Rainwater harvesting

Rainwater harvesting – The concept of watershed development is important in the efficient management of rainwater. The Rainwater harvesting with storage facility should form an integral part in WDPS which has a crucial role in providing life-saving irrigation to the standing crops when they are exposed to mid-term drought and also for pre-sowing irrigation in post-rainy crops in rainfed areas. Since substantial funding is required for the creation of RWHS, it calls for public support.

Rainfed agriculture in India is practiced in about 57% of an estimated 140.3 m ha net cultivated area and India ranks first among the rainfed agricultural countries of the world in terms of both extent and value of produce. It contributes 40% of food grains and supports 40% of the population, 80% of horticulture, and 60% of livestock. The importance of rainfed agriculture is obvious from the fact that 55% of rice, 91% of coarse grains, 90% of pulses, 85% of oilseeds, and 65% of cotton are grown in rainfed areas.

Characteristics and Issues with Indian Rainfed Agriculture

Rainfed areas in India are highly diverse. It is practiced under a wide variety of soil types, agro-climatic, and rainfall conditions and is mainly concentrated in five states Rajasthan, Madhya Pradesh, Maharashtra, Andhra Pradesh, and Karnataka. The annual rainfall varies between 400 to 1000 mm which is unevenly distributed, highly uncertain, and erratic. As a result of low and erratic rainfall, a significant fall in food production is often noticed.

Rainfed agriculture in India is mainly characterized by frequent droughts, soil degradation, low soil organic content, multi-nutrient deficiencies, low external inputs, low investment capacity of farmers, and poor market linkages”. Long-term data for India indicate that rainfed areas experience 3-4 droughts per decade of moderate to severe intensity.

Also, long dry spells during the monsoon season cause severe water stress and result in partial or complete loss of crops. Land degradation in rainfed areas mainly includes soil erosion by wind and water, loss of soil humus, depletion of soil nutrients, deterioration and reduction of vegetation cover and loss of biodiversity also affects the production capacity of the land adversely.

The increased use of fertilizers alone, often in an unbalanced manner, has degraded soil quality and exacerbated multiple nutrient deficiencies. Use of external production inputs e.g. balanced nutrients, supplemental irrigation, good quality seeds, and pesticides are: lower in rainfed than in irrigated crops. Small and marginal farmers who account for major operational holdings in rainfed agriculture need credit for both consumption and investment, but the credits to these farmers from formal institutions are low and the dependence on money lenders is high.

Also, the traditional markets in rural areas are unregulated and unprofitable, and the small and marginal farmers operate independently without pooling the produce for efficient marketing. Rainfed agriculture is also more vulnerable to climate change implications than irrigated agriculture due to its poor capacity to cope with extreme water and weather shocks.

Rainwater harvesting For Upgrading Rainfed Agriculture:

The yield of food grains in the rainfed regions varies from 1-2 compared to attainable yields of more than 4 t/ha. Water has primarily been an issue in rainfed agriculture. Therefore, harvesting of surplus runoff, its storage and reuse for supplemental irrigation, and the efficient in-situ conservation of rainwater can be the potential strategy to achieve. the desired level of yields in these areas.

Prolonged dry spells during flowering, pollination, and seed formation stages of a crop are highly detrimental to yield. The use of harvested rainwater for one or two life-saving irrigations of Kharif crops during mid-season drought can increase the average yield of rainfed crops substantially.

Methods of Rainwater harvesting:

In-Situ Rainwater harvesting:

It refers to the collection of rainwater where it falls for use on the same surface (often called in situ water conservation). The methods mainly include contour bunding, field bunding, ridge and furrowing, contour trenching, and contour cultivation. The selection of a particular method depends on the topography, nature, depth of soil, rainfall intensity and amount, infiltration and water holding capacity of soils, and land use, etc. These methods increase the time of concentration and provide an opportunity for the infiltration of water. The in-situ measures are very effective in building up the soil moisture levels to sustain vegetation growth during dry spells and also contribute to groundwater recharge.

External Rainwater harvesting:

It includes all those techniques which induce collection and storage of rainfall and/or runoff for its beneficial use e.g. for raising agricultural and horticultural crops or for domestic and livestock consumption. These methods are also considered very useful for groundwater recharge both when rainfall is deficient and when there are flash floods. The various methods of Rainwater harvesting, categorized as traditional and contemporary, are briefly presented below.

Traditional methods:

Village ponds and tanks are the most commonly used methods to collect and store rainwater. Ponds are excavated in different shapes and sizes depending on the nature of the terrain, availability of land and water requirements of the village community. Pond water is generally available for 2 months to a year after the rains, depending on the catchment characteristics and the amount and intensity of rainfall.

Tankas/kunds/kundis are underground structures of various shapes and sizes to collect rainwater for drinking purpose in the desert, and arid areas of Rajasthan. These are built both for individual households as well as for village communities using locally available materials. Tanka is constructed by digging a circular hole of 3-4.25 m diameter and plastering the base and sides with 6 mm thick lime mortar or 3 mm cement mortar with stone slab coverings. Rainwater harvesting

Vav/baoli/bavadi/jhalara are traditional wells in Rajasthan and northern India. Often rectangular in design, these structures have steps on three or four sides. These ancient water harvesting systems collect subterranean seepage of a talab/lake located upstream. They were mainly set up by the nobility in cities to provide water supply to the community.

Hill slope collection system is common in many hilly areas with good rainfall e.g. in Uttarakhand, Himachal Pradesh, Meghalaya, and Arunachal Pradesh. It consists of lined channels built across hill slopes to intercept rainwater. These channels convey water to agricultural fields or to fill small ponds.

Contemporary methods:

Check dams and nalla bunding consist of an embankment across small streams and long gullies with a waste weir at suitable place. The impounded water is used by cattle or for life saving irrigation. The impounding also. facilitates the percolation of water into deeper soil and makes it possible to bring under cultivation the land under the bed of the nallas.

Percolation tanks impound Rainwater harvesting and have a waste weir to dispose of the surplus flow in excess of the storage capacity of the tanks. Percolation tanks are generally constructed on small streams or rivulets with adequate catchment for impounding surface runoff. These tanks are used entirely for recharging the aquifer through percolation.

Sub-surface barriers, constructed below river beds on impervious subsurface strata, are the most suitable artificial structure for promoting groundwater recharge in arid and semi-arid regions. Such barriers are quite suitable structures as they are safe from flood havoc, and evaporation losses and do not need elaborate overflow arrangement and periodic de-sitting.

Government Initiatives in Promoting Rainwater harvesting and their Effectiveness:

A major national initiative in India in which Rainwater harvesting is a significant component is the watershed. development program (WDP) taken up under different schemes of the Government of India (GOI) and the state governments. Scientists and engineers have developed a variety of technologies that offer solutions for different conditions. The solutions include interventions ranging from simple check dams to large percolation tanks, from vegetative barriers to contour bunds, and changes in agricultural practices.

Way Forward:

Upgrading rainfed agriculture requires the same level of concerted water governance and management priorities as given to irrigated agriculture during the past six decades. Concerted efforts are also required for building up institutional capacities, policy frameworks, knowledge generation, and public finance for Rainwater harvesting in rainfed agriculture. The concept of watershed development is important in the efficient management of rainwater.

The Rainwater harvesting with storage facility should form an integral part of WDPs which has a crucial role in providing life-saving irrigation to the standing crops when they are exposed to mid-term drought and also for pre-sowing irrigation in post-rainy crops in rainfed areas. Since substantial funding is required for the creation of RWHS, it calls for public support. Also, most RWHS are reported to have a favorable mean cost-benefit ratio.

Apart from enhancing the availability of water by RWHS, water-use efficiency needs to be increased through the adoption of modern irrigation methods like drip and sprinklers. Awareness of Rainwater harvesting and water conservation should be created among the masses through education, mass media, regulation, incentives, and disincentives.

Global warming has increased the frequency and intensity of droughts, floods, cold/heat waves, and other extreme events, and risks. Rainwater harvesting can ensure climate-smart agriculture and resilience in agriculture. The simultaneous occurrence of floods in some parts and droughts in other parts calls upon interlinking of rivers. Minimizing water storage and. conveyance losses, most efficient micro-irrigation. system and protected cultivation can ensure the optimum use of limited water resources.

Robust and climate-smart farming systems, integration of on-farm and non-farm activities, and convergence with MGNAREGA can seasonal migration. Co-generation of renewable and cheaper non-grid wind and solar energy has tremendous potential for promoting micro-irrigation, protected crop cultivation, and other power needs of arid and semi-arid regions especially all along the west coast. Unique and innovative agri-voltaic systems for doubling farmers’ income are in progress at ICAR CAZRI, Jodhpur.