5.4B - Human Activity and Drought
The contribution human activity makes to the risk of drought: over-abstraction of surface water resources and ground water aquifers. (Sahel region or Australia)
People are not the cause of drought, but their actions can make droughts more severe.
Desertification in the Sahel
The Sahel region of Africa stretches from Mauritania eastwards to Ethiopia.
Desertification is the process by which once-productive land gradually changes into a desert-like landscape. It usually takes place in semi-arid land on the edges of existing deserts. It's not necessarily irreversible.
The causes of desertification are essentially natural. They set in motion a downward spiral:
The northern Sahel region is experiencing a 30-40% annual departure from normal rainfall. 25-30% below that, and 20-25% in the southern Sahel.
Human factors act like a feedback loop. Humans enhance the impacts of drought by the over-abstraction of surface water from rivers and ponds, and of groundwater from aquifers. Key human factors encouraging this are:
In the case of the Sahel, the situation has been made worse by frequent civil wars. Crops, livestock and homes have been deliberately destroyed.
Desertification is the process by which once-productive land gradually changes into a desert-like landscape. It usually takes place in semi-arid land on the edges of existing deserts. It's not necessarily irreversible.
The causes of desertification are essentially natural. They set in motion a downward spiral:
- Changing rainfall patterns with rainfall becoming less reliable, seasonally and annually. The occasional drought year sometimes extends to several years.
- The vegetation cover becomes stressed and begins to die, leaving bare soil.
- The bare soil is eroded by wind and the occasional intense shower.
- When rain does fall, it is often only for short, intense periods. This makes it difficult for the remaining soil to capture and store it.
The northern Sahel region is experiencing a 30-40% annual departure from normal rainfall. 25-30% below that, and 20-25% in the southern Sahel.
Human factors act like a feedback loop. Humans enhance the impacts of drought by the over-abstraction of surface water from rivers and ponds, and of groundwater from aquifers. Key human factors encouraging this are:
- Population growth: rapid population growth puts pressure on the land to grow more food. Migrants fleeing from one disaster area help to make another.
- Overgrazing: too many goats, sheep and cattle destroy the vegetation cover
- Overcultivation: intense use of marginal land exhausts the soil and crops will not grow
- Deforestation: trees are cut down for fuel, fencing and housing. The roots no longer bind the soil, and erosion ensues.
In the case of the Sahel, the situation has been made worse by frequent civil wars. Crops, livestock and homes have been deliberately destroyed.
Drought in Australia
Drought is a recurrent annual feature in Australia, with up to 30% of the country affected by serious of severe rainfall deficiency. The link with El Niño events is well established. However, droughts are becoming more frequent and more severe.
The worst event so far has been the 'Big Dry' of 2006. This was assessed as a 1-in-1000 year event and is thought to have been associated with a longer-term climate change.
Unlike the Sahel, Australia has not followed the same downward spiral of desertification. A careful management of scarce water resources, and sorting out the competing demands of irrigation and urban dwellers, has stopped this from happening. Other actions include the large-scale recycling of grey water (waste bath, shower, sink and washing water), constructing desalination plants and devising new water conservation strategies.
The worst event so far has been the 'Big Dry' of 2006. This was assessed as a 1-in-1000 year event and is thought to have been associated with a longer-term climate change.
Unlike the Sahel, Australia has not followed the same downward spiral of desertification. A careful management of scarce water resources, and sorting out the competing demands of irrigation and urban dwellers, has stopped this from happening. Other actions include the large-scale recycling of grey water (waste bath, shower, sink and washing water), constructing desalination plants and devising new water conservation strategies.