Water is one of the most precious commodities for survival of mankind. Nowhere is this more true than in a desert. Survival instinct has compelled the desert dwellers historically to search for water, both surface and groundwater, to cluster near water sources, to find ways to use water perfunctorily, and to develop water conservation practices. Western Rajasthan, which contains the major part of the sandy Thar Desert of Indian subcontinent, is no exception when traditional practices for water conservation are counted upon, whether for drinking or for cultivation.
A large number of nadis (ponds) and tankas (cisterns), dot the arid plains, as well as baoris–a system of bringing water from the catchment to an enclosed and protected location in older urban centres for community use. There were other important water conservation structures also in the desert, like khadins in the western districts of Jaisalmer and Barmer that were possibly developed and perfected by the Paliwal Brahmins to conserve rainwater for winter cropping. Groundwater wells were not too many in the past, but wherever they were sited, they received utmost care for use as a source of drinking water. Despite the fact that fetching water was always a major human activity in the past that took much of human energy and time, and at places involved long distance travel (especially by women and children), the water sources always received proper attention and care.
Also amazing is the number of trees and shrubs that abound in the sandy plains of the Desert despite the hostile climate. It testifies to a long, time tested tradition of maintaining agro-forestry, so that plants surviving on deep groundwater can provide some food, fodder and fuelwood even during the frequent droughts. Broadly, three out of five years experience drought of some magnitude.
Western Rajasthan is, indeed, rich in traditional water harvesting and conservation systems. Yet, despite this richness, and despite having a sizeable knowledge bank on water use/conservation systems, compulsions of modern era developments have gradually turned the region poor so far as water availability and workable traditional water harvesting systems are concerned. Sadly, it started with rural development and more specifically with groundwater irrigation that turned much of the desert green. In this paper we chalk out how it happened, what are its present implications and what could be the likely worst-case scenario if the trend continues.
During 1950-51 western Rajasthan had a total sown area of about 7.8 million hectare (mha), of which about 363 thousand hectare was under irrigation, almost exclusively through canals in the northern part. Groundwater irrigation was very little because of the non availability of energised pumps and electricity in most of the rural areas. The sources of drinking water were mainly the village nadis and tankas, and also open wells in areas where potable water was located. The scenario began to change fast from the early 1970s when rural electrification got a major boost, and was followed closely by a vigorous campaign to make drinking water available to every village in the desert through pipelines. This was also the time when green revolution began to turn Punjab plains into the country’s food basket, with improved seeds of crops, fertilisers, pesticides, other improved agro-technologies and irrigation facilities, all at a discounted price. Soon, the echo of green revolution started sounding in the arid western districts of Rajasthan. Farmers opted for diesel pump sets for energising their wells. With time, as rural electrification progressed and the state Ground Water Department (GWD), one of the most knowledgeable and efficient state agencies, moved in its wake in search of potential aquifers and then sinking of tube wells for drinking purpose, the farmers followed their footsteps to sink their own for irrigation. By 1980 the net sown area increased to 10.09 mha, out of which 1.39 mha was under irrigation. Canals served 49 per cent area of the total irrigated, while tube wells served another 48 per cent. By 2005 the sown area increased marginally to 10.94 mha, but irrigated area increased to 2.77 mha. Canal networks now served 43 per cent area, while tube wells served 57 per cent. This was reflected in huge increases in crop production. Winter crops like wheat, mustard, cumin, etc., as well as vegetables, got a huge fillip due to high market demands. The downside was that water use efficiency of the crops was about 50 per cent of the potential, as farmers continued to practice over irrigation amounting to mismanagement of the precious water.
At the same time, pipeline grids for drinking water on one hand helped people to avoid the drudgery of traversing long distances, but on the other also translated into neglect for traditional water harvesting structures, many of which were silted–their catchments 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.
Gradually the discharge from many wells began to dwindle, and aquifers began to dry, as recharge of aquifers in this arid region is exceedingly slow and episodic due to low and erratic nature of the monsoon rainfall. As affected farmers started foraging deeper for water, not only the cost for lifting water became higher but in most cases the lifted water was found to be of poor quality, which threatened the soil and reduced yield. As input cost of irrigated farming became prohibitive and some of the aquifers became dry, land use again started to shift back in many affected farms from irrigated winter cropping to rainfed summer cropping, with implications for farm income and socio-cultural consequences for affected families.
Currently about 80 per cent of the extracted water is being utilised for irrigating crops, while only 10 per cent is used for drinking water. The dwindling groundwater reserve has also started affecting the drinking water supply scheme as demand for safe drinking water could not be met in full due to very high extraction for irrigation.
Several assessments based on actual monitoring of the region’s groundwater wells by GWD have shown how the category of different groundwater blocks gradually shifted from ‘safe’ to ‘semi-critical’ to ‘critical’ and then to ‘over-exploited’*. The worsening situation has compelled the State to put restriction on further digging for groundwater in one block of Nagaur district, two blocks in Sikar district and three blocks each in Jalor and Jhunjhunu districts. Despite the negative changes groundwater irrigation is still expanding within the desert, and aquifer conditions are becoming worse.
Measurement of groundwater extraction or any other activity that influences the earth’s gravity is now possible through satellite sensing. A pair of recently launched satellites, together called GRACE (Gravity Recovery and Climate Experiment), were launched in March, 2002 by NASA and the German Research Institute for Aviation and Space Flight, which are now orbiting the earth at a height of 500 kms and maintaining a satellite-to-satellite distance of about 220 kms, to detect subtle changes in the earth’s gravitational pull due to local changes in Earth’s mass. In a recent landmark study based on analysis of GRACE data scientists have shown (Rodell, Velicogna and Famiglietti, Nature, 2009; vol. 460, pp. 999-1002) that between 2002 and 2008 groundwater exploitation along the arid fringe in Punjab, Haryana and Rajasthan was so much that the average rate of decline in water level was 330 mm per year, which is equivalent to about 17.7 cubic kilometers of water, and exceeded the earlier estimate by the Ministry of Water Resources, Government of India by 4.5 cubic kilometers. The total extraction during the 6-year period is calculated as 109 cubic kilometer.
Considering that climate change is leading to a rise in temperature in the region, the demand for water by the humans, animals and crop plants are increasing. Added to this is the increasing human and livestock population. All these are going to increase the demand for water. According to a policy paper of the government of Rajasthan in 2005 the State may require 45.1 billion cubic metre (BCM) of water by 2015 to meet demands of domestic use, livestock, irrigation, etc., of which 17.4 BCM is to be provided by groundwater. On the other hand, the available groundwater may not exceed 7.5 BCM. Recycling of irrigation water, may provide additional 6.5 BCM water. That leaves a shortfall of 3.4 BCM under the best guess scenario! Taking surface and groundwater together, the shortfall is expected to be 9 BCM.
The above studies tend to justify our argument that if groundwater irrigated area proliferates without aquifers getting adequately recharged and land conservation measures are not strengthened, there is every possibility that groundwater irrigation system will gradually collapse. Since the deep sandy areas served by groundwater irrigation are deep-ploughed with tractors, and necessarily involves clearing of perennial plant cover (trees and shrubs) for farm operations, the collapse of irrigated farming might pose a major threat of wind erosion, and much higher atmospheric dust load. The depletion of groundwater will also increase the water quality problem, and put further stress on drinking water availability.
The major thrust for tackling the emerging problems should be creation of underground water banks in different aquifers. This requires development of technologies for faster groundwater recharge and creation of large facilities to capture rainwater. Even if technologies are perfected in time and systems are in place, uncertainties might still prevail in recharging of the aquifers because rainfall will most likely remain erratic. Under such circumstances we can only hope that a few high-rainfall events like the one in Barmer district in 2006, or the one in Nagaur district in 1975 would lead to natural flooding of the interdune plains, followed by slow recharging of the surrounding aquifers.
An analysis of the Normalised Difference Vegetation Index (NDVI) values over Thar Desert during February, derived from NASA’s AVHRR satellite sensors for the period 1982 to 2001 revealed that although the area under irrigated cropping expanded during the period, there were noticeable decline in NDVI values in some areas, which could be related to abandoning of irrigated winter crops due to groundwater depletion (Fig. 1). In some areas the change in land use is so glaring that this could be seen even without any special processing (Fig. 2 & 3).
At the same time traditional water harvesting structures need to be strengthened and improved upon, while creating new facilities. Central Arid Zone Research Institute (CAZRI) has developed a number of improved designs of traditional water harvesting structures, which are used by the executing agencies.
Groundwater irrigated agriculture will continue in the desert especially because demands for farm outputs will remain and the need for feeding the growing population will continue. What is needed under such scenario is to ensure water use efficiency of crops, and putting as much land as feasible under drip and sprinkler systems. Water shortage has already compelled the farmers in many areas in the desert to opt for these devices.
* Safe: Stage of groundwater development is <70 per cent, and pre-monsoon and post-monsoon water table do not show a falling trend. Stage of groundwater development 70 to <90 per cent, but pre and post-monsoon groundwater levels do not show a significant long-term decline.
Semi Critical: Stage of groundwater development 70-90 per cent, and water table in either pre-monsoon or post-monsoon stage shows falling trend.
Critical: (i) Stage of groundwater development >90 per cent, but pre or post-monsoon water table shows a falling trend. (ii) Stage of groundwater development <100 per cent, and water table during both pre and post-monsoon periods show a falling trend. (iii) Stage of groundwater development >100 per cent, but either pre or post-monsoon level does not show significant long-term decline.
Over exploited: Stage of groundwater development is >100 per cent, and water table during both pre and post-monsoon periods show a falling trend.