True or False?
The distribution of hot arid and semi-arid lands has remained constant over time.
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True or False?
The distribution of hot arid and semi-arid lands has remained constant over time.
False.
The distribution of hot arid and semi-arid lands has changed over time due to changing climates and human activity.
What percentage of Earth's land surface is covered by drylands?
Drylands cover about 40% of Earth's land surface.
Define the term drylands.
Drylands are areas of water scarcity, where rainfall is limited (arid areas) or seasonal (semi-arid), with high temperatures leading to high rates of evaporation and transpiration.
What was the Sahara region like between 11 000 and 5 000 years ago?
Between 11 000 and 5 000 years ago, the Sahara region was known as the Green Sahara with lakes, lush vegetation and animals of the savanna biome such as elephants and lions.
What percentage of the total global population lives in drylands?
More than 38% of the total global population (approximately 2.7 billion people) lives in drylands.
What are the characteristics of a dryland climate?
Dryland climates are characterised by water scarcity, limited or seasonal rainfall, high temperatures, high rates of evaporation and transpiration, and high levels of climatic uncertainty.
State the meaning of climatic uncertainty in the context of drylands.
Climatic uncertainty in drylands refers to the unpredictable nature of rainfall, where many areas can experience drought for several years.
True or False?
Human activity has not influenced the extent and distribution of drylands.
False.
Human activity has influenced the extent and distribution of drylands.
Define desertification.
Desertification is the process of desert-like conditions spreading into what were previously semi-arid areas, as the quality of soil and its fertility declines over time.
What is salinisation?
Salinisation is the process where intense evaporation at the surface results in the capillary rise of soil moisture and minerals, increasing salt content in the soil.
True or False?
Only human activity causes soil erosion.
False.
Soil erosion is a natural process that is made worse by human activity.
What are three main physical changes that contribute to desertification?
The three main physical changes contributing to desertification are:
Lowered precipitation rates.
Increased intensity of precipitation.
Increased temperatures.
Define overgrazing.
Overgrazing is when the number of animals grazing on land exceeds what the land can support, leading to soil degradation.
What is overcultivation?
Overcultivation is growing too many crops without replenishing the soil, causing it to become exhausted.
How does deforestation contribute to desertification?
Deforestation contributes to desertification by removing trees, leading to a loss of roots that hold the soil down, which gives rise to erosion.
What negative consequence arises due to over-irrigation in arid regions?
A negative consequence of over-irrigation in arid regions is that it can lead to raising groundwater levels, causing salts to be dissolved and form a salty crust on the surface, creating an impermeable, infertile layer that is toxic to plants.
How does war contribute to desertification?
War contributes to desertification by destroying crops and animals, leading to famine and environmental degradation.
True or False?
Global changes in food trade have no impact on desertification.
False.
Growth in demand for cash crops has led to the best land being used for these crops, leaving unsuitable land for general food crops, which can contribute to desertification.
What is the downward spiral pattern that follows once desertification starts?
The downward spiral pattern is:
Soil degradation → soil erosion → reduced agricultural output → malnutrition, famine → migration → conflict → soil degradation.
How does desertification affect biodiversity?
Desertification affects biodiversity through loss of topsoil, over-exploitation of resources, destruction of vegetation, depletion of water sources, and increased soil salinity.
True or False?
Desertification increases sand-dune formation.
False.
Desertification reduces sand dune formation as there is less vegetation to trap loose material.
What are the social impacts of desertification?
The social impacts of desertification include:
Dust clouds affect air quality and health.
Reduced water supplies increase water-borne diseases.
Forced migration.
Disputes between herdsmen and farmers for limited land.
Food shortages lead to malnutrition and famine.
How does desertification affect agricultural productivity?
Desertification reduces agricultural productivity, leading to long-term declines in crop yields, livestock yields, plant standing biomass, and plant biodiversity.
Define intermediate technology in the context of addressing desertification.
Intermediate technology is a middle ground between low- and high-tech farming methods, using accessible and appropriate technology to help people cope with natural changes and prevent further degradation.
What are diguettes?
Diguettes are a line of stones laid along the contours of sloping farmland to catch rain, allow water to seep into the soil, prevent soil erosion, and retain organic matter.
How does agroforestry help combat desertification?
Agroforestry combines agriculture with forestry, which decreases deforestation, provides shade, increases infiltration and interception, reduces soil erosion, and adds nutrients to the soil.
What is a water-spreading weir?
A water-spreading weir is a structure that gently spreads available water further across the land, reducing soil erosion from runoff when it rains.
True or False?
Desertification is easily reversible if rainfall increases.
False.
Desertification is a very difficult process to reverse, even if rainfall increases. The environment can start to recover with increased rainfall, but it's a slow process.