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PPT 8 - Coggle Diagram

PPT 8

Droughts in Australia

General info

Drought

The Millenium drought, which lasted from approx. 1996-2010 was among the worst droughts experienced in Australia since European settlement in the 1780s.

Drought commenced with low rainfall in 1996-1997 and worsened in 2001 and 2002. By 2003, it was recognised by the Australian Water and Environment agency as the worst drought on record.

Conditions in Australia remained hot and dry until 2010.

Australia

Australia is vulnerable to droughts because of its geography.

The landmass spans the latitudes of sub-tropical high-pressure belts, meaning that the area usually experiences sinking, dry air and usually clear skies.

Australia is the driest inhabited continent and the rainfall which enters the river system is also very low. On average, only 12% of rainfall flows into rivers in Australia- compared to 52% for North America.

Causes

Human

Water overuse and mismanagement of the Water system in Australia. Excessive water extraction from rivers, especially in the Murray-Darling Basin, reduced water availability. Agriculture, population and industrial use strained the (naturally) limited water resources.

Poor agricultural practices. Irrigation farming in Australia required for the production of cotton placed strain on water supplies. Crops which were not appropriate for the Australian environment were chosen.

Urbanisation. The growing population of Australia, especially in southern cities, led to increased water demand.

Land misuse. Deforestation, land clearing and overgrazing practices degraded areas of land and turned soil into ‘dust pans’ this reduced the ability of the soil to retain moisture.

Physical

ENSO (El Nino- Southern Oscillation). Australia frequently experiences drought during El Nino phases, which leads to reduced rainfall across the country. the drought coincided with multiple El Nino events in the late 1990s and early 2000s.

IOD (Indian Ocean Dipole). Positive phases of the IOD resulted in a lower sea temperature near Australia, reducing evaporation and thus rainfall.

Climate variables. Australia’s climate is naturally dry due to its position in the sub-tropical high-pressure belt. Droughts in Australia are common, even without human intervention.

Reduced rainfall. Australia’s southern regions experienced significantly below-average rainfall. This was particularly challenging for the country as much of Australia’s agriculture is centred in this region.

Human/physical

Climate change. Anthropogenic climate change exacerbated the drought conditions by leading to increased global temperatures. However, this climate change may be (partially) natural in causation.

Changes in rainfall patterns. Climate models indicate that greenhouse gas emissions may have led to changes in the subtropical ridge, blocking rain-bearing systems from reaching southeastern Australia.

Soil moisture depletion. High temperatures, caused by both natural and human factors, led to greater evaporation and lower soil moisture, compounding the effects of low rainfall.

Nature of the drought

Meteorological

Prolonged below-average rainfall. The Murray-Darling basin especially experienced below-average rainfall from 1997-2009.

Increased average temperatures. The drought was accompanied, and exacerbated, by heatwaves. Lack of rain contributed to heatwaves.

Decreased humidity levels. The drought led to decreased humidity levels, leading to poor agricultural yields and faster drying of soil and vegetation.

Dry winds. Strong, dry, winds became more and more common due to the lack of vegetation. Led to the drying out of the landscape.

Hydrological

Decline in river flows. Major rivers, Murray-Darling basin, experienced significant reductions in water flow. Some almost dried up. Murray rover saw its lowest levels recorded in over a century.

Reduction of reservoir levels. Levels in reservoirs, especially those supplying Melbourne, Sydney and Adelaide, dropped drastically. Some dams reached critically low levels.

Decline in groundwater levels. Excessive extraction and reduced recharge led to a decline in groundwater supplies. This had an impact on isolated settlements reliant on wells and boreholes.

Lower river flows led to an increased concentration of pollutants in drinking water.

Agricultural

Failures and Reduction in crop Yields. Some farmers experienced crop failures, especially with water-intensive crops like cotton (already discussed). Wheat, barley, and other staple crops also had reduced yields in this period.

Livestock Losses and Production issues: Lack of water and pasture led to decreased livestock numbers. Many farmers were forced to cull animals or sell them prematurely, leading to a decline in meat and dairy production.

Soil Degradation and Loss of Land: Lack of moisture led to soil degradation, erosion, and loss of land. Over-farming in dry conditions also contributed to depleted soil nutrients, making recovery more difficult.

Increased Irrigation Costs: Irrigated farming became more expensive as water became scarce. Farmers had to abandon irrigation altogether or switch to less water-intensive crops.

Rural Employment Decline: Agricultural production issues led to a loss of jobs in farming communities, increasing rural unemployment and forcing some families to leave or sell their land.

Socio-economic

Water Restrictions and Rationing: Water restrictions were introduced in urban areas across Australia, including Melbourne, Sydney, and Adelaide. Households encouraged or required to conserve water, and public water use heavily regulated (e.g., limits on watering gardens or washing cars).

Rising Food Prices: Reduced agricultural production led to an increase in the cost of many food items, particularly dairy, grains, fruits, and vegetables. This put pressure on consumers.

Migration from Rural to Urban Areas: The economic hardship in farming communities, coupled with deteriorating living conditions, forced many to leave rural areas in search of work and better opportunities in urban centres. This further depopulated struggling rural towns.

Mental Health Issues: The drought had a psychological impact on farmers and rural communities. Many faced severe financial stress, and the prolonged nature of the drought led to an increase in depression, anxiety, and suicide among farmers.

Impact on HEP: Water shortages affected hydroelectric power generation, leading to concerns about energy security and rising electricity prices in certain regions.

Drought Relief and Intervention: The government had to implement large-scale drought relief packages to support affected farmers and rural communities. Billions of dollars were spent on subsidies, assistance programs, and water infrastructure improvements. These may have contributed to the easing of drought conditions in the late 2000s.

Impacts

Cotton production saw a 66% decrease during drought years compared to before the drought.

Melbourne saw rain 90% below average for 2006.

To offset the drought, in November 2006, Perth completed a desalination plant. This has since supplied 17% of the city’s needs.

Victoria invested in improving their mental health services to cancel-out the impacts of drought on farmers

The Sahel

What is it?

A band of land that sweeps across Northern Africa, covering parts of 11 nations.

A semi-arid region spanning much of Northern and Central Africa. It covers areas of 11 countries and is becoming more and more arid, and larger, over time.

Despite being semi-arid, since the 1960s there has been less and less rainfall and droughts have become increasingly severe. The most recent severe drought spanned 2011-2012

Causes of drought in the Sahel

- - - - Heat is transferred from the surface to the soil and then into the atmosphere
        
        This allows cooling to occur on the surface and therefore a low ground temperature.
        
        Is soil is cooler, there is less evaporation from the soil and thus more moisture.
      - The evapotranspiration from trees leads to the formation of clouds and thus leads to precipitation.
- - - - This means that there are no trees on the surface, meaning that solar rays hit the ground, increasing its surface temperature and cause moisture to leave the ground, drying out the soil. the Lack of evapotranspiration from trees means that there is less water cycling and, therefore, precipitation.
        
        40% of rainfall is caused by local evaporation.
        
        Due to poor practices in the Sahel, there is likely to be 40% less rain than they would be if it were a forested environment.

Physical causes

The MET found that an El Nino event can increase drought as it brings an easterly wind which can add to drying conditions. This particularly affects Western Sahel regions. A La Nina also seems to interrupt rainfall, as seen in 2011.

Human causes of drought

Research suggests that air pollution in Europe and North America changed the global heat budget and atmospheric circulation so tropical storms associated with the ITZC don’t arrive as the ITZC shifts to the south.

Poverty and low development rates mean that the population is growing significantly. (2.5%-4% birth rates per annum). There is a high demand for food, much of natural shrub/dryland is being over-cultivated.

Land grabbing of the most productive land results in an increase in water use and pushes local subsistence farmers out onto more marginal land, increasing the area of drylands being removed.

Over-grazing has recently become an issue as the population rises, reducing the amount of grazing land. This increases the head of cattle per square km leading to overgrazing and a loss of vegetation cover to hold moisture.

Human and physical causes of drought.

A study by NOAA believes that drought is due to higher sea-surface-temperatures caused by anthropogenic climate change, they found that rain bearing the winds of the Sahel fail if the sea surface temperature in the Atlantic are warmer than average.

The lack of energy sources means most people are using firewood as fuel. This reduces the recycling of water and vegetation cover which increases desertification and drought.