EGS Frank Week 7 Drylands Flashcards
Desertification definition:
- Process by which land becomes a desert as a result of various factors
- Involves Land Degradation (soil & vegetation) in arid, semi arid & sub humid areas, caused at least partly by humans
- Reduces both resilience & productive potential
- Can neither be readily reversed by removing the cause
nor easily reclaimed without substantial investment
Overview P1/3
- (1) Deserts are home to the () of the () & subject to () which is the () from () conditions & is diff. from ().
- (2) Desertification is of () in many of the (), especially () that have () and can ().
- (3) Desertification is usually not () with () but with the () & ().
- (1) Deserts are home to the descending air of the Hadley Cell & subject to drought which is the deviation from average rainfall conditions & is diff. from just having dry conditions.
- (2) Desertification is of great concern in many of the world’s deserts, especially desert margins that have a reasonable amount of water and can accomodate human activity.
- (3) Desertification is usually not concerned with moving sand but with the degradation of soils & vegetation cover.
Overview P2/3
- (4) It has caused the () of the () and is common in the (), home to () & () of ().
- (5) This DIMINISHES the (), especially if () present & () collected.
- (6) Quite often the impact is () by the () & the () of ().
- (4) It has caused the US Dust Bowl of the 1930s and is common in the Sahel Region, home to dense rural pops. & long periods of drought.
- (5) This DIMINISHES the nutrient content, especially if livestock present & fuelwood collected.
- (6) Quite often the impact is enhanced by the lack of mobility & the loss of semi-nomadic lifestyles
Overview P3/3
- (7) In South Africa, desertification is () by () & (), but also by () in (), with the () & (), which () on () & ().
- (8) In South Africa, it has been noted that there has been a () & () in the () in drought years.
- (9) The LARGEST CAUSE of Land degradation in drylands is the () and ().
- (7) In South Africa, desertification is manifested by erosion gullies & soil erosion, but also by changes in veg. cover, with the placement of boreholes & fences, which increase pressure on veg. & soil cover.
- (8) In South Africa, it has been noted that there has been soil cover loss & vast dust plumes in the Free State in drought years.
- (9) The LARGEST CAUSE of Land degradation in drylands is the persistent pressure & loss of nomadic lifestyles.
Where on earth do we have desertification?
(1)
(2)
(3)
(4)
(5)
(6)
- Along the tropics (above & below equator)
- Desert margins (are vulnerable)
- US Dust Bowl
- Sahel Region
- Southern Africa
- Loess plateau terraces in China
1/4
Causes of Desertification P1:
(1)
(2)
(3)
(4)
(5)
(1) Marginal Climate (precip limited & evapo. rates high = vulnerable)
(2) Exceeding capacity & Inability to recover
(3) Lack of mobility (reduced veg. cover & disturbing soil structure).
(4) Overgrazing (reduced veg. cover & disturbing soil structure).
(5) Poor farming techniques (reduced veg. cover & disturbing soil structure).
2/4
Causes of Desertification P2:
(6)
(7)
(8)
(9)
(10)
(6) Desertification worsened around boreholes (grazing pressure & constant use)
(7) Grazing pressure around well points (soil compaction & disturbance & veg. loss).
(8) Construction of Fences
(9) Installation of Windpumps
(10) Creation of Piospheres
3/4
Causes of Desertification P3:
(11)
(12)
(13)
(14)
(15)
(11) Soil Alteration
(12) Soil Degradation
(13) Soil Erosion
(14) Gullies in South Africa
(15) Overcultivation
4/4
Causes of Desertification P4:
(16)
(17)
(18)
(16) Bush encroachment
(17) Deforestation
(18) Sand/Silt Ratio
Elaboration on some causes of desertification
Natural Processes:
* () -> () -> Soil Erosion
Human Activities:
* Dryland Agri -> () -> () -> () -> Soil Erosion
- Dryland Agri -> () -> () -> () -> () -> () -> Soil Erosion
- Dryland Agri. -> () -> () -> () -> () -> () -> Soil Erosion
- Energy Demands -> () -> () -> Soil Erosion
- Urbanisation -> () -> () -> () -> Soil Erosion
Natural Processes:
* Drought -> Reduced veg. cover -> Soil Erosion
Human Activities:
- Dryland Agri. -> Pastoral -> Land carrying capacity exceeded -> Pasture Deterioration -> Soil Erosion
- Dryland Agri. -> Arable -> Natural veg. removed -> Poor agri. practices -> Soil organic matter lost -> Soil aggregate breakdown -> Soil Erosion
- Dryland Agri. -> Irrigation -> Poor irrigation practices -> Sedminentation, Salinization, Waterlogging -> Reduced soil fertility -> Reduced veg. cover -> Soil Erosion
- Energy Demands -> Fuelwood cutting -> Deforestation -> Soil Erosion
- Urbanisation -> Pop. concentration -> Stress on land -> Degradation of veg. cover -> Soil Erosion
Types of Droughts:
- Meteorological Drought
- Agricultural Drought
- Hydrological Drought
Types of Drought
(1) Meteorological:
- Usually defined based in the degree of dryness (in comparison to some “normal” or avergae) and the duration of the dry period
- Drought onset generally occuse with a meterological drought
Types of Drought
(2) Agricultural:
Links various characteristics of meterological (or hydrological) drought to agricultural impacts, focusing on precip. shortages, soil water deficits, reduced ground water or reservoir levels needed for irrigation, etc.
Types of Drought
(3) Hydrological:
Usually occurs following periods of extended precipitation shortfalls that impact water supply (i.e. streamflow, reservoir and lake levels, ground water), potentially resulting in significant societal impacts
Impacts of desertification:
(1)
(2)
(3)
(4)
(1) Can lead to conflict over resources (water, food) - Local & Global
(2) Health Hazard (plumes)
(3) Forced relocation/mass-migration
(4) Loss of biodiversity
How do we measure desertification?
(1)
(2)
(3)
(4)
(1) MODIS - view dust streaks
(2) 250 meter MODIS/NDVI Time Series Database from the Global Agriculture Monitoring (GLAM) Project
(3) NDVI - shows season variability degradation
(4) Meteosat -SEVIRI pink “dust” scheme
