MEV 012: Unit 15 - Hydrological Hazards

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 UNIT 15: HYDROLOGICAL HAZARDS

15.0 Introduction

Hydrological hazards are natural phenomena related to the movement, distribution, and quality of water on Earth. These include events like cyclones, hurricanes, typhoons, tsunamis, floods, and droughts. They are some of the most destructive hazards, affecting millions of people every year and leading to loss of life, property damage, and environmental degradation. Climate change, unplanned urbanization, and deforestation have increased the frequency and intensity of these hazards.

15.1 Objectives

By the end of this unit, you will be able to:

  • Define and distinguish various types of hydrological hazards
  • Understand their causes and contributing factors
  • Identify geographical areas most at risk
  • Examine the impacts on society and ecosystems
  • Review case studies to understand the real-world consequences
  • Appreciate the importance of early warning systems and mitigation strategies

15.2 Types and Causes of Hydrological Hazards

Hydrological hazards are caused by the dynamic interaction of atmospheric, oceanic, and terrestrial systems. Major types include:

15.2.1 Cyclones

  • Definition: Large scale air masses rotating around a strong center of low atmospheric pressure in tropical or subtropical regions.
  • Cause: Warm ocean waters (≥ 26.5°C), Coriolis effect, atmospheric instability, and low vertical wind shear.

15.2.2 Hurricanes

  • Definition: Term used for tropical cyclones in the Atlantic Ocean and Northeast Pacific.
  • Cause: Similar to cyclones, intensified by warm sea surface temperatures and conducive upper-atmosphere conditions.

15.2.3 Typhoons

  • Definition: Tropical cyclones occurring in the Northwest Pacific Ocean, especially affecting Southeast Asia.
  • Cause: Identical to cyclones and hurricanes, but the name differs by region.

15.2.4 Tsunamis

  • Definition: Series of ocean waves with extremely long wavelengths caused by underwater disturbances like earthquakes, volcanic eruptions, or landslides.
  • Cause: Sudden displacement of a large volume of water due to tectonic activity.

15.2.5 Floods and Droughts

  • Floods: Overflow of water onto normally dry land due to excessive rainfall, river overflow, dam break, or storm surge.
  • Droughts: Prolonged periods of below-average rainfall, leading to water scarcity.
  • Causes:
    • Floods: Intense rainfall, snowmelt, river blockages, poor drainage.
    • Droughts: Persistent high-pressure systems, deforestation, El Niño events.

15.3 Causes of Hydrological Hazards

  • Climatic Factors: Changes in precipitation patterns, sea surface temperature, wind currents.
  • Geophysical Factors: Tectonic shifts (for tsunamis), land use changes, erosion.
  • Anthropogenic Factors:
    • Deforestation
    • Poor urban drainage
    • Climate change
    • River encroachment and dam mismanagement

15.4 Geographical Distribution of Hydrological Hazards

Hazard

Major Affected Regions

Cyclones

Bay of Bengal, Arabian Sea, Indian Ocean, South Pacific

Hurricanes

Gulf of Mexico, Caribbean, Southeastern USA

Typhoons

East Asia (Japan, China, Philippines, Taiwan)

Tsunamis

Pacific Ring of Fire, Indian Ocean Rim

Floods

South Asia (India, Bangladesh), Central Europe, Sub-Saharan Africa

Droughts

Sahel region, Australia, parts of India, California

15.5 Impact on Life, Property and Environment Due to Various Hydrological Hazards

  • Loss of Human Life: Thousands die every year due to drowning, landslides, and starvation.
  • Economic Damage: Infrastructure destruction, agricultural losses, disruption of trade and services.
  • Displacement: Millions are rendered homeless due to flooding or cyclone impact.
  • Health Risks: Waterborne diseases (cholera, dysentery), vector-borne diseases (malaria, dengue).
  • Environmental Impacts:
    • Soil erosion
    • Contamination of freshwater sources
    • Destruction of coastal ecosystems (mangroves, coral reefs)

15.6 Case Studies Pertaining to Hydrological Hazards

15.6.1 Cyclones – Cyclone Fani (India, 2019)

  • Category 4 storm hitting Odisha
  • Winds over 200 km/h
  • Evacuation of 1.2 million people helped limit fatalities
  • Severe damage to infrastructure and agriculture

15.6.2 Hurricanes – Hurricane Katrina (USA, 2005)

  • One of the deadliest hurricanes in US history
  • Over 1,800 deaths
  • Damage: Over $125 billion
  • Poor disaster response highlighted need for systemic reform

15.6.3 Typhoons – Typhoon Haiyan (Philippines, 2013)

  • Category 5 typhoon with wind speeds over 300 km/h
  • Over 6,000 deaths
  • Massive storm surges and flooding
  • Highlighted the vulnerability of coastal cities

15.6.4 Tsunamis – Indian Ocean Tsunami (2004)

  • Triggered by a 9.1 magnitude earthquake off Sumatra
  • Waves over 30 meters high
  • Over 230,000 deaths across 14 countries
  • Prompted global efforts to establish tsunami warning systems

15.6.5 Floods – Bihar Floods (India, 2008)

  • Kosi River changed course due to embankment failure
  • Affected 2.3 million people
  • Massive destruction of cropland and housing

15.6.6 Droughts – Cape Town Water Crisis (South Africa, 2015–2018)

  • Severe drought conditions led to “Day Zero” water restrictions
  • Climate change and poor water management were key contributors
  • Urged global cities to rethink water use and conservation

15.7 Let Us Sum Up

Hydrological hazards are among the most common and destructive natural events. From cyclones to droughts, these events have devastating effects on human settlements, economies, and ecosystems. Understanding their causes, geographic patterns, and impacts allows for better risk assessment and disaster preparedness. Real-life case studies highlight the importance of early warning systems, infrastructure planning, and sustainable resource management.

15.8 Keywords

·         Hydrological Hazard-Natural events related to water systems (e.g., cyclones, floods, droughts)

·         Cyclone-Rotating system of winds formed over warm tropical oceans

·         Hurricane-A cyclone in the Atlantic/Northeast Pacific

·         Typhoon-A cyclone in the Northwest Pacific region

·         Tsunami-Sea waves caused by underwater disturbances like earthquakes

·         Flood-Overflow of water onto normally dry land

·         Drought-Period of prolonged low rainfall leading to water scarcity

·         El Niño-Climate pattern associated with warming of the central and eastern Pacific Ocean

·         Storm Surge-Abnormal rise in sea level accompanying a cyclone

·         Water Scarcity-Insufficient water availability to meet demand

 

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