Excessive irrigation promotes desertification (Google / The New Nation)

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Excessive irrigation promotes desertification

Sharmia Sultana

Desertification, decline in the biological or economic productivity of the soil in arid and semiarid areas resulting from various factors, including human activities and variations in climate is going ahead with an reeducated pace. Desertification refers to the formation and expansion of degraded soil, not to the advancing movement of the current deserts. Desertification is found on every continent except Antarctica.  Poor land management, such as overgrazing and over cultivation of dry lands, can easily lead to land degradation and desertification. Increasing population and improper irrigation techniques also contribute to desertification.

Desertification occurs in cropland (both irrigated and nor irrigated), pasture, and woodlands. Loss of soil, deterioration of soil, and loss of natural vegetation lead to desertification. Drought, a period of unusually dry weather, can cause loss of vegetation, which in turn leads to desertification. Poor land management and increasing population are factors that promote increased irrigation, improper cultivation or over cultivation, and increased numbers of livestock. These events alter the land and the soil, diminish the resources, and increase the chances of desertification.

Desertification has sometimes been mistakenly described as the expansion of deserts into nondesert areas. Pictures of sand dunes engulfing agricultural lands encourage this misconception, but this type of desertification is rare. Arid and semiarid lands can be degraded even if there is no adjacent desert. Drought has also mistakenly been called the primary cause of desertification. Desertification can occur without drought, and drought can occur without resulting in desertification. Droughts are short-term and cyclical. By themselves, they do not degrade the land. However, they intensify the pressures that lead to mismanagement of land, plant, and water resources.

While dry land rainfall is low on average, it is extremely variable from year to year and from place to place. Native plants and animals have adapted to this variability. For example, the seeds of many desert plants can remain dormant through several years of drought, waiting for a good rain to sprout. In order to survive in this harsh environment, humans must adapt their activities as well. However, many factors, including population growth, poverty, politics, disrupted social institution and the pursuit of short-term economic opportunity, may work together to promote unsustainable practices.

Ironically, the availability of water for irrigation can cause desertification. Nearly all irrigation water contains some salt. If an irrigation system lacks a good drainage system, then the salt accumulates in the soil. Eventually, the salt reaches levels toxic to most plants. This problem is now jeopardising about one-third of the world’s irrigated land.

In most cases of desertification, there is a reduction in total species richness, an increase in the proportion of exotic (nonnative) plants, and a decline in overall biodiversity-the variety of life forms and the ecological roles they fill. Once desertification starts, it often causes changes that accelerate the process. For example, desertification often results in a decrease in the amount of vegetation covering the land. With less vegetation providing shade, soil temperatures rise, accelerating the breakdown of organic matter in the soil and the evaporation of water. Some soils may become compacted or crusted, reducing their ability to absorb the limited rainfall that occurs, which further reduces the amount of water available for plants.

The absence of vegetation also enhances runoff and erosion by water and wind. Erosion may form deep gullies, lowering the local water table (level of water within the ground) and making less water available for plants.

Wind erosion blows away nutrients in the soil and may physically damage plants. Each of these effects makes plant growth more difficult and may further reduce the amount of vegetation covering the land, which in turn leads to more degradation.

For land managers, desertification is a downward spiral. As it proceeds, the impact of any down turn such as a drought may become catastrophic and result in loss of human lives due to lack of necessary resources, such as water. With diminishing productivity any profitability comes increased pressure to compensate for declines. Livestock grazers increase herd sizes, and farmers plant all available lots of land and continue to irrigate even though yields poorest regions where no other employment is available, rural populations turn to woodcutting and charcoal production, which lead to deforestation. This deforestation forces families to spend more time seeking firewood for domestic use, leaving less time for tending fields or animals.

Desertification has become a large-scale problem. Arid and semiarid regions, known as dry lands, account for one third of the world’s land area and support a combined population of about 900 million people. Soil degradation reduces crop output and is a major concern economically.

About 70 percent of dry lands are susceptible to degradation, 50 percent have been degraded to some degree, and 15 percent show extreme degradation where agricultural yields are less than half of their former level. Almost all the areas of extreme degradation are in the African Sahel from Senegal to Sudan, along the Mediterranean from Tunisia to Egypt, and in central and southwestern Asia from China to Syria.

Desertification can also have impacts that extend beyond the immediate degraded area. Wind-borne dust from the Sahel creates havoc with air traffic across western Africa, and sediment eroded from central China damages water control systems far downstream. Many regions are affected indirectly by desertification as they absorb waves of people uprooted by their inability to grow enough food or raise enough livestock.

Such people, called environmental refugees, swelled the urban areas of the Sahel during the 1970s and 1980s. Moreover, migrations of environmental refugees may cross national boundaries and contribute to political friction within and between countries. This migration problem has occurred at various times, such as during the drought years from 1968 to 1973 when Mauritanian nomads fled into Senegal.

Most efforts to combat desertification require temporary reductions in economic productivity or increases in investment. Experts commonly recommend decreasing herd sizes, changing plowing practices, planting windbreaks, planting less profitable crops, and allowing each field to lie fallow on a rotating basis. In irrigated agriculture, more expensive and intensive water management is recommended, requiring improved water delivery systems, field preparation, and drainage systems. Increasingly poor populations, however, cannot absorb a reduction in income, cannot usually invest in improvements, and may not have sufficient labour available to implement even simple measures.

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