Earth: Our Home Full Geography
CHAPTER 8
Floods and Droughts
Chapter 3: Plate Tectonics
You
w ill learn« will learn«
-
to describe the natural and human causes of floods and droughts
-
to discuss the impact of floods and droughts on human lives and the environment
-
to evaluate the effectiveness of management management strategies taken to mitigate and adapt to floods and droughts
Floods and Droughts
Floods occur when land that is usually dry is submerged by large amounts of water. drought is a prolonged period with with little or no rainfall.
A
Floods and Droughts
Floods
and droughts are considered hazards as they can adversely affect lives and property.
Floods The
occurrence of floods can be due to both natural and human causes. Natural causes of floods include: Excessive
rainfall Storm surges Melting snow Global atmospheric processes Movements of the Earth¶s surface
Floods The
occurrence of floods can be due to both natural and human causes. Human causes of floods include: Clearing
of forests Urban development Enhanced greenhouse effect
Natural
Causes of Floods
Excessive rainfall: Floods occur when rainwater is unable to seep into the ground quickly enough, or rivers overflow their banks because river channels cannot contain e xcess water. Common in places experiencing tropical
climate.
monsoon
Natural
Causes of Floods
Storm
surges: Occurs when strong winds raise the waves in the ocean to e xceptionally high levels, causing them to crash onto the coast and flood the land. Common
relief.
in coastal areas and places with low -lying
Natural
Causes of Floods
Melting
snow: Melting of snow in spring releases large amounts of water into the rivers, causing them to overflow their banks. Common
in places experiencing cool temperate climate.
Natural
Causes of Floods
Global atmospheric processes: Abnormal weather phenomena such as result in floods or droughts. El
El
Niño and La Niña can
Niño is the warming of surface ocean waters at the southeastern part of Pacific Ocean. temperature of ocean off the coast of South Surface temperature America heats up. Air above oceans becomes hot and humid. Extreme weather like heavy rain and thunderstorms in South America result.
Natural
Causes of Floods
Movements
of the Earth¶s surface: Earthquakes can bring about landslides or trigger off tsunamis. When
landslides landslides occur, loosened soil may be deposited in rivers, causing overflowing of these rivers. Tsunamis triggered by strong undersea earthquakes can flood and devastate coastal settlements.
Human Causes of Floods
Clearing of forests ±
±
±
Lack of vegetation cover to hold the soil together on slopes. Soil is thus eroded and deposited in rivers, making them shallower. Bare slopes increase surface runoff and volume of water flowing into rivers. Flooding occurs when rivers overflow.
Human Causes of Floods Urban
development: The clearing of land for development of housing and industries, thus increasing built-up areas. Concrete
pavements and tarred roads prevent rainwater from seeping into the ground. Less natural vegetation is available to intercept the rain. Increase in surface run-off flowing into rivers result in flooding.
Human Causes of Floods Impacts of enhanced greenhouse effect: Human activities are the most likely causes
of enhanced greenhouse gases. Global
warming results in climatic c limatic changes such as higher rainfall, which in turn leads to incidences of floods.
Droughts Droughts
can be attributed to both natural and human causes. Natural causes of droughts include: Delayed
rain or insufficient rainfall Global atmospheric processes
Droughts
Human
causes of droughts
include: Reduced
forest cover Enhanced greenhouse effect Overuse of water
Natural
Causes of Droughts
Delayed rain or insufficient or insufficient rainfall: Occurs mainly in arid or semi -arid regions, and in tropical monsoon regions, when when monsoon winds winds that bring rain are delayed.
Natural
Causes of Droughts
Global atmospheric processes ± El
Niño causes droughts in countries like Indonesia and Australia in the western Pacific. droughts in countries like ± La Niña causes droughts Peru in the eastern Pacific.
Human Causes of Droughts Reduced
forest cover: Reduced vegetation cover results in lower rates of transpiration. Less
water vapour in the atmosphere leads to fewer clouds formed. Soil exposed to direct sunlight dries up quickly.
Human Causes of Droughts Impact
of enhanced greenhouse effect: Global warming can also cause droughts in places with drier climates. High
temperatures increase the rate of evaporation, drying up land, rivers and lakes.
Human Causes of Droughts
Overuse of water: Places with rapid population growth require more water for homes, industry and agriculture. Water
sources sources such as rivers and groundwater groundwater may not be able to sustain the increase in water usage.
Impact
of Floods and Droughts
Floods
and droughts are natural hazards, but not all of them are considered natural disasters.
Impact
on human lives and property varies.
How Floods Affect People and the Environment Loss
of lives: Floods often occur when least expected. People
are often not prepared and thus
drown. Impact is higher near floodplains, which are densely populated soil fertility.
often due to
How Floods Affect People and the Environment
Damage to property and infrastructure: in frastructure: Floods damage homes, roads, power supply etc. Such
damage is very costly and takes a long time to repair.
How Floods Affect People and the Environment Spread
of diseases: Homeless flood victims are housed in makeshift shelters. Crowded
conditions without proper sanitation can cause the outbreak of diseases.
How Floods Affect People and the Environment
Damage to the environment: Trees, vegetation and natural habitats of animals can be destroyed.
How Floods Affect People and the Environment
Fertile soil for agriculture: One benefit of the regular flooding of rivers is that fertile alluvium deposits are produced.
How Droughts Affect People and the Environment
Damage to the environment: Prolonged droughts can cause desertification in arid and semi-arid regions, making the ground dry and barren.
How Droughts Affect People and the Environment
Forest fires and haze: Prolonged droughts cause vegetation in forests to become very dry. Vegetation thus catches fire easily.
Adapting to Floods and Droughts Reducing ± Building ±
the impact of floods
artificial levées or dykes
Construction of dams
± Building
control
± W atershed ± Flood
management
insurance
±
Monitoring and education
±
Post-flood management measures
Reducing Building
the Impact of Floods
artificial levées and dykes
Walls
of sand, sand, stone and concrete are built along river banks to increase the capacity of the river to hold water.
Construction of dams Dams
control the amount of flowing into the rivers, gates to hold back or water.
water using release
Reducing
the Impact of Floods
Building control Maps
showing flood -prone areas provide information for developers to ensure that floods would not affect the buildings they construct.
Watershed
management
Programmes
can be implemented to manage the entire watershed by conserving vegetation cover or re -planting trees so as to reduce surface s urface run-off.
Flood insurance Residents
in flood -prone areas can have their property insured against flood, so that they can afford to repair their property if floods occur.
Reducing Monitoring
the Impact of Floods
and education
Scientists
can use modern technology to monitor weather patterns and warn of floods in advance. Citizens can be educated on how to react when floods occur.
Post-flood management measures Plans
can be made by authorities authorities to evacuate victims when floods occur. Foreign aid may also be to help flood victims.
offered
Adapting to Floods and Droughts Reducing
the impacts of droughts
±
Management of watershed and agricultural practices
±
Using proper irrigation techniques
±
Cloud seeding
±
Post-drought management measures
Reducing Management
the Impact of Droughts of watershed and agricultural
practices Plans
such as the Agenda 21 report teaches countries on how to manage their watershed. Effort is put in to increase vegetation in drought -affected areas in order to prevent desertification. c an be planted. Crops that are more resistant to droughts can Using
proper irrigation techniques
Irrigation
brings water to areas through the use of man made channels. Proper irrigation minimises water loss, and helps conserve water.
Reducing
the Impact of Droughts
Cloud seeding Cloud
seeding induces the formation of rain. Substances that enable water droplets to form more easily are dispersed into the air by aeroplanes.
Post-drought management measures International
aid organisations can provide money, food and water to countries affected by drought.
Living
with Floods and Droughts
Preparation is key! Occurrences
of floods and droughts can never be fully prevented.
We
can instead prepare for them and reduce the negative impacts that they bring.
Technology
can help to better manage floods and droughts.
