Climatic Hazards Revision

-A drought is a prolonged period of time without enough precipitation to support people, animals or crops, resulting in a water shortage.

- Droughts are caused by a shift in the expected weather patterns on a global scale, which causes seasonal rainfall to fail.

-Droughts usually occur where rainfall is seasonal with alternating wet and dry seasons. If the expected rains fail, then there will be no water for crops or grazing.

-Effective precipitation = the difference between the amount of rain that falls and the amount of                                           evapotranspiration.

-Land-locked countries are more likely to suffer from drought, because the rain doesn't get to them.

Main Deserts:

-Atacama

-Nevada

-Arabian

-Sahara

-Australian

-Gobi

-Kalahari

The deserts of the world lie on the two tropics. Those north of the Equator lie on the tropic of Cancer (23½° N), whilst those south of the Equator lie on the Tropic of Capricorn (23½° S). In these latitudes, the prevailing wind direction is from the east. The North-East Trade winds affect deserts to the north, and South-East Trade winds affect deserts to the south. The deserts all lie on the western side of large land masses, so by the time the easterly winds reach them, they will have lost all their moisture and will be dry, bringing no rain.

-The areas with the highest risk of death by drought is in Africa, to the north and south of the equator, in the tropics.

-Also, the areas of medium risk of death by drought are in the very south of Africa, the tropics in Central and South America, plus the tropics in Asia.

-Widespread cutting down of tress for fuel reduces the soil's ability to hold water, drying out the ground, and triggering desertification.

-Constructing a dam on a large river may also cause drought downstream, by severely reducing the flow of water.

-Overcultivation - planting too many crops which use to much water

-Overpopulation - too many people living in an area, using too much water

-Politics - fighting over water or companies being greedy and taking too much water to sell on

-Global warming - weather patterns change (eg. Sahel is becoming hotter and drier)

-El Niño - random weather effect that reverses normal patterns (eg. Australia has years of drought, then years of flooding)

-Weather - increased amount of anticyclone weather (hot and dry) means air holds less moisture, so you get less rain.

-Hotter Weather - more evaporation than precipitation

-The impacts of drought are more severe in LEDCs, as they depend on farming.

-Drought generally lead to famine, especially in LEDCs.

-Droughts and famines can have other geographical impacts. if people are forced to move/migrate in search of water, it can put pressure in other areas

-Food aid on its own is unsustainable

The Sahara desert and Sahel region are now expanding.

Causes:

Natural/Physical:

-Climate Change - since 1960 rainfall totals have been below the long term average for 8 out of 10 years

-Loss of vegetation - As rainfall decreases, there is a reduction in natural vegetation, leaving land open to erosion and loss of topsoil.

Causes:

Human:

-Overgrazing - animals have stripped vegetation away, leaving areas of bare soil.

-Overcultivation - The land is over-used and becomes exhausted and less fertile. Unsustainable farming practices and loss in fertility of soil.

-Deforestation - drys out ground

-Constructing a dam

-Uncontrolled fuel wood collection