Land degradation is one of the most potential environmental threats for any nation, more so where the livelihood of people depends largely on agriculture and related land based activities. Although land degradation is common to all climatic zones of the world, its occurrence in the arid, semi arid and dry sub humid zones – the drylands, is of more concern because of the low production potentials of the land in these zones vis-à-vis high human and animal population pressures that often tend to exceed the carrying capacity of the land under prevailing doable technologies, and ultimately lead to acceleration of the natural processes.
Land degradation in the drylands is also called desertification. The major processes of desertification include wind and water erosion, waterlogging, salinisation and vegetation degradation, while industrial pollution and mine-spoils on good quality land are also fast becoming significant processes. Since the problems are more acute in the arid lands and their fringes, desertification, by common perception is a problem of the arid areas. In India the arid western part of Rajasthan and Gujarat are most vulnerable to desertification processes. Our recent assessment with the help of satellite images and extensive ground observations show that about 18 per cent area of western Rajasthan is now severely affected by desertification and 66 per cent slight to moderately, while the rest 16 per cent is largely unaffected. Wind erosion is the most dominant process, covering 76 per cent area, mostly in the dune landscape and in rainfed croplands, while water erosion is dominant in 2 per cent area – mostly in the eastern fringe, along the Aravalli Range, and salinisation in another 2 per cent of the area, mostly in the irrigated tract of the Indira Gandhi Canal command in the north west and the well irrigated south east.
In arid western Gujarat about 44 per cent area is severely affected, 53 per cent slight to moderately, and the rest 3 per cent is almost unaffected. Water erosion is the most dominant process (43 per cent), followed by salinisation (38 per cent), which however, is due to the vast expanse of naturally occurring salinity in the Great Rann of Kachchh and the Little Rann.
Wind erosion is gaining acceleration in western Rajasthan particularly due to high human and livestock pressures on the sandy landforms, reducing the plant cover through overgrazing and fuelwood collection, expansion of croplands to marginal areas without assured water supply, and deep ploughing of sandy terrain with tractors, even along the slopes of the high sand dunes. As a result, with each episode of dust/sand storm during the hot summer months, the soils get gradually depleted of the already poor reserve of silt and clay as well as plant nutrients. Broadly, the western most part with finer soils, higher wind strength, more dryness and poorer plant cover is a major source of atmospheric dust, which gets carried eastwards during the dust storms and gradually settles in the eastern part of Rajasthan and adjoining parts of Uttar Pradesh and Madhya Pradesh. Apart from erosion of topsoil containing precious little organic matter, the other major impacts of severe wind erosion are damage to crop plants, burial of good agricultural lands and infrastructure, and disruption of transportation network. Water erosion through sheet, rill and gully erosion is a dominant problem in the foothills of the Aravalli Ranges in the wetter eastern part of the desert and large parts of arid Gujarat where the sloping terrain and >350 mm annual rainfall make these areas highly vulnerable.
Salinisation is dominant in the groundwater irrigated south central part and canal irrigated northwestern part of Rajasthan. Over irrigation, lack of proper drainage in a palaeochannel dominated alluvial plain and seepage from the canals are the root causes for the rise in water table and build up of salinity in the canal command areas, while irrigation with groundwater having salinity/high residual sodium carbonate is a spoiler elsewhere. The recently commissioned Narmada Canal project in the southwestern part of western Rajasthan needs lessons from some of the environmental issues raised by the faulty water management in the Indira Gandhi Canal command area, so that the corrective measures are taken in time, especially because part of the canal network runs through areas having highly saline soils as well as saline groundwater at shallow depth.
To combat the menace of wind erosion Central Arid Zone Research Institute (CAZRI) has developed vegetative methods for sand dune stabilisation and shelterbelt plantation, both of which are now widely adopted by state agencies. It has also developed several alternate land use systems that can help increase the perennial plant cover on the land, and at the same time provide livelihood support to the rural people. Low water requiring horticultural plants like ber and locally adapted medicinal plants can also sustain livestock during droughts. For water erosion control and better utilisation of the rainfall a number of soil and water conservation and management practices have been evolved and traditional systems improved upon. These are now packaged into an integrated watershed management programme, involving rainwater harvesting for drinking and for partial irrigation, agro forestry, agronomic treatments, groundwater recharge and management, anicuts and contour bunding in upper catchments, etc. To reclaim the land degraded by high sodicity in irrigation water, CAZRI has standardised the doses of gypsum application to soils of arid region. A variety of crops are now grown in the region with sodic water after the soil is periodically treated with gypsum.
Despite these and several other low cost land management technologies, the threats of desertification are still large and continuing, especially due to slow pace of adoption of the new technologies, high growth rates of human and livestock populations, mismanagement of the resources and vastness of the problems. Adoption rates of most technologies are very slow in the arid areas due to inadequate finances, illiteracy, slow land reforms, lack of trained personnel, lack of market facilities and gender issues. Part of the emerging problem is also associated with over dependence on crop cultivation and irrigation with scarce groundwater, especially after the Green Revolution and rural electrification that opened a Pandora’s box of agricultural opportunities to farmers, with improved seeds, agronomic practices, tools and access to groundwater for irrigation. This has now resulted in expansion of the croplands to marginally suitable lands, straining the land with a ‘no rest’ cycle, inhibiting its ability to recuperate the extracted nutrients through fallowing. Moreover sheer negligence and plundering of the rangelands and small traditional pastures, which earlier used to feed the large livestock that always bailed out people during moderate to severe droughts. In fact, livestock based farming is a major strength of the arid regions, especially in areas experiencing less than 250 mm annual rainfall and prone to frequent drought. Unlike crop cultivation whose growth is partly related to storage facilities and market access, the development of livestock sector is more dependent on faster transportation network in the hinterlands, cold storage facilities for the highly perishable animal products, and growth of livestock based industries that provide incentives to the small and marginal farmers to rear animals and pasture lands for a better economy. Hopefully, technological developments this century will make it feasible to grow more crops from smaller land areas in solar powered greenhouses in the desert at reasonable cost, which would possibly use purified brackish/saline water, and by doing so the rangelands and part of the croplands may be replanted with useful horticultural and other shrubs and grasses for a thriving economy.
It is necessary that we hasten the process of land management and conservation with a view to improve the economy of the rural poor for a sustainable future. If the emerging climate simulation results are correct, which they appear to be during the current decade so far, there is every chance that from the second half of the next decade much of the region will face a long spell of moderate to severe drought that might continue to the third decade with some breaks of good years but some having flood causing, high intensity rainfall. Overall, with the enhanced dryness that would set in, higher wind strength that would follow, plundering of the soil resources, natural vegetation and groundwater that is currently ongoing, and a general apathy towards land care might make situation worse. Unless we gear up efforts to increase the perennial vegetation cover several fold, link it with alternate livelihood development for economic well being, start conserving water and make sincere efforts to recharge our depleted groundwater aquifers, there is every chance that high incidence of sand/dust storms would start engulfing our prime cultivated lands and contiguous areas in the wetter east would turn more threatened. The arid parts of Gujarat might face a greater problem of water erosion, as rainfall amounts and intensity are gradually increasing in the region. In fact the Saurashtra area is seeing an increased time averaged monsoon rainfall intensity during the last ten years from ~0.2 mm per hour to ~0.9 mm per hour. Since the soil depth is low and slope is high, higher rainfall intensity leads to faster depletion of topsoil unless adequate conservation measures are in place. Finally, not all the impacts of global warming are yet properly understood, so tailor made technological solutions for the current weather variability developed so far might not deliver if the conditions differ in detail. We need to monitor the changes and their impacts closely to apprise all with best adaptation and mitigation measures.