Definition of Desertification in the UNCCD

The term ‘desertification’ was employed in 1949 by the French forester Aubreville, who used the term to refer to the displacement of tropical rainforest by secondary savannah and scrub in those parts of Africa where forest was being cleared and burned to provide land for cultivation (WMO-UNEP, 1996). Auberville concluded that the process was especially active in the sub-humid tropics of Africa and was akin to the creation of deserts in the formerly forested areas.

 

The extent of accelerated soil erosion induced by indiscriminate felling and burning of forest and woodland in Africa and changes in the soil-water budget and hydrological cycle were understood as some of the factors leading to land degradation.

 

There was also a growing recognition of the part played by human activities and climate changes such as prolonged or frequent droughts aggravating land degradation. This led to formally defining desertification as “land degradation in arid, semi-arid, and dry sub-humid areas resulting from various factors, including climatic variations and human activities” (UNCED, 1992), which is used as the basis of the UNCCD.

 

Aridity of a region is categorised by the ratio of P = Mean Annual Precipitation to PE = Mean Annual Potential Evapotranspiration, using modified Thornthwaite formula. As per this, the aridity zones are classified as given in Table:1

 

Table 1. Classification of the Regions on the basis of aridity index

 

 

Climate Zone	P/PE ratio	% of world covered
Hyper-arid	<0.05	7.5
Arid	0.05-0.20	12.5
Semi-arid	0.21-0.50	17.5
Dry sub-humid	0.51-0.65	9.9
Humid	> 0.65	39.2
Cold	> 0.65	13.6
Source of Inf.: WMO-UNEP Report (1996): Interactions of Desertification and Climate

 

 

According to terminology accepted by CCD, “Land degradation” means reduction or loss, in arid, semi arid and dry sub-humid areas, of the biological or economic productivity and complexity of rainfed cropland, irrigated cropland, or range, pasture, forest and woodlands resulting from land uses or from a process or combination of processes, including processes arising from human activities and habitation patterns, such as:

 

(i) soil erosion caused by wind and or water;
(ii) deterioration of the physical, chemical and biological or economic properties of soil; and
(iii) long-term loss of natural vegetation.

 

Further the CCD defines “arid, semi-arid and dry sub-humid areas” as areas, other than polar and sub polar regions, in which the ratio of annual precipitation to potential evapotranspiration falls within the range of 0.05 to 0.65.

 

Degradation of land involves the reduction of the renewable resource potential by one or a combination of processes acting upon the land. The resource potential relates to agricultural suitability (rainfed or irrigated arable cropping, animal husbandry, forestry, inland fishery), primary productivity level, and natural biotic functions. More recent data on the extent of land degradation estimates that about 5 million hectares, or 33 percent, of total land acreage in Bangladesh falls below the minimum threshold for sustainable cultivation. In drier parts of Bangladesh low soil fertility is recognized to be at the root of the land degradation spiral:

 

low fertility -> low water use efficiency -> low biomass production -> decline in biological activity -> low availability of energy& materials -> poor soil cover -> run off -> soil erosion -> land degradation -> drought -> desertification

 

 

The land degradation spiral

 

Deforestation leads to increased water erosion with an indirect impact on water resource development, depletion of soil fertility, disappearance of many plant and animal species, local aridification, etc. In addition, flooding, accelerated runoff, droughts, more sedimentation in rivers and reservoirs and depleted groundwater become more severe because of deforestation, with adverse consequences for agricultural production and human life.

 

Other Definitions in the CCD

 

“Land” means the terrestrial bio-productive system that comprises soil, vegetation, other biota, and the ecological and hydrological processes that operate within the system.

 

“Land degradation” means reduction or loss in arid, semi-arid and dry sub-humid areas of the biological or economic productivity and complexity of rainfed cropland, irrigated cropland, or range, pasture, forest and woodlands resulting from landuses or from a process or combination of processes, including processes arising from human activities and habitation patterns such as:

(i) soil erosion caused by wind and/or water;
(ii) deterioration of the physical, chemical and biological or economic properties of the soil;
(iii) long-term loss of natural vegetation.

 

“Dryland” refers to the arid (excluding the polar and sub-polar regions), semi-arid and dry sub-humid areas in which the annual precipitation to potential evapotranspiration falls within the range from 0.05 to 0.65.

 

“Combating desertification” includes activities which are part of the integrated development of land in arid, semi-arid, and dry sub-humid areas for sustainable development which are aimed at:

(i) prevention and/or reduction of land degradation;
(ii) rehabilitation of partly degraded land; and
(iii) reclamation of desertified land.

 

“Drought” means the naturally occurring phenomenon that exists when precipitation has been significantly below normal recorded levels, causing serious hydrological imbalances that adversely affect land resource production systems.

 

 

The “drylands” are defined as those regions where the ratio of the mean annual precipitation to the mean annual evapotranspiration is in the range of 0.05-0.65. It is important to note that the CCD considers arid, semi-arid and dry sub-humid regions as dryland, but excludes the hyper-arid region, where the P/PE ratio is less than 0.05, from the ambit of the Convention. The Convention also excludes the moist sub-humid, humid and perhumid zones of various regions in the world.

 

The United Nations Environment Program (UNEP) estimates that the world will lose one-third of its arable lands through desertification by the end of the century. About 1 million hectares in Asia are subject to desertification. Most of the 82 to 92 per cent of this Asian soil resource affected by drought, mineral stress, shallow depth, excess water and permafrost is in south and southeast Asia. The countries suffering most from desertification are Bangladesh, China and India.

 

An estimated 2.6 million square kilometres of desert also occur in Australia, west Asia (Afghanistan, Islamic Republic of Iran, Pakistan) and other Asian countries. China's deserts are widely distributed throughout the northern districts and cover 13 per cent of its land area. Reportedly, China loses 120,000 hectares of farm and pasture land to drifting sand dunes each year.