GEOGRAPHY
NOTES
WEATHER and CLIMATE
Weather Hazards
The term weather hazard refers to an abnormal or extreme weather
condition that poses a threat to life and result in discomfort and even loss of
life.
Common weather Hazards.
Floods
Drought
Lightning
Tropical cyclones
Floods
The term flood refers to water that flows over the banks of the river
when the carrying capacity has been exceeded.
In such a situation the river channel can no longer hold the water and
it overflows the banks. Causes of floods. Floods are caused by heavy
rainfall of about 250 mm in 12 hours.
Floods may also be caused by melting of ice. Human activities may
also contribute to flooding through the following ways:
Creation of concrete surfaces especially in urban areas which result in
reduced infiltration and increased surface runoff.
Deforestation which leaves the land bare, increasing surface runoff.
Poor farming methods such as monoculture and stream bank
cultivation which promote soil erosion, lead to siltation of rivers thus
reducing the depth of the river.
Poorly constructed dam walls which often burst and cause flooding
downstream.
Overgrazing which causes soil compaction resulting in increased
surface runoff.
Effects of floods.
Floods have both positive and negative effects.
, A. Positive effects.
Floods help to recharge ground water.
Floods enrich the soils due to increased nutrients.
Floods results in diverse ecosystems due to availability of water and
enrichment of the soil.
Floods result in increased fish therefore promoting fishing activities.
B. Negative effects
Floods may result in drowning of people and loss of people’ lives.
Floods results in destruction of homes and loss of property.
It may results in washing away of crops or waterlogging, thus causing
food shortages.
Floods cause soil erosion and result in land degradation.
Floods may result in the death of livestock as well as wild animals.
Floods are associated with the outbreak of waterborne diseases such
as malaria.
Floods may destroy infrastructure such as transport network systems,
power lines and bridges.
floods may result in water pollution, thus causing water shortages.
Measures to reduce the effects of floods.
People should build homes on highlands, far from floodplains.
Building of canals or artificial channels to divert water away from
settlements.
Building artificial levees or embankments on river banks to increase
the carrying capacity of the channel. -Planting vegetation of catchment
areas to reduce surface runoff.
People may be encouraged to sack sand bags around the houses to
prevent water from flooding into them.
Introduction of early warning systems which help people to be
prepared for floods.
Widening and dredging river channels so that they hold more water.
Relocating people to higher grounds.
Straightening river channels to increase its speed and reduce water
overflowing from meanders and marshy areas.
Educating people about the causes and ways of reducing impacts of
floods.
Resettling people to areas that are less prone to flooding.
Drought
NOTES
WEATHER and CLIMATE
Weather Hazards
The term weather hazard refers to an abnormal or extreme weather
condition that poses a threat to life and result in discomfort and even loss of
life.
Common weather Hazards.
Floods
Drought
Lightning
Tropical cyclones
Floods
The term flood refers to water that flows over the banks of the river
when the carrying capacity has been exceeded.
In such a situation the river channel can no longer hold the water and
it overflows the banks. Causes of floods. Floods are caused by heavy
rainfall of about 250 mm in 12 hours.
Floods may also be caused by melting of ice. Human activities may
also contribute to flooding through the following ways:
Creation of concrete surfaces especially in urban areas which result in
reduced infiltration and increased surface runoff.
Deforestation which leaves the land bare, increasing surface runoff.
Poor farming methods such as monoculture and stream bank
cultivation which promote soil erosion, lead to siltation of rivers thus
reducing the depth of the river.
Poorly constructed dam walls which often burst and cause flooding
downstream.
Overgrazing which causes soil compaction resulting in increased
surface runoff.
Effects of floods.
Floods have both positive and negative effects.
, A. Positive effects.
Floods help to recharge ground water.
Floods enrich the soils due to increased nutrients.
Floods results in diverse ecosystems due to availability of water and
enrichment of the soil.
Floods result in increased fish therefore promoting fishing activities.
B. Negative effects
Floods may result in drowning of people and loss of people’ lives.
Floods results in destruction of homes and loss of property.
It may results in washing away of crops or waterlogging, thus causing
food shortages.
Floods cause soil erosion and result in land degradation.
Floods may result in the death of livestock as well as wild animals.
Floods are associated with the outbreak of waterborne diseases such
as malaria.
Floods may destroy infrastructure such as transport network systems,
power lines and bridges.
floods may result in water pollution, thus causing water shortages.
Measures to reduce the effects of floods.
People should build homes on highlands, far from floodplains.
Building of canals or artificial channels to divert water away from
settlements.
Building artificial levees or embankments on river banks to increase
the carrying capacity of the channel. -Planting vegetation of catchment
areas to reduce surface runoff.
People may be encouraged to sack sand bags around the houses to
prevent water from flooding into them.
Introduction of early warning systems which help people to be
prepared for floods.
Widening and dredging river channels so that they hold more water.
Relocating people to higher grounds.
Straightening river channels to increase its speed and reduce water
overflowing from meanders and marshy areas.
Educating people about the causes and ways of reducing impacts of
floods.
Resettling people to areas that are less prone to flooding.
Drought
