Chapter 5 - Status of degradation. II. Other types of degradation and summary

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Waterlogging
Salinization
Lowering of the water table
Other types of degradation
Watershed degradation and management
Summary: the severity and extent of land degradation
Discussion

Waterlogging

(Tables 11 and 12, Figure 6)

Waterlogging is the rise of the water table into the root zone of the soil profile, such that plant growth is adversely affected by deficiency of oxygen. The critical depth depends on the kind of crop, but waterlogging is commonly defined as light for a soil profile depth of 3 m for substantial parts of the year, and moderate for less than 1.5 m. The severe degree occurs with a water table at 0-30 cm depth, and also included in this study is ponding, where it rises above the surface.

Waterlogging as a form of land degradation should be distinguished from naturally occurring poorly drained areas, and also from the different problem of flooding, which is noted below.

In the GLASOD estimate, waterlogging affects 4.6 M ha, largely in the irrigated areas of India and Pakistan. It is closely linked with salinization. In Iran it occurs in the coastal zone. The progressive rise in the water table beneath the Indo-Gangetic plains since the commencement of large scale irrigation schemes in the 1930s has been monitored (e. g. Ahmad and Kutcher, 1992).

TABLE 11 - GLASOD assessment: areas affected by waterlogging (Unit: 1000 ha)

TABLE 12A - Country estimates of areas affected by waterlogging

TABLE 12B - Revised estimates of areas affected by waterlogging

Figure 6 - Waterlogging, salinity and lowering of the water table: GLASOD assessment

Country estimates are given in Table 12A. For India, the figure given is more than twice the GLASOD estimate. For Pakistan, four sources quoted give total areas affected of 3.7, 1.6, 2.1 and 2.1 M ha, compared with the GLASOD value of 0.96 M ha. Since the Pakistan country data come from at least two independent surveys, show good agreement (relative to the standards found for other types of degradation!) and are believed to result from detailed field surveys, the country estimates are preferred.

For the purpose of subsequent discussion, the GLASOD estimates of areas affected by waterlogging are accepted for all countries except Pakistan, for which they are modified as in Table 12B.

Salinization

(Tables 13 and 14, Figures 6 and 7)

The generalized term salinization is employed here to cover all changes to soils involving the increase of salt, including both salinization in the narrow sense, the increase of free salts, and codification, the saturation of the exchange complex with sodium. The following definitions are in common use:

ECe = electrical conductivity of the saturation extract
ESP = exchangeable sodium percentage

Note: limiting values of ECe 4mS/cm and pH 8.5 were formerly used.

In the GLASOD estimate, the region is estimated to have 42 M ha affected by salinization, nearly all in the dry zone. Of this, 33 M ha are in Iran, where more than half of all agricultural land is shown as being affected. There are approximately 4 M ha in both India and Pakistan. In relation to irrigated land, the percentage affected appears as 10% for India, 23% for Pakistan and 9% for Sri Lanka, although these values should be reduced since some of the salinization results from saline intrusion into unirrigated land.

The values for strong salinization are important, for this by definition refers to land abandoned from cultivation. The area affected is 10 M ha of which 8 M ha are in Iran and 2 M ha in India. The absence of strong salinization from areas of Pakistan under similar irrigation and land management systems to those of India suggests a reporting bias.

The map shows a clear localization in two situations, irrigated land and coastal zones. A dry coastal strip along much of Iran through Pakistan to Gujarat in India is affected, in part by saline intrusion. The other areas heavily affected are the Central basin areas of Iran and the irrigation systems of the Indo-Gangetic plains.

TABLE 13 - GLASOD assessment: areas affected by salinization (Unit: 1000 ha)

TABLE 14A - Country estimates of areas affected by salinization

NA: Not assessed.
* For India, a further estimate of 6Mha is given by Sehgal and Abrol (1992).

TABLE 14B - Estimates of areas affected by salinization, Pakistan

Figure 7 - Salinization severity (GLASOD estimate)

TABLE 14C - Revised estimates of areas affected by salinization

Despite the existence of relatively clear definitions of salinity, country estimates show wide ranges of values (Table 14A and 14B). It should be noted that some of these include naturally occurring saline soils. For India all are higher than the GLASOD value of 4 M ha, ranging between 7 and 26 M ha. For Pakistan, there is better agreement; leaving aside three estimates of 9-16 M ha, the GLASOD and six country estimates lie in the range 4-8 M ha. Two apparently independent surveys, by the Soil Survey of Pakistan and the Water and Power Development Authority, show relative agreement at 5.3 and 4.2 M ha respectively.

Some of the large areas mapped for Iran consist in part of soils may have been naturally saline to some degree. Some also became salinized at earlier periods, before the modem era; there are records of people living in areas which are now unpopulated due to saline soils (A. Farshad, persona! communication). Since the present report is concerned with the modem era, the GLASOD estimate of area of salinization has been reduced.

In Bangladesh, an extension inland of coastal soil salinity has been noted in recent years, where the reduced river flows, consequent upon irrigation, is not sufficient to dilute and displace sea water. In Sri Lanka, small areas of light salinization have appeared on irrigated lands of the Mahaweli scheme; the problem has not yet reached serious proportions, but should be monitored.

Estimates of the extent of saline soils need to be associated with the dates of survey. Through successful reclamation, the extent of saline soils has been reduced in some areas, particularly as a consequence of the series of Salinity Control and Reclamation Projects (SCARP) in Pakistan. For example in the Pakistan Punjab the area of waterlogged and saline soils, which had risen from 61 000 ha in 1960 to 68 000 in 1966, had been reduced to 23 000 ha by 1985 (Chopra, 1989).

On the basis of this information, the GLASOD estimates for India, Iran and Pakistan are revised as in Table 14C.

Lowering of the water table

(Table 15, Figure 6)

In areas of deep alluvial deposits and where the groundwater has not become saline, tubewell irrigation has become widespread, and has led to substantial increases in crop production. Its very success has, however, led to over-extraction of water, in excess of the rates of recharge. A consequence is that the groundwater table has been progressively lowered.

TABLE 15 - GLASOD assessment: areas affected by lowering of the groundwater table (Unit: 1000 ha)

In the GLASOD estimate, nearly all of the 20 M ha reported are in Iran, where there is much irrigation from wells and abstraction beyond the capacity for recharge is widespread. An area of 0.1 M ha is reported for Pakistan. The absence of a reported area for India suggests that lowering of the water table was not recognized by the responding organization as a form of "land" degradation.

This form of degradation has certainly occurred in India. In parts of the Punjab, the water table has fallen by between 0.5 and 4.0 m in the eight year period 1978-86, and is receding at 0.3-0.5 m per year (Singh, 1992). In the Sudhar block of Ludhiana district, it has fallen between 1965 and 1989 from 3 m to 11 m, and in Haryana between 1974 and 1989 from 4.8 m to 7.7 m (Joshi and Tyagi, 1991).

Data on the extent of such lowering in India have not been identified, and the definitions of degrees of severity are not fully applicable to this type of degradation. However, on the basis of these reports, nominal additions to the GLASOD estimates of 100 000 ha light and 100 000 ha moderate degradation are made.

Other types of degradation

Deforestation and forest degradation

Deforestation is a widespread and serious type of land degradation in the region. At the same time, it is a major cause of other types of degradation, particularly water and wind erosion.

The extent of forest cover in 1980 and 1990, and the annual rate of deforestation, is the subject of a current FAO project, Forest resources assessment 1990. As the most reliable recent estimate, the data given by this project are adopted in the present study. It should be noted, however, that like the estirnates for other forms of degradation, these data are by no means fully agreed. Other estimates exist both for total forest area and rate of deforestation, which differ by as much as 50% in some cases.

TABLE 16 - Estimates of forest are and rate of deforestation

Data for Afghanistan and Iran are not currently available.
Source: FAO forest resources assessment 1990 project.

The FAO data are shown in Table 16. In absolute terms, the annual rate of deforestation has been highest for India, at 339 000 ha per year, whilst clearance rates of over 50 000 ha per year occur in Nepal and Pakistan. Even the small country of Bhutan has been losing 16 000 ha of forest each year. In instances these clearances are reducing what are already very small total forest areas, under 6% of the country for Bangladesh and under 3 percent for Pakistan. Both these countries are losing 3% of their small remaining forest areas annually.

Quantitative data from the FAO assessment are not currently available for Afghanistan and Iran, but rates of deforestation there are known to be high. Further information on deforestation for countries of the region is given in ESCAP (1986).

A related form of land degradation is forest degradation, the reduction of the standing biomass and, in extreme cases, potential for regrowth of areas which still remain as forest or woodland (Banerjee and Grimes, in press). Forest degradation results from the cutting of woody formations in excess of their capacity for regrowth. Most involve cutting of natural forests, but illegal clearances of forest plantations are also found. The problem is particularly serious, for example, in Nepal and Pakistan, but occurs widely in the region.

Rangeland degradation

Rangeland degradation is reduction in the capacity of natural rangelands to support livestock. It occurs as a result of excessive livestock populations, inadequate pasture management, or both..

It has not been possible to obtain quantitative estimates of the extent and severity of rangeland degradation, although these may exist in some of the grassland research institutes of countries of the region. There is no doubt, however, that the problem is widespread in all countries of the dry zone.

In Pakistan, the productivity of most of the large area of rangelands is estimated to be 1050% of its potential (Asian Development Bank, 1992a); however, there may still be the capacity for quite rapid recovery where appropriate pasture management measures are taken (N. Martin, persona! communication). In India, with some 200 M cattle, grazing pressures have caused widespread exhaustion of the stored food reserves of perennial grasses and their replacement by coarse grasses (Singh, 1988). Rangeland degradation is reported to be severe and widespread in Afghanistan (ESCAP, 1983).

As defined above, desertification refers to all types of land degradation in the dry zone of the region. It is therefore not separately assessed. Accounts, with some quantitative data, are given in reports of the Desertification Control Network for Asia and the Pacific (DESCONAP) (ESCAP, 1983, 1987, 1991b) and in country reports for Iran (Kholdebarin, 1992; Noohi, 1992) and Pakistan (Hutchinson and Webb, 1987). Desertification, described as the transformation of savanna to steppe and desert, is reported to have affected large areas of India (Singh, 1988). It is also widespread and serious in Afghanistan, Iran and Pakistan.