid flooding, leading to drowning and injuries. Landslides can bury homes, roads, and people under debris, causing fatalities and serious injuries. Flash floods sweep away anything in their path, often trapping or harming people.
• Damage to Infrastructure
  Roads, bridges, railways, and communication lines get washed away or blocked, disrupting transport and connectivity. Power lines and water supply systems may be damaged, causing outages and shortages.
• Destruction of Property and Homes
  Homes and buildings may collapse or get severely damaged by landslides or flooding. Agricultural land can be submerged or eroded, destroying crops and affecting livelihoods.
• Environmental Impact
  Soil erosion and deforestation increase due to landslides and floods, leading to long-term land degradation. Water bodies may get polluted with debris and chemicals, harming aquatic life.
• Economic Losses
  Local economies suffer due to damage to businesses, agriculture, and infrastructure. Recovery and rebuilding costs strain government and community resources.
• Displacement and Social Disruption
  Communities are often forced to evacuate or relocate, losing their homes and possessions. Psychological trauma and social unrest may follow due to loss and uncertainty.

Impact of Climate Change on Cloudburst, Landslides, and Flash Floods

• Climate change causes warmer air temperatures, allowing the atmosphere to hold more moisture, leading to more frequent and intense cloudbursts with sudden heavy rainfall.
• Intense and rapid rainfall often overwhelms drainage systems, increasing the risk and frequency of flash floods that can occur with little warning.
• Prolonged or heavy rains saturate the soil, weakening its structure and making slopes more vulnerable to landslides, especially in mountainous regions.
• Disruption of traditional weather patterns by climate change results in unpredictable and erratic rainfall, making it harder to anticipate and prepare for extreme events.
• Rising temperatures cause accelerated glacial melt and reduce snowpack in mountainous areas, leading to sudden surges in river flows that can trigger flash floods and landslides.
• Reduced vegetation cover due to changing climate conditions decreases soil stability, making ecosystems and communities more vulnerable to the damaging effects of landslides and floods.

Source: Downtoearth