Indian Geography — Floods
1. Introduction to Floods
Context: Floods are one of the most common and devastating natural disasters in India. Understanding their distribution and causes is crucial for UPSC preparation.
- Definition: Floods occur when surface runoff exceeds the carrying capacity of river channels.
- Global Distribution: South, Southeast, and East Asian countries — particularly China, India, and Bangladesh.
- India's Flood-Prone Area: According to the Rashtriya Barh Ayog (National Flood Commission), 40 million hectares of land are flood-prone in India.
📝 UPSC Previous Year Questions:
- UPSC Prelims 2019: Which states are among the high flood-prone states of India? Answer: Assam, West Bengal, and Bihar.
- UPSC Prelims 2017: How much land area in India is flood-prone? Answer: 40 million hectares.
2. Distribution of Floods
Context: Floods are prevalent in South, Southeast, and East Asian countries, with China, India, and Bangladesh being particularly vulnerable.
- Global Distribution:
- South Asian countries
- Southeast Asian countries
- East Asian countries
- Most Affected Countries: China, India, and Bangladesh.
- India's Flood-Prone Area: 40 million hectares (as per Rashtriya Barh Ayog).
- High Flood-Prone States in India:
- Assam — Brahmaputra basin
- West Bengal — Ganga and Brahmaputra deltas
- Bihar — Kosi, Gandak, and Ganga river systems
📝 UPSC Key Points:
- Most Affected Countries: China, India, Bangladesh
- India's Flood-Prone Area: 40 million hectares
- High Flood-Prone States: Assam, West Bengal, Bihar
3. Causes of Floods
- 1. Surface runoff exceeds carrying capacity: When river channels cannot accommodate the volume of water.
- 2. Storm surge: In coastal areas, cyclones cause storm surges that lead to flooding.
- 3. High intensity rainfall: For a considerably longer time period.
- 4. Melting of ice and snow: Glacial melt increases river discharge.
- 5. Reduction in infiltration rate: Deforestation, urbanization, and soil compaction reduce water absorption.
- 6. Presence of eroded material: Silt and debris in water reduce the carrying capacity of rivers.
📝 UPSC Key Points — Causes of Floods:
- Primary Cause: Surface runoff exceeding river carrying capacity
- Coastal Cause: Storm surge
- Climatic Cause: High intensity rainfall for long duration
- Glacial Cause: Melting of ice and snow
- Anthropogenic Cause: Deforestation, urbanization (reduced infiltration)
4. Summary: Floods at a Glance
| Category | Details |
|---|---|
| Global Distribution | South, Southeast, East Asia |
| Most Affected Countries | China, India, Bangladesh |
| India's Flood-Prone Area | 40 million hectares |
| High Flood-Prone States | Assam, West Bengal, Bihar |
| Primary Cause | Surface runoff exceeds carrying capacity |
| Coastal Cause | Storm surge |
| Anthropogenic Causes | Deforestation, urbanization, reduced infiltration |
Key Takeaways for UPSC
- Flood-Prone Area in India: 40 million hectares — UPSC 2017
- High Flood-Prone States: Assam, West Bengal, Bihar — UPSC 2019
- Most Affected Countries: China, India, Bangladesh
- Primary Cause: Surface runoff exceeding river carrying capacity
- Coastal Cause: Storm surge
- Other Causes: High intensity rainfall, glacial melt, reduced infiltration, eroded material
High-Yield Interactive UPSC Quiz (Floods)
Q1. According to the Rashtriya Barh Ayog, how many hectares of land in India are flood-prone?
Correct Answer: C. According to the Rashtriya Barh Ayog (National Flood Commission), 40 million hectares of land are flood-prone in India. (UPSC 2017)
Q2. Which of the following are among the high flood-prone states of India?
Correct Answer: C. Assam, West Bengal, and Bihar are among the high flood-prone states of India. These states are located in the Ganga-Brahmaputra basin. (UPSC 2019)
Q3. Which countries are most affected by floods?
Correct Answer: D. China, India, and Bangladesh are among the most flood-affected countries in the world, due to their large river systems and monsoon climate.
Q4. What is the primary cause of floods?
Correct Answer: B. Floods occur when surface runoff exceeds the carrying capacity of river channels, causing water to overflow onto adjacent land.
Q5. Which of the following is a cause of floods in coastal areas?
Correct Answer: B. Storm surges in coastal areas, often caused by cyclones, lead to flooding. This is a major cause of floods in coastal regions.
Q6. Which river basin in India is most prone to flooding?
Correct Answer: C. The Brahmaputra basin, especially in Assam, is one of the most flood-prone regions in India due to high rainfall and glacial melt.
Q7. Which of the following factors reduces infiltration rate and contributes to flooding?
Correct Answer: B. Urbanization reduces infiltration rate as concrete and asphalt surfaces prevent water from seeping into the ground, increasing surface runoff and flood risk.
Q8. High intensity rainfall for a considerably longer time period leads to:
Correct Answer: B. High intensity rainfall for a considerably longer time period is a major cause of floods, as it increases surface runoff beyond the carrying capacity of rivers.
Q9. The presence of eroded material in water contributes to flooding because:
Correct Answer: B. The presence of eroded material (silt and debris) in water reduces the carrying capacity of river channels, making them more prone to overflowing.
Q10. Floods are most common in which regions of the world?
Correct Answer: C. Floods are most common in South, Southeast, and East Asian countries, particularly China, India, and Bangladesh, due to the monsoon climate and large river systems.