Causes of Flooding

Test yourself

Human Causes of Flooding

The likelihood of flooding happening can be significantly increased by the actions of humans in that drainage basin.

Removal of vegetation

Deforestation and removal of vegetation increase the risk of flooding in several ways:
- The ground cover decreases, meaning that interception from the plants and their leaves is reduced. This water will now just reach the ground.
- The removal of plants reduces infiltration. With less infiltration and interception, there is an increase in surface runoff.

Agriculture

As demand for food increases, so does demand for agricultural land. Increasingly farms are made on deforestation sites, for example in the Amazon.
Agricultural practices increase surface runoff and the amount of soil exposed - leading to soil erosion. Sediment from the erosion is transported to the river.
The river's water capacity is reduced by the sediment, increasing the likelihood that the river will burst its banks.

Urbanisation

Urbanisation leads to the removal of vegetation resulting in an increase in surface runoff.
An increase in impermeable man-made surfaces - i.e. concrete, tarmac and tiles - lead to no infiltration and so all rainfall experiences runoff.
Runoff enters the drainage system which quickly takes the water to rivers and waterways. This significantly reduces the lag time and promotes reaching a high peak discharge.

Floodplain drainage

Floodplain land is flat and fertile, making it desirable agricultural land but a target for floods.
In many countries, this land is drained to provide this. But the process of drying out the wetlands destroys habitats.
The drying out process leads to the area shrinking and lowering, which can actually increase the likelihood of the areas being subject to floods.

River management

River management (especially that of hard engineering systems) is meant to provide protection from flooding. But poor river management can have the opposite effect.
Channelisation (when the river is widened or deepened) and straightening the river (by cutting off meanders) has actually increased flood risk on the River Mississippi. The levees and man-made channels restrict the river, making it more likely to burst its banks.

Meteorological Causes of Flooding

Natural flooding is caused when a rivers discharge increases until the river bursts its banks. Flooding can be caused by an increase in rainfall or an increase in surface runoff water.

Flash flooding

Flash floods happen quickly and frequently without warning.
Low air pressure systems can create intense tropical storms and thunderstorms that produce heavy rainfall.

Prolonged and heavy rainfall

Prolonged and heavy rainfall can be caused by mid-latitude depressions (low air pressure systems that produce a lot of rain).
A depression happens when two air masses meet, one hot and one cold. The cold air pushes the hot air up, leading to its cooling, condensing and forming rain.
Heavy rains can lead to saturated soil, which stops infiltration and increases surface runoff. Water reaches the channel quicker and causes flooding.

Extreme monsoon rainfall

A monsoon is a seasonal change in the direction of the prevailing winds as the ITCZ (Inter Tropical Convergence Zone) moves northwards.
The change results in wet and dry seasons in subtropical areas that are close to oceans. Because of this, India and South East Asia are at particular risk.
The summer monsoon (April-September) leads to extreme rainfall in India and South East Asia. During July 2015, the heavy monsoon rain resulted in 103 deaths in Myanmar.

Snowmelt

When temperatures increase after winter, snow and ice in higher latitudes or altitudes will begin to melt.
Snowmelt is particularly evident in mountain environments and the increase in water results in increased surface runoff and consequential flash floods.

ENSO: La Niña

La Niña is a change in weather pattern across the South Pacific Ocean as part of the El Niño Southern Oscillation (ENSO) cycles.
La Niña events exaggerate the normal weather patterns. The La Nina years bring warm water and low air pressure to Australasia so the rainfall increases, as does the risk of flooding.

1Tectonic Processes & Hazards

1.1Tectonic Processes & Hazards

1.1.1Tectonic Plates

1.1.2Distribution of Tectonic Hazards

1.1.3Theoretical Frameworks

1.1.4Earthquakes

1.1.5Earthquake Hazards

1.1.6Volcanoes

1.1.7Tsunamis

1.1.8End of Topic Test - Tectonic Processes

1.1.9Exam-Style Question - Earthquakes

1.2Natural Disasters

1.2.1Introduction to Natural Disasters

1.2.2Impacts of Hazards

1.2.3Comparing Hazards

1.2.4Development & Governance

1.3Natural Disaster Case Studies

1.3.1Tohoku Earthquake & Tsunami

1.3.2Gorkha Earthquake

1.3.3Mount Merapi Eruption

1.4Trends & Patterns

1.4.1Disaster Trends

1.4.2Prediction

1.5Disaster Modification

1.5.1Hazard Management

1.5.2Modifications

1.5.3End of Topic Test - Natural Disasters

1.5.4Exam-Style Question - Disaster Modification

2Option 2A: Glaciated Landscapes & Change

2.1Glaciated Landscapes Over Time

2.1.1Timeline of Glacial Change

2.1.2Natural Causes

2.1.3Ice Distributions

2.2Periglacial Landscapes

2.2.1Periglacial Processes

2.2.2Periglacial Landforms

2.3Glacial Processes

2.3.1Mass Balance

2.3.2Glacial Movement

2.4Glacial Landforms

2.4.1Landscapes

2.4.2Erosional Landforms

2.4.3Erosional Landforms 2

2.4.4Erosional Landforms 3

2.4.5Depositional Landforms

2.4.6Fluvioglaciation

2.5The Future of Glaciated Landscapes

2.5.1The Value of Glaciated Landscapes

2.5.2The Value of Glaciated Landscapes 2

2.5.3Threats to Glaciated Landscapes

2.5.4Managing the Threats to Glaciated Landscapes

3Option 2B: Coastal Landscapes & Change

3.1Coastal Landscapes

3.1.1The Wider Coastal Landscape

3.1.2Geological Structure

3.1.3Lithology & Vegetation

3.2Coastal Erosion & Deposition

3.2.1Shaping Coastlines

3.2.2Coastal Formations

3.2.3Sediment Transportation

3.2.4Subaerial Processes

3.3Coastal Risks

3.3.1Sea Level Change

3.3.2Coastal Retreat

3.3.3Coastal Flooding

3.4Managing Coastlines

3.4.1Consequences of Coastal Recession

3.4.2Engineering Management Approaches

3.4.3Governance Approaches

4Globalisation

4.1Globalisation

4.1.1Intro to Globalisation

4.1.2Development of Globalisation

4.1.3Economic Policy & Globalisation

4.1.4Government Policy & Globalisation

4.1.5International Organisations & Globalisation

4.1.6Measuring Globalisation

4.1.7TNCs & Globalisation

4.1.8TNCs - Aramco & Anglo-Iranian Oil

4.2Negatives of Globalisation

4.2.1'Switched Off' Places

4.3Global Shift

4.3.1Global Shift for Developing Nations

4.3.2Global Shift for Developing Nations 2

4.3.3Global Shift for Developed Nations

4.3.4End of Topic Test - Globalisation

4.4Migration

4.4.1Megacities

4.4.2International Migration

4.4.3Country Interdependence

4.5Culture

4.5.1Global Culture

4.5.2Cultural Erosion

4.6Measuring Development

4.6.1Measuring Development

4.7Responses to Globalisation

4.7.1Tensions Caused by Globalisation

4.7.2Government Control of Globalisation

4.7.3Ethical Responses to Globalisation

4.7.4End of Topic Test - Migration, Culture, & Response

5Option 4A: Regenerating Places

6Option 4B: Diverse Places

6.1Population Structure

6.1.1The UK

6.1.2Population Characteristics

6.1.3Government & Change

6.2Past & Present Connections

6.2.1International Influence on Places

6.2.2Historic Influences on Places

6.2.3The Perception of Places

6.2.4Image & Identity

6.3Urban & Rural Spaces

6.3.1Perceptions of Urban Places

6.3.2Perceptions of Rural Places

6.3.3Evaluating Living Space

6.4Diversity

6.4.1UK Migrations

6.4.2Challenges

6.4.3Tensions & Conflict

6.4.4Wider Outcomes of Tensions

6.4.5Managing Tensions

6.5Urban & Rural Case Studies

6.5.1Stakeholders

6.6Case Study - Tower Hamlets

6.6.1Background

6.6.2Characteristics

6.6.3Issues

6.7Case Study - Sturton-le-Steeple

6.7.1Background

6.7.2Characteristics

6.7.3Issues

7The Water Cycle & Water Insecurity (A2 only)

7.1Hydrological Processes Global to Local

7.1.1Global Hydrological Cycle

7.1.2Drainage Basin Hydrological Cycle

7.1.3Water Budgets

7.1.4River Regimes

7.1.5Storm Hydrographs

7.2Influences on the Water Cycle

7.2.1Causes of Drought

7.2.2Impacts of Drought

7.2.3Causes of Flooding

7.2.4Impacts of Flooding

7.2.5Climate Change & The Water Cycle

7.2.6Impacts of Climate Change

7.2.7End of Topic Test - The Water Cycle

7.3Water Insecurity

7.3.1Water Stress

7.3.2Causes of Water Insecurity

7.3.3Water Insecurity Risk

7.3.4Conflict Over Water

7.4Water Supply Management

7.4.1Hard Engineering Schemes

7.4.2Sustainable Management

7.4.3Water Treaties & Framework

7.4.4End of Topic Test - Water Insecurity & Management

8The Carbon Cycle & Energy Security (A2 only)

8.1The Carbon Cycle

8.1.1Carbon Stores

8.1.2Carbon Stores 2

8.1.3Biological Carbon

8.1.4Atmospheric Carbon

8.1.5Burning Fossil Fuels

8.2Energy Consumption

8.2.1Consumption

8.2.2Access to Energy

8.2.3Energy Players

8.2.4Supply & Demand

8.2.5Pathways

8.2.6End of Topic Test - Carbon & Consumption

8.3Alternative Energy

8.3.1Unconventional Fuels

8.3.2Non-Fossil Fuels

8.3.3Non-Fossil Fuels 2

8.4Growing Demand for Resources

8.4.1Deforestation

8.4.2Water

8.4.3Climate Change

8.5The Future

8.5.1Future Uncertainty

8.5.2Adaptation Strategies

8.5.3Mitigation Strategies

9Superpowers (A2 only)

9.1Superpowers

9.1.1Introduction to Superpowers

9.1.2Superpowers - Economic Power & Size

9.1.3Superpowers - Political & Military Power

9.1.4Superpowers - Culture, Demography & Resources

9.1.5Geo-Strategic Location

9.2Hard & Soft Power

9.2.1Hard & Soft Power

9.2.2Emerging Powers - China Rivalry

9.2.3Emerging Powers - Chinese Sources of Power

9.2.4Emerging Powers - Brazil

9.2.5Emerging Powers - Russia

9.2.6Emerging Powers - India

9.2.7Theories of Development

9.2.8Power Case Studies: Chinese One Belt One Road

9.2.9Power Case Studies: Pakistan Nuclear Arms

9.2.10Power Case Studies: OPEC

9.3IGOs, TNCs & Alliances

9.3.1Superpowers & IGOs

9.3.2Superpowers & TNCs

9.3.3Superpowers & Global Action

9.3.4Superpowers & Alliances

9.3.5Superpowers & the Environment

9.4Changing Global Influence

9.4.1Recent Tensions between Powers

9.4.2China in Africa & Asia

9.4.3Tensions in the Middle East

9.4.4Economic Problems for Superpowers

9.4.5Future Pattern of Power

10Option 8A: Health & Human Rights (A2 only)

11Option 8B: Migration & Identity (A2 only)

11.1Globalisation & Migration

11.1.1Intro to Migration

11.1.2Trends in Migration

11.1.3Common Migration Patterns

11.1.4Causes of Migration

11.1.5Restrictions on Migration

11.2Consequences of Migration

11.2.1Intro to Culture

11.2.2Social & Demographic Tensions of Migration

11.2.3Political & Economic Tensions of Migration

11.3Nation States

11.3.1Intro to Nation States

11.3.2Borders

11.3.3Nationalism

11.4Responses to Global Migration

11.4.1Responses to Global Migration

11.4.2Global Organisations

11.4.3IGOs and World Trade

11.4.4Financial IGOs

11.4.5Environmental IGOs

11.5Sovereignty & Identity

11.5.1Sovereignty & Nationalism

11.5.2Complex Identities

11.5.3Challenges to National Identities

11.5.4Tensions within Nations

11.5.5Failed States

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