5.4 Flashcards
What are the 4 types of drought?
Meteorological drought
Agricultural drought
Hydrological drought
Famine drought
What is meteorological drought?
Short term variability in weather patterns within a long term average pattern occurs
What is agricultural drought?
Reduced groundwater levels after period of dry/hot weather due to continued falling of evaporation occur.
What is hydrological drought?
Lack of rainfall leads to deficiency of soil moisture - impacting plant growth
What is famine drought?
Reduced groundwater levels affect the ability to grow crops
What are the causes of drought (environmentally)
- Global Atmospheric Circulation
- Falling of Inter Tropical Convergence Zone
- Blocking high pressures
- ENSO (El Niño-Southern Oscillation)
What are human causes of drought?
They don’t cause drought, they act as positive feedback.
- Growing environmental degradation - overgrazing by animals
- Deforestation e.g fuelwood
- Population growth has outstripped food production
- Agriculture is rain-fed - making it vulnerable to droughts.
- Abstraction of water from rivers and groundwater
- Building reservoirs reduces the downstream supply of water.
- The removal of vegetation changes the soil conditionstrogh compaction and reduces organic matter and soil moisture retention
What is an example of a human drought?
Ethiopia-Eritrean drought/famine crisis (1999-2000) - about 10 million people needed food assistance.
Why was access to food blocked to many people in Ethiopia and Eritrea?
Because the two countries are at war
Human factors of the Sahel drought
- Human enhanced climate change through the increase in Livestock which can lead to overgrazing
- more vegetation removed = reduced albedo effect = higher surface temp
- More evapotranspiration and reduced condensation
- Over-abstraction of water from rivers/groundwater
- building large reservoirs
- interfering with hydrological cycles
- less vegetation = more soil compaction = less water retention = less infiltration = increases run-off
What are the physical factors of Sahel?
- Low precipitation levels causes vegetation to dry
- decrease in vegetation cover
- warmer surfaces = less soil moisture = higher soil compaction = higher surface run off
- warmer surfaces = higher evapotranspiration
- ITCZ (Inter tropical convergence Zone migrates)
- Subtropical high pressure zone from descending Hadley cell blocking the high humidity, rain-bearing air masses associated with the ITCZ, so that the pattern is modified. This can result in the rains failing and there being a severed drought.
What is the function of a wetland ecosystem?
Habitat or animals
Controls flooding
Can purify water - by removing nitrogen and other pollutants
What is the natural function of a forest ecosystem?
Water storage - regulation of hydrological processes Timber production Wildlife habitat Carbon sequestration Recreational opportunities
Why is global atmospheric circulation a cause of drought?
High pressure air masses are likely to bring about dry, hot areas will low levels of precipitation and clouds. On the other hand, low pressure will bring about wet, cold areas, with high levels of precipitation and clouds.
Why does Inter Tropical Convergence Zone cause drought
The weather found at the ITCZ, is often very wet. It can also migrate, blocking the high humidity, rain-bearing air masses. This can result in rains failing and severe drought.
