2.4 Desertification
what is the scale of desertification?
land covering 12 million hectares is lost every year. it affects everyone due to soil exhaustion reducing the worlds food production. 110 countries are affected by desertification. Annual land lost could produce 20 million tonnes of grain through desertification. It is not irreversible
what are the current causes of desertification?
natural climate variability in the inter-tropical convergent zone anthropogenic climate change overgrazing over cultivation including poor irrigation systems deforestation
what is the predicted climate change and its impacts?
temperature will rise (temperature increase will be greater on land than over oceans and greater at higher latitudes than in the tropics and mid-latitudes) changing precipitation (warmer average temp will cause a higher rate of evaporation) changing severe weather (warm ocean surface waters provide the energy that drives intense storms) more clouds (warmer global temps produce faster overall evaporation rates, resulting in more water vapour in the atmosphere and then more clouds)
are high HDI countries at risk of desertification?
there is a big link between desertification and hunger and poverty. More than 110 countries have drylands potentially at risk. However, it does affect HDI as well as LIC because deforestation results in a decline in food production and the annual income forgone in areas immediately affected by desertification amounts to approximately US$42 billion each year.
what are the physical causes of desertification?
1.climatic factors (e.g. global warming) 2.decrease in the amount of rainfall (make land more vulnerable to desertification) 3.high temperatures (drying up water resources and to droughts)
what is the definition of sustainable?
development that meets the needs of the present without compromising the ability of future generations to meet their own
What percentage of the Earth's surface is currently at risk from desertification?
- A third of the land worldwide is at risk from desertification - Worst affected areas are Africa, Asia and latin America (all middle and low HDI countries) - 46% of Africa is at risk of desertification and 25% is at high or very high risk - 110 countries have regions that are threatened -Countries most likely to be affected by future desertification are areas in the around the tropics of cancer and Capricorn (especially north of these areas) have a high risk of desertification. The most impacted continents Africa and Asia where countries such as Zambia and Zimbabwe and the sub-Himalayan Indian and north eastern china are at high risk of desertification.
how can desertification be caused by salinisation? (human cause)
- Desertification can be caused by salinization - This process is triggered by deforestation and/or excessive irrigation which causes an increase in the water table - The rising water contains soluble soils and as the water evaporates, the soils are left on or near the soil surface - Plants struggle to grow in saline conditions resulting in land degradation
what are the priorities of the effective management of desertification in the future?
-global orchestration (ecosystem management is reactive to current issues) -techno garden (technology sharing to allow places affected by future desertification to be proactive in prevention by using green technologies) -adapting mosaic (empowering the development of local adaptations and learning) -order from strength (places are empowered to reach to environmental problems as the development)
how does natural climate variability in the inter-tropical convergence zone cause desertification? (physical)
A physical factor causing desertification is the natural climate variability in the Inter-Tropical Convergence Zone (ITCZ). The Intertropical Convergence Zone (ITCZ) is a band of low air pressure (cloud and rainfall) that moves across the tropics creating wet seasons and dry seasons in the sub-tropical drylands, for example the Mojave Desert receives up to 150 mm of rainfall in winter and up to 50 mm during the summer months.There are natural long-term changes in the movement of the ITCZ and when it delays to arrive, this causes prolonged drought in dryland areas. During periods of drought, there is a decline in vegetation cover and increased wind erosion, therefore causing dryland degradation and desertification. This cause of desertification is a particular risk to lower HDI countries, as they tend to be located in the sub-tropical climate zone. This is not considered to be a very important cause of desertification because in some years, the natural variability means that the ITCZ will prolong causing increased rainfall and ecosystem recovery.
how does anthropogenic climate change cause desertification? (human caused climate change)
Caused by human activities like burning fossil fuels, which releases greenhouse gases into the atmosphere, and deforestation, which reduces the amount of CO2 which can be stored in vegetation, as well as releasing greenhouse gas emissions and causing soil erosion.Human activity puts 6 million tons of carbon dioxide into the atmosphere each year- this is one tonne for each person on the planet. Desertification and drought affect approximately 1 billion people and 25% of the earth's total land surface. 70% of the 5.2 billion hectares used for agriculture around the world are already degraded. In Nigeria, overgrazing and over-cultivating are converting 351,000 hectares of land into the desert each year.
what is the top-down solution?
Denoting a system of government or management in which actions and policies are initiated at the highest level. This approach tends to centralise decision making, usually the government and other external groups, and is often linked to development through large scale projects.
what is agreed about the risk and causes of desertification in the future?
Desertification have major feedback loops so has no single cause or a single simple solution. The least developed countries will be most affected by desertification as low levels of HDI will exacerbate and be exacerbated by the impacts of desertification (especially places with the most pressing population pressures). However, the pattern and rates of desertification are very varied, and this suggests that other global level solutions to climate change, problems posed by desertification are going to be found as grassroots levels by the local populations at risk. desertification is a positive feedback cycle, which amplifies desertification.
what is globalisation?
Globalisation is the process by which national economies, societies and cultures have become increasingly integrated through the global network of trade, communication, transportation and immigration.
what is the impact of desertification on ecosystems?
Habitat ranges= species pushed to higher altitudes and latitudes, reduction in habitats, increased competition between species. Tipping points= reached more quickly, irreversible change occurs quicker than expected Extinction risks= some species will thrive but many more will become extinct Animal and plant life cycles including=migration, mating, seed setting and fertilisation Food webs= just one species removed from a food chain affects all others in that web Changing distribution of pathogens, parasites and diseases, affecting= human health, agriculture and fisheries
what approaches to ecosystem management are least effective to reduce the risk of desertification?
In a fragmented regionalised world, the role of global organisations will be limited and there could be reduced interest in the exchange of technology and resources, and in issues beyond national borders. As poverty and unsustainable land use will continue to be the main causes of desertification this should lead to global officials concentrating on getting them proactive to reduce the risk of desertification to reduce future risk.
How does over-cultivation cause desertification? (human)
Over cultivation is a purely an anthropogenic process and can cause lots of erosion and degradation. This happens as the machinery and intense farming can cause the soil to become weak and thin as it is constantly eroded. Combined with intense rainstorms this weak soil is often stripped off and transported away leaving a very low nutrient soil which plants struggle to grow in. Furthermore poor irrigation schemes can cause significant damage. For example in the Touat region of Southern Algeria, the use of modern powerful water pumps which removes large quantities of water from groundwater stores causes massive loss of water. This Irrigation scheme leads to 50% of water being evaporated in an area that only receives 50mm of rainfall a year. This is then a catalyst for more degradation as agriculture intensifies in order to counter declining yields. Despite this, there are some successful irrigation schemes that can store more water which has positive effects rather than negative. In lots of the potential desert locations the land tends to be more cultivated than grazed and therefore it is more responsible for desertification.
how does overgrazing cause desertification? (human)
Overgrazing is a human activity which causes soil to lose the ability to support plant growth, to hold moisture and it strips the soil of any vegetation cover. Farmers harvest their crops, stripping the field of the vegetation and then compact the soil with cattle leading to an infertile soil. This is a leading factor in desertification as it leads to an arid area where soil is low in organic matter, which is the result of no vegetation cover. This can be seen in Nigeria where overgrazing and over-cultivating has converted 351,000 hectares of grassland and cropland into desert each year. Overgrazing happens worldwide in both high and low HDI, but it is more common in low HDI countries due to the lack of technology and knowledge. Overgrazing increases as the rising population causes more demand for cattle and therefore more land is being overgrazed to compensate for the demand. In Eritrea, the Government has tried to reduce overgrazing by passing a law to distribute land to villagers who get usufruct rights to a piece of land for their lifetime. Traditional knowledge of the area also helps to effectively reduce overgrazing, in Mongolia tribes kept large herds of goat, sheep and horses so to preserve the soil and grass they would rotate the grazing areas, but only 20% of the population is from the original tribes now. With high demands for cattle and little knowledge of soil more areas are becoming arid areas, making overgrazing a leading factor to desertification.
how does deforestation cause desertification? (human)
Populations cut down trees for fuel/building material, leading to the removal of vegetation cover and causing soil to be exposed to water/wind erosion so it becomes shallow, infertile and dry. For example, Sudan has a deforestation rate of 2% per year, and in areas surrounding the Nile, dense forest has turned to infertile sand flats over the years, causing huge problems for local biodiversity and village subsistence farming. Another issue is vegetation cannot re-establish on the degraded soil, worsening the problem as people are forced to remove further forest cover and farm in more marginal areas (amplifying the effect of overcultivation on desertification). For this reason, the effects of deforestation are likely to increase in the future, making it a significant contributor to desertification over time. This issue generally affects less developed countries, where the population rely on wood for fuel/building and have little choice for affordable alternatives. However, this cause of desertification is reversible, with existing reforestation/afforestation projects having created forest-sustaining land from infertile desert. A significant example is the 9 mile wide "Great Green Wall" project stretching across the North of Africa. The new tree cover helps to stabilise soil, retain moisture and slow overland flow - reducing fluvial erosion on the soil. So although deforestation is a major factor in desertification, it is reversible so perhaps is not the most significant contributor.
what approaches to ecosystem management are effective to reduce the risk of desertification?
Proactive approaches are likely to be more effective in addressing economic problems and desertification (technogarden and adapting mosaic). Local populations need to be helped to adapt to current and future pressures to reduce current and future vulnerability and improve their resilience.
what is the bottom-up solution?
Projects that are planned and controlled by local communities to help their local periphery area. They are not expensive because they are smaller, more appropriate technology, which the local people will have to pay for.
what is the impact of desertification on the landscape?
Reduced soil fertility= crop and livestock yields decreased, crop diversity decreases Soil erosion= sedimentation of water courses increases likelihood and intensity of floods Dust storms= increased discomfort and eye diseases Breakdown of society= young and economically active may leave to find work elsewhere Drought and famine= malnutrition and starvation 'forced' migration= increased pressure on neighbouring areas, conflict due to increased pressure on remaining land Loss of land=loss of homes and possessions, cultural ties to place are broken Loss of culture=traditional customs and ways of life are lost
what is regionalisation?
Regionalisation is dividing an area into smaller segments called regions. This can be used in countries through dividing states but also businesses use this as a management tool. This is how geographers identify the parameters of regions within a greater area of space
what is the impact of desertification on populations?
Soil erosion and loss of topsoil, increased amounts of sand and dunes, increased areas of treeless zones, increased sedimentation of surrounding rivers and lakes= existing landscape encroached upon Increasing salinity of soils, increased numbers of sandstorms, vegetation damaged by sandblasting from desert winds= development of salt crusts
which is soil important (human impact of desertification)?
Soil is a hot bed of living organisms; it feeds us, and we all depend on it. It covers the earth but even though it is only a couple of cm thick, it is home to an extremely rich ecosystem, and they convert this matter for nutrients for plant growth. It takes 500 years for 2.5cm to form but only a few years to be broken- this is desertification.
how has the distribution of hot desert changed over the last 10,000 years?
The greatest amount of extreme deserts presently is found linear across 31% of Africa (the Sahara) however this has not always been the case as in the early Holocene 8,000 years ago there was only one area of extreme desert in Africa and the only concentration of extreme deserts where found in western Asia and south America. Since the last glacial maximum there has been a very significant decrease in the extent of extreme deserts. From being widespread across all continents, to almost no extreme desert. There has been a moderate increase in the extent of extreme desert. From almost no extreme desert across the globe to some in north Africa and central Asia. Presently, there is an intermediate amount of desert environments with the largest extent in northern Africa and the smallest extent in central Asia however with increasing climatic temperatures and sporadic rainfall, the distribution of the worlds desert is likely to expand over considerably larger areas.
what is the evidence for climate change in the last 20th century?
The intergovernmental panel on climate change states that areas like the Sahel are experiencing less and more unpredictable rainfall (in the last 25 years the Sahel had the greatest loss of rainfall anywhere on the planet) and a lot higher temperatures and a reduced water supply as rivers dry up and the water table falls. From the last quarter of the twentieth century and the start of the twentieth century the earth has experienced significant climate change with unprecedented enhanced rates of global warming. Some sources suggest the average temp of the planet rose between 0.3-0.6 during the last century.
what is uncertain about desertification in the future?
The millennium ecosystem assessment commissioned by the UN in 2005 said that looking to the future is difficult and combating desertification will depend on the development path the world follows. The four scenarios that they suggested saw 2 with a world of increasing globalisation and two with increasing regionalisation and both opportunities saw both top-down and bottom-up
what was the last glacial maximum?
The most recent interval in earth's history when global ice sheets reached their maximum integrated volume. The last glacial maximum was 18,000 years ago
what is desertification?
The persistent degradation of dryland ecosystems by human activities and by climate change. It is an example of a positive feedback loop
what are grassroots?
These are the most basic level or an activity or organisation. They are community-based approaches created to address localised problems.
what was the holocene climate optimum?
This was 8,000 years ago where temperatures where much warmer (similar temperatures to today) but the extent of deserts is confined to very small areas, with present day deserts extending over considerably larger areas. This climatic event was caused from predictable changes in the earth's orbit and this caused the end of the last glacial period.
what are the human causes of desrtification?
Today, a third of emerged land is threatened by degradation. The use of chemical fertilisers weakens the living organisms responsible for soil fertility. Regular ploughing dries out and compacts soil. Deforestation and overgrazing strips soil of the vegetation cover that protects it from erosion and this leads soil to be dried out and is carried away by wind and rain. Irrigation systems increases soil salinity and makes it infertile. Poverty is often a root, indirect cause and the process increases poverty However, it can also occur in high income countries due to intensive farming, irrigation and salinization
What are the 3 pillars of sustainability?
environment, economy, society
