IDSB02: Lecture 8 - Dryland Environments and Development. March 1st, 2017
● Found between the tropical convergence zone and the great deserts.
● In the northern hemisphere, summer is a semi-arid wet season (within the ITCZ) and
winter is the dry season under the STHPZ.
● Tropical grasslands with scattered trees.
● PET > Precipitation.
● Deserts, arid, or semi-arid lands.
● Occupy about 41% of global terrestrial area.
○ Home to 38% of the Earth’s population.
○ One of the world’s most heavily inhabited ecosystems.
● Defined by very low precipitation (< 1000 mm/yr).
Precipitation of Regional climates:
● Arid (<200 mm/y).
● Semi-arid (200 - 1000 mm/y).
● Wet tropics (> 2500 mm/y).
● Drylands are a large and important region, particularly in sub-Saharan Africa.
● Livelihoods are dominated by environmental constraints:
○ Low water availability/ water cycles.
○ Limited availability of soil nutrients.
○ Soil erosion.
● Highly developed, context specific, local bodies of environmental knowledge are needed
to manage properly.
Proximate Causes of Land Degradation in Semi-arid Environments:
● Rainfall and poor tillage practices.
● Changes in crop types:
○ Shift in production during climatic anomalies due to a few years of good rain.
○ Leads to degradation after the anomaly ends.
● Excessive growth of cattle herds
● Increased demand for fuelwood.
Ultimate Causes of Land Degradation in Semi-arid Environments: ● Any combination of environmental, social, economic and political factors resulting in
increasing sedentarization on lands not suited for it (environmental limits of growth), as
○ Prolonged drought.
○ Increased population.
○ Loss of traditional ecological knowledge.
○ Effects of the good rainfall years.
Forms of Dryland Livelihoods:
● Agriculture-based livelihoods.
● Pastoralism, nomadic livestock herding, animal husbandry.
● Key livestock species that are adapted to arid conditions are camels, goats, sheep, and
● Manage extreme spatially and temporally variable resources.
● The seasonal migration of animals/herders allows for the capture of moisture and soil
fertility and then moving before resources are exhausted.
● Dominant reason for migration is to find better pasture.
● Requires very complex local knowledge.
○ Long-term experience of regional environmental variability.
● Access to different lands necessary to traverse during migrations.
● Navigating lands governed by various schemes, from common property to private
● Highly dynamic environmental-human systems.
● Desertification: is a decrease in land quality that has become widespread in semi-arid/
● Initially blamed on exceeding the land’s “carrying capacity”.
● Soils have been sustainable for thousands of years, what’s changed?
● Western narratives suggest it’s strictly mismanagement.
Drought x Wind - “The Dust Bowl”:
● In the early 20th century when a lot of the prairies can been settled, widely for
○ The grasslands in the prairies were dug up and turned into crop rotations in large
● Around this time there was the economic depression as well as decade long droughts. ○ This meant that farmers had years without crops or money.
● A lot of farmers stopped their agricultural businesses and abandoned their bare
○ Wind caused erosion of all this soil due to no protection of the bare soil.
Conclusions From the “The Dust Bowl”:
● The dust bowl experience results in several conclusions about drylands in developing
○ Degradation was a one-way trend from intact, “climax ecosystems” to deca