MEV 002: Block-1 (Unit 04) – Weather related coastal hazards

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 UNIT 4: WEATHER-RELATED / COASTAL HAZARDS

4.0 Introduction

Weather-related and coastal hazards significantly impact human life, infrastructure, ecosystems, and economies. These hazards, driven by natural atmospheric and oceanic phenomena, include tropical cyclones, thunderstorms, tornadoes, coastal erosion, and tsunamis. With climate change influencing the frequency and intensity of these hazards, it becomes increasingly important to understand their formation, impacts, and mitigation strategies.

4.1 Objectives

After studying this unit, you will be able to:

  • Explain the formation and classification of tropical cyclones.
  • Describe the formation and characteristics of thunderstorms and tornadoes.
  • Understand the dynamics of coastal hazards including tsunamis and erosion.
  • Explore the El Niño–Southern Oscillation (ENSO) and its global implications.
  • Recognize the environmental and socio-economic impacts of these hazards.

4.2 Tropical Cyclones: Hurricanes, Typhoons, and Cyclones

Tropical cyclones are intense, rotating systems of clouds and thunderstorms that originate over warm tropical oceans and are characterized by low pressure, strong winds, and heavy rains.

4.2.1 Classification of Cyclones

Tropical cyclones are classified based on wind speed and geographic location:

  • Cyclone (Indian Ocean)
  • Hurricane (Atlantic Ocean and Eastern Pacific)
  • Typhoon (Western Pacific)

Wind-based classifications:

  • Tropical Depression: Wind speeds < 62 km/h
  • Tropical Storm: Wind speeds between 62–118 km/h
  • Severe Cyclonic Storm: Wind speeds > 119 km/h (hurricane/typhoon strength)

4.2.2 Formation of Cyclones

Cyclones form under these conditions:

  • Sea surface temperatures above 26.5°C
  • High humidity in the mid-troposphere
  • Low vertical wind shear
  • Coriolis force to initiate rotation
  • Pre-existing weather disturbance

4.3 Thunderstorms

Thunderstorms are localized weather events accompanied by lightning, thunder, rainfall, and sometimes hail.

4.3.1 Formation of Thunderstorms

  • Warm, moist air rises rapidly into the atmosphere.
  • As it cools, condensation occurs, forming cumulonimbus clouds.
  • The updraft and downdraft interactions lead to thunder and lightning.
  • Thunderstorms can evolve into supercells, which may cause severe weather.

4.4 Tornadoes

Tornadoes are violently rotating columns of air that descend from a thunderstorm to the ground, appearing funnel-shaped and capable of immense destruction.

4.4.1 Formation of Tornadoes

  • Form within severe thunderstorms (usually supercells).
  • Strong wind shear causes horizontal rotation in the atmosphere.
  • This rotation is tilted vertically by updrafts, creating a mesocyclone.
  • A condensation funnel becomes visible when the vortex reaches the ground.

4.4.2 Tornado Destruction

  • Destruction is often concentrated along a narrow path.
  • Classified using the Enhanced Fujita (EF) scale (EF0–EF5).
  • Damages homes, uproots trees, and can cause loss of life.

4.5 Introduction to Coastal Hazards

Coastal areas face hazards due to the interface between land and sea, which include:

  • Storm Surges: Elevated sea levels during cyclones or storms.
  • Coastal Erosion: Gradual loss of land due to wave action and currents.
  • Sea-level Rise: Linked to climate change and glacial melting.
  • Saltwater Intrusion: Infiltration of seawater into freshwater systems.

4.6 Introduction to Tsunamis

Tsunamis are large, powerful sea waves caused by the displacement of water due to:

  • Undersea earthquakes
  • Volcanic eruptions
  • Landslides
  • Submarine explosions

Key characteristics:

  • Speed: Can travel at 500–800 km/h in deep ocean
  • Wavelength: Long (100–200 km)
  • Not noticeable at sea but becomes destructive near coasts
  • Can cause catastrophic loss of life and property

Examples: 2004 Indian Ocean Tsunami, 2011 Japan Tsunami

4.7 El Niño / Southern Oscillation (ENSO)

ENSO is a climate pattern that involves the periodic warming (El Niño) and cooling (La Niña) of the central and eastern tropical Pacific Ocean.

  • El Niño: Warmer ocean temperatures → weaker monsoons, droughts, altered jet streams
  • La Niña: Cooler ocean temperatures → enhanced rainfall in Asia, stronger hurricanes in the Atlantic
  • Southern Oscillation: The atmospheric component, involving shifts in air pressure patterns between Tahiti and Darwin

Global impacts:

  • Changes in monsoon patterns
  • Altered agricultural productivity
  • Droughts in Australia, floods in South America

4.8 Let Us Sum Up

Weather-related and coastal hazards such as tropical cyclones, thunderstorms, tornadoes, coastal erosion, tsunamis, and climate oscillations like ENSO pose significant threats globally. Understanding their mechanisms helps in forecasting, preparedness, and mitigation, ultimately reducing their destructive impacts.

4.9 Keywords

·         Tropical Cyclone: A rotating storm system with strong winds and rain that forms over warm tropical oceans.

·         Hurricane/Typhoon: Regional terms for tropical cyclones with wind speeds over 119 km/h.

·         Storm Surge: Abnormal sea level rise caused by strong winds and low pressure during cyclones.

·         Thunderstorm: A storm with lightning, thunder, and often heavy rain or hail.

·         Tornado: A violently rotating column of air extending from a thunderstorm to the ground.

·         CoriolisForce: A force caused by Earth’s rotation that influences wind direction and storm rotation.

·         Coastal Erosion: The loss of coastal land due to wave action and sea-level rise.

·         Tsunami: A large sea wave caused by an underwater disturbance, such as an earthquake.

·         ENSO (El Niño–Southern Oscillation): A climate pattern involving periodic warming (El Niño) and cooling (La Niña) of the Pacific Ocean.

·         El Niño: A phase of ENSO characterized by warmer ocean temperatures and disrupted weather patterns.

·         La Niña: A phase of ENSO with cooler ocean temperatures, leading to different climate anomalies.

·         Sea-level Rise: An increase in the average level of the world's oceans, largely due to climate change.

 

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