The Thar Desert is one of the most fragile ecosystems of India. Its low and uncertain rainfall, high temperatures, high wind speeds, and a rolling sandy topography dominated by 10 to 40 m high sand dunes, provide an awe inspiring glimpse of desolation and emptiness in the western part of Rajasthan in India and adjoining part of Pakistan, between the Aravalli Hill Ranges and the fertile Indus Valley. The Desert also has occasional small stretches of sandy alluvial plains with sparse vegetation. The plains have mostly been formed by dry streams that originate from the Aravallis, but also partly by a major Himalayan stream that has long disappeared. Because of insufficient rainfall and sandy terrain, the present day streams cannot flow for long distances, and disappear in the thickness of the sand.
Despite its dryness, the Thar has its own precious natural endowments, on the strength of which it formed a hinterland to the cradle of civilization in the Saraswati-Indus Plains (circa 3300-1300 BC). Apart from its well built people, who have over the last few millennia developed a strong adaptive mechanism to the extremes of the environment, the desert also has a wealth of animal resources that thrive and perform well under dry conditions. Survival instinct under uncertain rainfall, long and severe drought, strong sun, high wind, poor soils and above all, limited water availability has compelled the desert dwellers to innovate constantly for a better sedentary life from the available land resources. This is in stark contrast to the Sahara-Sahel region of Africa where large scale transhumance is still a major adaptive mechanism.
Thar Desert has a distinctive set of traditional wisdom, at the core of which lie the themes of water conservation, mixed farming of crops and livestock, agroforestry and land care. This is unlike the history of settlement in many other deserts where animal husbandry and migration were the core concepts. Proximity to the Harappan towns and cities, a large number of which grew in the then-drying Saraswati River valley (present day Ghaggar River that once used to carry the waters of the Sutlej also, but long before the Harappans settled), meant that the desert population had an added opportunity of trading in crop and animal products, and hence an urge to evolve technologies for water conservation and dryland agriculture. Since then a system of agriculture, based on mixed cropping and animal husbandry that depended on the optimum utilisation of the capricious monsoon rainfall and the management and care of the region’s fragile land resources, became a strong asset of the region. The mixed cropping helped to take care of grain production in years of monsoon aberrations, while animal husbandry helped most during droughts, not only through sales proceeds of the live animals, but also animal products. A host of practices for land care and water conservation are in-built in the traditional customs and agricultural practices of the rural population. Practices like keeping the land fallow for some seasons to regain the soil nutrients (long fallow for 2-5 years; short fallow for a year), erecting fences around fields during summer to trap the suspended silt that blows in from the fertile plains during sandstorms (aandhi) or to prevent the soil from blowing away, lopping of trees (rather than felling) for fuel and fodder, management of permanent pastures for grazing, rotational grazing practices etc.
Unfortunately, the situation has started changing with population growth and modernisation. As the rate of change became faster, the first casualty was the system of land fallowing. Permanent pastures have become almost bereft of ground flora, and browse-worthy shrubs have become fewer, which has encouraged the non-browsable plant species to invade. Sparse natural woody vegetation on the sand dunes and low sandy hummocks has gradually become the target of fuel wood collectors, the loss of which has loosened the structure of sand, making the dunes more vulnerable to wind during the dry summer months. In the wake of the Green Revolution major changes started to happen in the neighbouring fertile plains of Punjab and Haryana, where science mediated crop production technologies showed the road to self sufficiency in agriculture, especially through the use of improved seeds, chemical fertilizers and pesticides, mechanisation of tillage and harvest and irrigation facilities.
Soon, the echo of the Green Revolution started sounding in the arid western districts of Rajasthan as well. Farmers first opted for diesel pump sets for energising their wells, especially for winter cropping. With time, as rural electrification progressed and the state ground water department moved in to sink tube wells for drinking purposes, the farmers followed suit and started sinking their own wells for irrigation. The total sown area increased from 7.8 million hectares in 1950-51 to 10.09 in 1980 and to 10.94 by 2005. At the same time, irrigated land increased from 0.363 million hectares in 1950-51 to 1.39 in 1980 and to 2.77 in 2005, where canal networks (essentially the Indira Gandhi Canal system) accounted for 43 per cent of the irrigated area, and electrified wells the remaining 57 per cent.
Tractors followed soon after electrification and their numbers swelled from 14.5 thousand in 1980 to 200 thousand by 2005. This increase is justified by the need for quick tillage and sowing operations after rains in a sandy terrain, which have to be completed within 2 days of a 30 mm rainfall event at the break of monsoon (usually early July). Otherwise, the strong sun evaporates the soil moisture and the opportunity is lost. Tractor operation, however, is antagonistic to the random distribution of trees and shrubs in a field. The easiest choice was, therefore, to uproot the trees and shrubs in the fields. The fields thus lost their uniqueness as models of traditional agroforestry. With improved irrigation, the demand for cropland increased and the tractors gradually began to climb the sand dunes, which earlier served mostly as natural rangelands and used to be brought under cropping only during good rains. Gradually, almost the whole of the sandy tract in the desert became deep ploughed by tractors, which meant destabilisation of sand over a large area. Today many sand dunes in the eastern half of the desert are under crops where tractors plough the land and sprinkler irrigation helps grow winter crops for cash.
Irrigation led to an enormous increase in crop production, especially in the winter crops that fetched large income for the farmers. Groundwater was a free commodity and the farmers were enthused by the success of irrigation, as a consequence over irrigation of the fields became common. In the canal command areas misuse of water led to water logging and salinity in many parts of Ganganagar, Hanumangarh and Bikaner districts.
At the same time, government efforts to provide drinking water to all the villages continued. The pipeline grids for drinking water helped people to avoid the drudgery of fetching water from long distances, but this also led to a neglect of the traditional water harvesting structures, many of which silted up and their catchments became disturbed and encroached upon. The examples of worst neglect can be found in the Sekhawati tract, especially in the districts of Sikar, Churu and Jhunjhunu.
The major use of groundwater is not for drinking (<15 per cent), but for irrigation (>80 per cent). As pumping of groundwater increased, the discharge from many wells began to dwindle, and the aquifers began to dry up. The affected farmers started going deeper for water, which not only escalated the cost of lifting water, but in many cases the lifted water was also found to be of poor quality. The soils were affected and the yields were reduced. Irrigated farming then became either unremunerative or difficult to pursue due to the dried up aquifers. This forced many farmers to shift back from the irrigated winter cropping to the rain fed subsistence farming in monsoon, which led to new socio cultural problems for the affected families.
Meanwhile, the sandy soil, bereft of a minimum vegetation cover and loosened by years of tractor ploughing, became more vulnerable to strong summer winds of March to June. Fortunately, the average wind speed has fallen in much of the 1990s and the 2000s from its last peak in the mid 1980s. Despite this, the atmospheric dust load has shown signs of some increase in the recent years, due mainly to the critical changes in land uses and land cover (Fig 1).
The ferocity of the wind and the attendant sand mobility during the early 1950s and 60s are still remembered as extraordinary by the local inhabitants. The sand mobilisation was so strong that it compelled the Indian Parliament to create a Desert Afforestation Station at Jodhpur, to understand the phenomenon and to stabilise the sand dunes so that the fertile lands to the east of the desert did not get encroached upon. This Station was further developed in 1959 by the Government of India with the guidance of the United Nations Educational, Scientific and Cultural Organization (UNESCO), as the Central Arid Zone Research Institute (CAZRI). It is now a major international institute for all encompassing research on the desert and has not only developed technologies for sand dune stabilisation and shelterbelt plantation, but has also stabilised many dunes across the desert to demonstrate the technology. Systematic research by CAZRI over the last five decades has produced several need based and cost effective technologies for sustainable land management and agricultural development. Unfortunately, the adoption rates of the technologies are not as desired, because of socio economic considerations like inadequate finances, illiteracy, slow land reforms, lack of trained personnel, lack of market facilities, etc., as well as due to the lure of easy money from the almost free use of water. Meanwhile, the land condition is deteriorating due to human pressure, leading to desertification, especially through wind and water erosion, water logging, salinisation and vegetation degradation, which in turn is impacting the society. Industrial pollution is gradually becoming another major threat near the urban centres.
In the present, the top three environmental issues in the desert are water availability, land quality and dust emission. While dwindling water reserves call for urgent attention to water management, threats of global warming and population pressure are not only deteriorating the land condition, but also increasing the sand mobility and atmospheric dust load. In fact, there is now the threat of double vulnerability – to natural process acceleration and resource usurpation by humans – that might reflect sharply on soil quality deterioration and performance of the existing plant species, including crops. Yields of some crops may decline by 20-30 per cent unless remedial interventions are made. As winter temperature increases, some high value crops like cumin and wheat are already getting affected. Growing summer crops (kharif) is becoming more speculative due to shifts in rainy days and rainfall intensity. Earlier the rainfall distribution during June-September was almost like a bell shape, where the maximum concentration was during July-August. This pattern is gradually showing signs of a shift towards a double peak, one in May-June and another in August-September, which compels farmers either to speculate for a July rain or to rush for out of season purchase of inputs like seeds and fertilizer, and then gamble for a good distribution of rain during the crop growth stages. There is every possibility that the summer wind strength will also gradually increase over the next few decades. When seen in the context of changes made in land tillage and the impact of empty aquifers, this may lead to a much higher potential for sand mobilisation than experienced during the last fifty years (Fig 2).
If that happens, there is a fair chance that wind blown sand will start spreading beyond the eastern border of the Thar. This process may be assisted by reactivation of the presently stable sandy landscape to the east and north of the Thar that formed parts of a Mega-Thar some 10-20 thousand years ago. These eastern sandy areas became naturally stabilised when the rainfall increased 5-8 thousand years ago, and the desert area shrank to the west of the Aravalli Hills. Since population pressure is now very high in this sandy terrain, the aquifers have become almost dry and the land surface temperature is increasing, a suitable trigger could remobilise the thick sandy areas.
To save the Thar and the land beyond from a disastrous situation, steps need to be taken urgently. These should include: increasing the green cover in the sandy terrain to minimise wind erosion and soil nutrient loss; improving water use efficiency of crops and developing heat and drought tolerance in them; management strategies to meet the challenges of increased drought and flood frequencies; improving the livestock production system as a strong alternative to crop based economy; a proper understanding and close monitoring of land surface processes; and above all water storage and conservation, mainly through artificial recharge.