Cause of Desertification

 

Desertification is land degradation in the drylands due to a number of factors including climatic variations and human activities. Man-made causes include, expansion of agriculture and unsustainable agricultural practices such as over cultivation, nutrient inputs, poor irrigation practices, deforestation and overgrazing. Such unsustainable resource management practices are often induced by population pressures, social conflicts and disruption of social systems, inappropriate government policies and poverty.

 

People affected by desertification often need to draw on their limited assets in order to survive, which accentuates their poverty. This constitutes a vicious cycle linking deteriorating natural resources to deteriorating livelihoods as people need to encroach further on fragile soils, sparse vegetation and limited water resources to meet their basis needs for food, shelter and livelihood. Many of the complex causal relationships are not fully understood. It is often very difficult to separate the causes from the effects.

 

(i) Unsustainable Agricultural practices

- Extensive and frequent cropping of agricultural areas.
- Excessive use of fertilisers.
- Shifting cultivation without allowing adequate period of recovery.

(2) Unsustainable Water Management

- Poor & Inefficient Irrigation Practices.
- Over abstraction of ground water, particularly in the coastal regions resulting in saline intrusion into aquifers.

(3) Conversion of land for other uses

- Prime forest into agricultural land.
- Agricultural land for other uses.
- Encroachment of cities and towns into agricultural land.

(4) Deforestation.

- Unsustainable forest management practices.
- Forest land clearances for agriculture (including shifting cultivation)
- Other land use changes (Projects- energy, roadways,etc).
- Overgrazing, excessive fuel wood collection.
- Uncontrolled logging and illegal felling and
- Forest fires.

(5) Industrial, mining and other activities without satisfactory measures for prevention of land
degradation and land rehabilitation.

(6) Demographic pressures - human and livestock.

(7) Frequent droughts/failure of monsoon and their link with global climate phenomena.

 

Unsustainable Agricultural Practices:
Unsustainable agricultural practices include excessive use of fertilisers, pesticides, frequent cropping patterns, inappropriate technologies, or choice of crops/ plants, etc. Non-point sources of pollution is a problem in areas with wide application of fertilisers.

 

Unsustainable Water Management Practices:

Poor & inefficient irrigation practices, over abstraction of ground water, particularly in the coastal regions resulting in saline intrusion into aquifers, etc. are some of major unsustainable water management practices which has led to problems of desertification in such regions. Overabstraction of groundwater without compensatory recharge has led to depletion of groundwater table.

 

Land Use changes. :

Diversion of land from forestry and agriculture to other land uses has been one of the principal causes of land degradation. Wherever diversion of forest land is unavoidable, for instance for developmental projects (energy, infrastructure, transportation, etc.) compensatory afforestation on non-forest land is mandatory. However, loss of prime forests could have an impact in the long-term stability of the forests.

 

The other land use change is due to encroachments, through violation of forest boundaries, illegal farming in forests. Due to their illegal status, they are unable to receive extension services and improve their farming systems, further accelerating land degradation. The encroachment of forest land, and the socioeconomic pressure to regularise them, continue to be the most pernicious problem of forest protection.

 

Deforestation:

It is difficult to separate the causes from the effects of deforestation and forest degradation. Some direct causes of deforestation are land clearances for agriculture (including shifting cultivation), other landuse changes including unplanned urbanisation, land transfers, different forms of encroachments, over-grazing, uncontrolled and wasteful logging, illegal felling, and excessive fuelwood collection.

 

Shifting Cultivation:

Shifting cultivation refers to a farming system in which a short but variable cultivation phase (on slash-and-burn land) alternates with a long and equally variable fallow period. With increasing pressure on forest lands, and shortening on the fallow period, this practice of farming which was once in balance with nature has become disorderly causing considerable damage to the regeneration of forests cleared in this manner. Deleterious effects include deforestation, spread of sterile grassland, soil erosion, and loss of productivity of forest and agricultural land.

Collection of Fuelwood:

Much of the rural energy for cooking comes from collection of fuelwood from forests. This contributes to the overall deterioration of the quality, stocking condition and productivity of the forest ultimately leading to deforestation and degradation.

Grazing in Forest Land:

Forest land are an important source of grazing and fodder in the absence of adequate pasture land and a viable policy of fodder development. These include traditional ethnic sedentary village livestock and migratory animals herded by ethnic grazers.

 

This results in overgrazing and over-extraction of green fodder, leading to forest degradation through damages to regeneration and compaction of soil.

 

Forest fires:

Forest fires, mostly ground fires affect annually huge of forest area. These are by and large incendiary in nature. The environmental impact of these depend on forest type. The nature and severity of damage depend on the type of forest, availability of fuel and climatic factors.

 

Industrial Activities:

Industrial effluents and mining are also gradually emerging as important agents of desertification. In most cases the root of the problem is the mismanagement by land users and poor implementation of pollution control regulations. Industrial effluents and their discharge into inland waters and irrigation with poor quality water in many parts of the country are rendering stretches of land in some of the areas as degraded. Industrial effluents from textile, printing and dyeing industry and their discharge into streams and rivers, which are non-perennial with no flow during the lean season severely contaminates them. Use of such waters for irrigation has affected agricultural land as well. Besides productivity decline or complete loss, progressive degeneration of bio-diversity is yet another major consequence of land degradation. In many areas the groundwater has been polluted.

Mining Activities:

Mining is another major industry, which is a factor of desertification in the country. This is especially with unplanned open cast mining and dumping of mine refuse in the vicinity of agricultural lands. Despite guidelines and regulations for undertaking adequate environmental measures mining operations, open cast mining of sandstone, limestone, marble, gypsum, and clay is largely practised by small scale entrepreneurs who do not take up post mining operations. Consequently, such areas are gradually turned into wastelands. China clay, Fuller’s earth, calcite and gypsum generate fine particles which are washed down the slopes with runoff and get deposited in the adjoining cultivated fields. This eventually leads to problems of waterlogging and salinity.

Disposal of Soild & Toxic Wastes onto Land:

In many parts of the country large tract of land have been rendered useless due to disposal of toxic industrial wastes. In some areas, this has led to ground water contamination as well. The costs for reclamation of such land, if carried out as per requirements, would be enormous.

 

Demographic pressures:

Population pressures is a significant factor for land degradation. Population Pressures in the Arid Region: The general problem of arid areas with large populations is essentially one of human ecology. The inherently limited resources within arid and semi-arid regions set the ultimate limit of production are finally dependent. Furthermore, erratic rainfall results in widely fluctuating production leading to scarcity, which imposes stress on these populations. In general, the population density of both human and livestock in the arid region is much higher than the national average.

As population increases, the demand on natural resources is further magnified. This has led to further intensive use of land and other natural resources in drier regions. The consequence is an imbalance between the human and animal population on the one hand and plants, water, and land resources on the other. As the demand by the first persists and increases, the resources tend to become depleted and, as depletion proceeds, the stress upon them becomes even greater. Thus, a process of progressive degradation of resources is set into operation, which intensifies with drought. If not checked timely and effectively, it leads to loss of vegetation, leading to loss of biodiversity. The barrenness of the land affects the hydrological cycle which can affect the rainfall pattern for the region. In the semi-arid, sub-humid regions of the country also, there are some areas such as the Gangetic Plains, where the population density is one of the highest in the world.

 

Drought and Land Degradation:

Drought is generally a naturally occurring phenomenon due to deficit of rainfall in a region. However, drought effects can be exacerbated due to absence of vegetative cover impacting the hydrological regime. Drought could thus be another causative factor for land degradation. Arid and semi-arid regions in the country encounter moderate to severe droughts frequently leading to crop failures and famines. While droughts of transient nature may not cause significant adverse effect on the crop and livestock production, severe droughts of recurring nature lead to lower biomass production, poor grain yields and scarcity of fodder. In areas with restricted growing season and soils of poor water holding capacity, droughts have a significant impact on the total biomass yield. Such situations result in minimal inputs of organic carbon into the soils. Even the biomass recycling through leaf litter from perennials is reduced.

 

Further more, scarcity during drought years leads to enhanced grazing pressure by the livestock which accentuates the problem of loss of vegetative cover. The process is aggravated if the following year also is a drought year. This way recurrent droughts lead to land degradation mainly through decline in biomass production and depletion of organic carbon (humus) in the soils. It is, therefore, not surprising that some of the most severely degraded land are found in the chronically drought prone areas having shallow and light textured soils.

 

Climatic Change and Bio Diversity

 

Climate change and desertification are independent phenomena, but in constant interaction. Climate gives the boundary conditions for the desertification progress, and desertification changes the partitioning of energy and water fluxes that affect the atmospheric circulation. Both of them are influenced in their evolution by human action. The recurrent cycles of climate heating in history seem to have been altered in the last century mainly by the consequences of human development. However, the sinergical interaction between climate change, ie global warming, and droughts could favour desertification.

 

This situation is reflected clearly in the northwestern and western parts of Bangladesh, where the incidence of droughts in the last few decades and overexploitation of the aquifers and the apparition of soil salinisation processes are common. The exhaustion or eutrophication of groundwater and the degradation of the ecosystems have also accompanied it. The fragile equilibrium that sustains the ecosystems of the dry lands is affected by these variations in climate. Moreover, diversion of Ganges water at a crucial point of the upper riparian country has caused a depletion of soil water in the rhizosphere of the soil profile. This poses a dangerous threat to the survival of many species of flora and fauna common to these areas and contributing much to the richness of bio-diversity in the country.

The IPCC reports that under some scenario of climatic change for late in the 21 st century, Bangladesh would remain a savanna/woodland. The availability of winter water will decrease, and irrigation will be more dependent on groundwater withdrawal. Under such a condition, it would be quite difficult to control salinity intrusion, to keep navigational routes functional, and to ensure environmental and ecological harmony in various places especially in the Ganges, Atrai and Teesta dependent areas of the country.

 

At present, western parts of Bangladesh are periodically being affected by droughts in winter. With temperature rise the winter precipitation might decrease further, and the moisture content of topsoil would decrease substantially leading to severe moisture stress. Rabi drought would severely affect wheat and Boro crops at vegetative growth stages. Increased drought will increase salinity build up in the topsoil. There is a need to develop drought-tolerant crop varieties and drought- mitigation technologies that will make maximum use of the land resources, of the rain fed farming system and the limited rainfall in the region. Complementary concerns include appropriate water storage and rainwater harvesting technologies, supported with packages of agronomic practices to increase productivity of the Kharif crops and vegetables.

 

Withdrawl of Water

The hydrological and climatic conditions of Bangladesh are characterised by too much water in the wet monsoon and too little in the dry months. The drought environment is further aggravated by the cross boundary anthropogenic interventions. About 58 rivers that flow through Bangladesh actually come through India and Myanmar (India 55 and Myanmar 3). Most of these trans-boundary rivers enter into the country along the NW and SW regions.

 

The natural flow of these rivers is interrupted by upstream withdrawal of water for economic and household uses as well as for construction of water management structures by the concerns countries. The effect on these structures obstructs the normal flow of water in rivers such as the ganges at (Farakka), the punarbhaba (just beyond Banglabandha) and the tista. These structures mostly divert dry season flow of the rivers, which create not only a scarcity of surface water in NW and SW Bangladesh, but also tend to affect negatively the recharge of groundwater in these regions. Ultimately it leads to moisture loss in a vast area and contributes to drought condition in these two regions of the country.

 

Groundwater hydraulic resource beneath the surface of the ground, consisting largely of surface water seeped down. Such water accumulates in porous strata and soils. Groundwater represents around 30% of freshwater resources of the earth, while lakes and rivers correspond to less than 1%. The largest volume of freshwater is stored in glaciers (69%). Groundwater is one of the components of the hydrological cycle, stored underground in rock layers called aquifers - it is a result of infiltration of rainfall and surface water with which it maintains a close relationship. When this water reaches the groundwater table (ie the groundwater's upper level), it begins a long, slow journey underground, moving at rates ranging from a few millimetres to a few meters per day.

 

Groundwater in Bangladesh occurs at a very shallow depth where the recent river-borne sediments form prolific aquifers in the floodplains. In the higher terraces, the Barind and Madhupur tracts, the Pleistocene Dupi Tila sands act as aquifers. In the hilly areas, the Pliocene Tipam sands serve as aquifers. The groundwater table over most of Bangladesh lies very close to the surface and fluctuates with the annual recharge discharge conditions. Recharge to aquifers in Bangladesh is mainly from vertical percolation of rainwater and floodwater. Rivers and other standing water bodies provide local recharge to the nearby aquifers. The main component of discharge is the withdrawal of groundwater by different types of tubewells. A minor component of discharge is natural flow towards lower gradient. The groundwater level is at or very close to the surface during the monsoon whereas it is at maximum depth during the months of April and May. This trend is common over most of Bangladesh except Dhaka City and the barind tract. Because of uneven distribution of water resources, dry season demand for water in Bangladesh is mainly met by groundwater.

 

Presently about 80% of the people in rural Bangladesh depend on groundwater for drinking. Urban water supply is also largely dependent on groundwater. In Dhaka City more than 95% of the supply comes from groundwater and the remainder is provided by treated surface water. Groundwater also contributes largely to irrigation and under 1995 conditions 72% of the total coverage was provided by groundwater. The Master Plan Organisation (MPO) in 1989 estimated a reserve of 25,750 million-meter cube (MMC) of groundwater in Bangladesh. Of this 1,686 MMC is unavailable and 900 MMC remains in reserve for domestic cum industrial use, and a maximum of 12,809 MMC is available for agriculture.

 

The most serious constraint is the largescale arsenic contamination of groundwater. Before the discovery of arsenic contamination 97% of the rural people used to rely on groundwater. Now the coverage has come down to 80%. Apart from arsenic the other quality issues include high concentration of iron, high salinity in coastal areas, high concentration of manganese etc. Faecal colliform is also a problem, particularly for shallow groundwater. Decline in groundwater level in the dry season due to larger withdrawal for irrigation is another constraint for water abstraction by certain technologies. Most commonly used hand tubewells cannot pump water if the level goes below 6m. For large production wells like the wells in Dhaka city, continuous lowering of water level means higher and higher production cost. Ground subsidence is another adverse impact of lowering groundwater level. Although predicted, there is no sign of land subsidence due to groundwater withdrawal in Bangladesh. Indiscriminate disposal of industrial and municipal wastes in large cities cause groundwater quality degradation as seen in Dhaka city.

The River-linking Programme in India
(Inter Basin Water Transfer Link Project of India)