1. Causes of floods Description Example
- Places which experience the
- The Yangtze River and the
tropical monsoon climate have
Yellow River in China freq-
seasons of heavy rain.
uently overflow their banks
Excessive rainfall because of the deposition of
- When excess rainwater cannot be
sediments washed into the
held by the river, the river over-
river, reducing the depth and
flows their banks and floods the
ability of the river to contain
surrounding areas.
water.
- Can cause floods in coastal areas.
- Bangladesh is a low-lying
- Strong winds raise the waves in country with mostly sits on
the ocean to higher levels which low-lying floodplains of Brah-
Storm surges mahputra and Ganges Rivers.
crash onto the coast, flooding the
land. Due to its low elevation, it is
frequently flooded by storm
- Esp during tropical storms. surges from the Bay of Bengal.
- Places which experience the cool
- In 1986, the St John River
temperate climate have winters
in Canada flooded the
followed by spring.
surrounding areas as it could
Melting snow - In spring, the melting snow flows not hold the excess water from
into rivers increasing the volume of melting snow. Several homes
water in the rivers, the river over- were submerged and families
flows their banks and floods the were evacuated.
surrounding areas.
- El Niño: rise in air pressure over
- In 1997-98, El Niño brought
Indian Ocean where INA, AUS are
heavy and prolonged rains to
causes a fall in pressure over PER.
Peru for several months, Piura
Tradewinds move eastwards from
River in Peru overflowed its
SW of Pacific to SE of Pacific.
banks to flood surrounding
This pushes warm surface waters
areas.
eastwards along with winds. It
brings droughts to SW Pacific and
heavy rains to SE Pacific, causing
floods in SE Pacific.
Global atmospheric processes
(El Niño and La Niña) - La Niña: fall in air pressure over
Indian Ocean where INA, AUS are
causes a rise in pressure over PER.
Tradewinds move westwards from
SW of Pacific to SE of Pacific.
This pushes warm surface waters
westwards along with winds. It
brings heavy rains to SW Pacific,
causing floods in SE Pacific and
droughts to SE Pacific.

2. - Earthquakes results in landslides - In 2004, the Indian Ocean
where soil is loosened and it flows Tsunami triggered by a strong
down. When soil is deposited into undersea earthquake, destroy-
rivers, it reduces the depth and ed Banda Aceh, Indonesia, a
ability of the river to contain water coastal town.
Movements of the Earth’s surface and the river overflows its banks to
flood the surrounding areas.
- Earthquakes can also trigger
tsunamis that destroy coastal sett-
lements.
- Without vegetation, no roots can - Forests in mountainous
hold soil together. Soil erosion regions of China are cleared
increases. for housing and firewood. This
has causes more floods in
- Increases surface runoff as the China.
ground is bare.
- Forests are also cleared in
- With more surface runoff, it Bangladesh causing more
Clearing of forests
increases the volume of water sediments to be deposited in
flowing into the rivers. the Ganges and Brahmaputra
Rivers leading to more floods.
- Soil and mud are deposited in the
river, reducing the depth and the
ability of the river to contain water
and the river overflows its banks to
flood the surrounding areas.
- More land is cleared for urban - Areas around River Thames,
development as population London experience regular
increases hence there are more flooding as the natural
impermeable surfaces (eg. vegetation has been cleared for
Urban development concrete pathways, tarred roads) concrete pathways hence more
hence greater surface runoff that surface runoff, causing River
leads to increased river volume Thames to overflow its banks
which soon overflows causing a and the surrounding areas.
flood.
- Increase in global average
temperatures cause the melting of
Impacts of enhanced
ice covers that rises the sea levels. -----------
greenhouse effect
The excess water then floods low-
lying areas in the world.

3. Causes of droughts Description Example
- Places which experience the - Countries such as India and
tropical monsoon climate have Bangladesh experience droughts
seasons of very little rain. when the Southwest Monsoon is
Delayed or insufficient rainfall delayed in June or the Northeast
- When monsoonal winds are Monsoon is delayed in
delayed, the dry season is December.
prolonged and droughts occur.
Global atmospheric processes - REFER TO EARLIER NOTES. - REFER TO EARLIER NOTES.
- Reduced vegetation reduces - Deforestation in Amazon TRF
rates of transpiration and the led to worst droughts in Amazon
amount of water vapour drops. Basin in 40 years.
- Less clouds are formed when - Water levels are so low that
Reduced forest cover less water vapour condenses and exposed river banks dried up and
less rain falls. are eroded by wind.
- Direct heating onto the soil
dries it up even faster and the soil
becomes dry.
- Can cause droughts in places - In Sahel, Africa, high
with drier climates. temperatures evaporate water
quickly, drying up lakes and
Impact of enhanced
- Also caused by increase in rivers. Due to the scarcity of
greenhouse effect
emissions of greenhouse gases water, little rain falls over a long
that increase the global average period of time causing droughts.
temperatures.
- Overpopulated areas have high - Since 2001, Kothariya, India
demand of water hence the use of have been experiencing a drought
water for agriculture, homes and due to the overuse of water and
Overuse of water
industries exceed what the water the scarcity of water which they
sources can provide. get from 5 water holes dug into
the floors of ponds.

4. Impacts of floods Description Example
- Floodplains are attractive places - In 2003, weeks of heavy
for cultivation of crops due to the downpour led to rising flood-
deposition of fertile alluvium waters in north-central Huai
hence these places are densely River Basin in China which
populated. claimed 298 lives and forced
Loss of lives (-) many to evacuate.
- When floods occur in these
places, impact of it is amplified.
Also, floods occur when people
least expect them hence they
drown in a flood.
- When floodwaters submerge - Hurricane Katrina hit Gulf
towns and villages, homes and Coast of USA causing
infrastructure are destroyed. massive flooding esp to New
Homes are destroyed. Roads are Orleans with US$44 billion of
Damage of property
inaccessible. Power supply and damage.
and infrastructure (-)
telephone lines are disrupted.
- Such damages require high costs
and long times to fix.
- Homeless flood victims are
housed in overcrowded makeshift
shelters lacking in sanitation and
Spread of diseases (-) ---------
clean drinking water. Outbreak
of diseases (eg. malaria and
cholera) are common.
- Floods destroy trees and other - On 17 July 2006, a tsunami
plant life, as well as natural that struck Java caused
habitats of animals. severed damage to coastal
ecology along the southern
Damage to environment (-)
part.
- Nature reserve near
Pangandaran Beach was
badly affected.
- Regular flooding of the rivers - People live around the Nile
provide floodplains with fertile Delta in Egypt as the river
Fertile soil for agriculture (+) alluvium, “fertilising” the soil. provides fertile alluvium for
cultivators to grow their
crops.

5. Impacts of droughts Description Example
- Lack of water in rivers and - In mid 1980s, more than 3 mil
lakes causes people and animals people died from starvation and
Shortage of food and water to die from dehydration and dehydration in the drought-
crops are destroyed, leading to stricken Sahel region of Africa.
starvation and famine.
- Desertification occurs when - Sahara Desert has expanded
deserts spread into areas with southwards since 1968.
Damage to the environment little or no rain leaving dry and
barren soil that is unable to - According to UN, deserts are
support veg growth. spreading at 80000km2/year.
- Heat dries the veg which
catches fire easily and causes
haze which spreads by wind.
Forest fires and haze --------
- Cause breathing difficulties and
eye irritations in people living in
cities surrounding it.
Adaptation to floods Description + - Examples
- Walls of sand, - Increase - Easily over- - In China, dykes
stone and concrete capacity of river, topped by a have been built in
are built along river reducing chances higher flood the lower course
banks which are of flood hence it will pro- of the Yellow
prone to flooding tect the area River. Always
Building artificial overflowed due
levees or dykes - Constant dep- to constant
osition of sedi- deposition of
ments reduce the sediments in the
depth of the river, soil.
reducing the vol-
ume of the river
- Walls of dams - Controls amt of - Very expensive - Series of dams
have gates to hold water flowing to construct and in Tennessee
back or release downstream into must be well- Valley in USA
Construction water. Forms an art- the river, prevent- constructed to spent $281 mil
of dams ificial reservoir ing a flood down- prevent collapse
behind the dam stream
-Hydroelectricity
can be generated

6. - Maps drawn up by - Reduce areas - Difficult to - In Singapore,
local governments to prone to flood- carry out in ur- Ministry for En-
show areas prone to ing as govern- ban areas facing vironment and
floods ment would raise land constraints Water Resources
the ground levels as there is a dem- (MEWR) requi-
Building control
- Contain valuable or by having a and for land res ground levels
info for developers drainage system to be raised, dra-
to construct their inage canals to
buildings at safe be improved
places
- Conservation of - Most environ- - Requires strict - Royal Forest
vegetation cover mentally friend- supervision to Department
reduces surface ly way of reduc- patrol watersheds (RFD) in
runoff and reduces ing floods as Thailand
soil erosion, no there are no - Wardens may developed a
Watershed deposition and no changes to the be corrupt and watershed prog-
management reduction in river environment. accept bribes ramme to prevent
depth from companies floods from
who want to cut occurring.
- Replanting of trees the trees down
in watersheds is
done to manage it
- Residents living in - Provides finan- - People in LDCs - United King-
flood-prone areas cial resources for cannot afford to dom has a
can buy flood the rebuilding of pay the annual national flood
insurance that gives houses after the premiums and insurance
Flood insurance them financial res- flood may not have it. programme to
ources to rebuild provide financial
after the flood help to people
who lost their
homes.
- With modern tech- - When detected - Usually - In USA, when
nology, scientists early, evacuation response is not floods are ex-
can monitor weather can be carried fast enough to pected, govern-
patterns and issue out to reduce loss evacuate all the ment advises
warnings prior to the of lives people to safer people to leave
Monitoring flood grounds hence their homes to
and education some still die safer grounds
- Countries have
evacuation plans
that are informed via
media to the public
so that they can
evacuate

7. - Plans made by - Not reliant on - Not immediate - During Hurri-
authorities to country’s efforts and takes time for cane Katrina,
evacuate flood alone, other aid to arrive, by USA opened
victims and provide countries and or- then some more Louis Armstrong
humanitarian aid to ganisations can would have died New Orleans
survivors also help to Airport to receive
Post-flood
reduce more loss humanitarian and
management
of lives rescue operations
strategies
- Aid is sent by
countries such as
China and organ-
isations such as
UN
Method against
Description + - Examples
droughts
- Agenda 21 rep- - Chances of - Some crops - In Israel, apple
ort teaches count- desertification cannot be substi- cacti, which bears
Management of
ries how to man- reduced tuted as they are a fruit 11 out of 12
watershed and
age watersheds culture in the months, is grown
agricultural
and the need to country as they require less
practices
change agricultural water
practices
- Proper irrigation - Less water is - Irrigation must - In Turkey, farms
techniques through wasted hence be carefully done use spray
Using proper the use of man- demand is less to prevent over- or irrigation where
irrigation made channels under- that will precision
techniques reduce water loss - More water is both waste water sprinklers drip
conserved for small amounts of
times of drought water onto crops
- Spraying of - When successful, - Cost of cloud - In Malaysia and
silver iodide or it can bring rain seeding is very Thailand, cloud
dry ice using to drought-stricken high, LDCs cannot seeding was used
planes or machines areas to reduce afford to pay large in 2005 to relieve
on ground into the impact of drought sums to overcome the one of the
Cloud seeding sky to act as drought worst droughts that
condensation was affecting rice
nuclei for water - Silver iodide can harvests
droplets then cause temporary
clouds to form and incapitation in
rain to fall humans

8. - Aid from - Not reliant on - Not immediate - US Agency for
countries and country’s efforts and takes time for International
international aid alone, other aid to arrive, by Development
organisations is countries and or- then some more provides donations
sent to drought- ganisations can would have died of money, food
stricken areas to also help to reduce and water to
help them more loss of lives Ethiopia in the
2006 drought
Post-drought
management - Food for the
measures Hungry Relief
brought in water
via tanker trucks to
provide water to
school cisterns so
that they can
benefit from the
emergency water
provision during
the same drought.