DroughtLearning objectives:• Specific climatic conditions leads

to drought• Natural hazards occur when

events adversely affect people• Droughts are responsible for

hazards such as crop failure, famine, wildfires

What does this image tell you about where

drought occurs?

WHAT IS DROUGHT? In the UK an official drought is declared

when at least 15 consecutive days go by without more than 0.2mm of rain.

In the Sahel, a drought is declared when there’s below average rainfall for 2 years. The Sahel has actually suffered drought for most of the last 30 years.

DROUGHT HAZARD IN LEDCS Drought is often quoted as one of the

major natural hazards of the developing world

Drought killed just under 10 million in China in 1878.Drought is different from other hazards unlike floods and tropical storms it never kills people directly

TEST BITE Drought is declared in the UK when 15

consecutive days go by with no more than how much rainfall?

When is drought declared in the Sahel? How is drought different to other

climatic hazards?

GLOBAL ATMOSPHERIC CIRCULATION On a global scale drought prone areas can be predicted with accuracy Tropical high pressure zones will have low rainfall as air descends e.g. Sahara desert Whilst these areas are drought prone their lack of rainfall is not seen as natural hazard as the populations there are very small and dispersed

SO WHERE IS IT SEEN AS A NATURAL HAZARD?

Drought is mostly a hazard in the semi-arid regions adjacent to the desert areas. Here seasonal rainfall allows agriculture and has sustained a large population.Millions of people are therefore affected by any change in the pattern of rainfall

THE SAHEL This is the semi arid region south of the

Sahara consisting of 6 countries: Senegal Mauritania Mali Burkina Faso Niger Chad

TEST BITE Why are droughts in desert areas such

as the Sahara not a natural hazard? In which areas is drought the biggest

hazard? Name the 6 countries in the Sahel

region of Africa.

THE SAHEL REGION HAS A WET AND A DRY SEASON DEPENDING ON THE POSTION OF THE ITCZ (INTER TROPICAL CONVERGENT ZONE)

HOWEVER Sometimes the wet season does not

arrive or lasts a shorter than usual time The ITCZ does not migrate as far North

as it usually does. This is due to the influence of sea

temperatures.

TEST BITE What does ITCZ stand for? Why is it important to the Sahel? What causes the failure of the wet

season?

EL NINO Watch the video and then explain how

this phenomenon causes drought.

DESERTIFICATION. Drought is often worsened by ecosystem

degradation Over cultivation – takes too much nutrients from

the soil results in erosion leading to desertification Overgrazing – animals eat plants soil no longer

protected Decline of traditional nomadic lifestyle due to

conflicts and changes in farming due to pressure of increased population.

Removal of bushes and small trees for fuel meeting the demand of an increased population

TEST BITE~ COPY AND EXPLAIN EACH FACTOR

overgrazing

Over cultivation

Over population

Decline of traditional nomadic herders

desertification causes

CAUSES IN THE UK Long periods of high atmospheric pressure

(anticyclones) clouds don’t form so it doesn’t rain.

Long periods of high temperatures. This means more evapotranspiration than precipitation.

Land use e.g. agriculture uses a lot of water High population density strain on resource Changes in the way we live, and increasing

wealth e.g. power showers, dishwashers.

DROUGHT HAZARD IN MEDC Disrupts lifestyles – Watch the video clip 2003 European heat wave sparked

wildfires in Portugal which killed people. Harvests fell dramatically.

Water tables fall small rivers dry up can affect aquatic life

TEST BITE What are the 5 causes of drought in the

UK?

TECHNOLOGICAL RESPONSES TO DROUGHT

Improved forecasting – monitoring El Nino and other surface temperature anomalies may give an advance warning of droughts caused by complex atmospheric circulations.

Ecosystem monitoring – spots early signs of land degradation

Improved water conservation – low tech e.g. stone piles or bunds, agroforestry. High-tech drip irrigation, increase fertilizers, genetically engineered crop varieties.

OTHER RESPONSES Water rates increase Free installation of water saving

devices Non essential uses banned e.g. hose

pipe Reclaim water from sewage treatment

plants. Repair water pipes Build reservoirs in wetter places and

pipe to more populated areas

PLENARYDo you feel that you could answer the exam question given?

Do you think that “test bite powerpoint talk” is a good way to learn?

Homework answer the exam question