Causes of Drought

Question 1

How do humans increase drought risk? (6)

Answer 1

1. over abstraction
2. deforestation
3. reservoir construction
4. over grazing
5. climate change
6. water transfer scheme

Question 2

How does reservoir construction increase drought risk?

Answer 2

reduces channel flow causing drought down stream, evaporation rates increase due to a large body of water

Question 3

How does deforestation and over grazing lead to increased risk from drought?

Answer 3

deforestation for grazing leads to less vegetation so reduced evapotranspiration so precipitation falls less. Additionaly organic matter is reduced due to lack of leaf litter and soil compacts which prevents infiltration and surface runoff

Question 4

What has caused increased drought risk in the sahel region? (5)

Answer 4

1. air pollution caused by Europe and North America
2. higher sea surface temperature
3. El Nino
4. increasing demand due to population growth
5. overcultivation and over grazing

Question 5

define drought

Answer 5

an extended period of deficient rainfall relative to the long term statistical average for a region

Question 6

What are the four types of drought?

Answer 6

1. meteorological
2. agricultural
3. hydrological
4. socioeconomic

Question 7

What is meteorological drought?

Answer 7

when long term precipitation is much lower than normal

Question 8

What is agricultural drought?

Answer 8

When there is insufficent soil moisture to meet demands of crops

Question 9

What is hydrological drought?

Answer 9

when there are deicencies in surface and subsurface water supplies

Question 10

What is socioeconomic drought?

Answer 10

when the water demands from people and industry exceeds supply

Question 11

Why are the sub tropics prone to drought?

Answer 11

Air that had risen at the equator has cooled and sinks to form a belt of high pressure which results in hot, dry conditions

Question 12

Where do the subtropics recieve their rain from?

Answer 12

From the ITCZ when it moves north or south, depending on the tilt of the earth.

Question 13

When do the sub tropic regions become drier than normal?

Answer 13

The decending part of the Hadley cell blocks the high humidity, rain bearing air masses, modifying the pattern of wet and dry seasons

Question 14

What is the ITCZ?

Answer 14

The Intertropical Convergence Zone

Question 15

What is the order of the cells from the ITCZ out?

Answer 15

1. Hadley Cell
2. Ferrel Cell
3. Polar Cell

Question 16

Why do the mid latitudes have a temperate climate?

Answer 16

cold air from the poles moves towards the mid latitudes

Question 17

Why are the polar regions areas of high pressure?

Answer 17

The desention of cold air due to lack of solar radiation

Question 18

How are blocking anti-cyclones formed?

Answer 18

loops in the jet stream create a stable area of high pressure

Question 19

What happens as the result of blocking anti-cyclones?

Answer 19

rain bearing depressions are forced around the anti-cyclones, diverting frontal rainfall away for up to two weeks

Question 20

What is ENSO?

Answer 20

A naturally occuring large mass of very warm seawater in the equatorial pacific ocean

Question 21

What happens to areas where ENSO is located?

Answer 21

Evaporation rates are higher and precipitation is greatet, while areas of cooler water have drier weather

Question 22

What happens during an El Nino event?

Answer 22

reduces precipitation in the western Pacific, and the affected countries experience drought

Question 23

When does La Nina occur?

Answer 23

when the warm mass of water is pushed even further west than normal

Question 24

What are the effects of La Nina?

Answer 24

Droughts caused in areas such as Peru and California

Question 25

What are the two phases of ENSO?

Answer 25

El Nino and La Nina