Learning from the rain catchers

In the dry steppes of Jordan, known as the badia, you can find areas where the sloping land is patterned with diamonds. Each diamond, called a negarim, is around ten metres wide and twenty-five metres long, and is bounded by low earth ridges. In the bottom corner of the diamond, where run-off gathers, you will usually find a tree. Pistachios, apricots, almonds and pomegranates are all grown in negarim, and if the catchment area is well maintained up to 80% of rainfall will find its way to the plant.

Credit:T.Oweis, ICARDA

In many dry areas, particularly those with dense populations, water tables are falling and productive agriculture is increasingly difficult. The effects are manifold: reduced income for rural communities, degradation of the land, and population movements that increase the existing strain on urban facilities. But how to restore and sustain dryland farming? Could a large scale application of indigenous water harvesting systems offer a solution? It is a possibility being explored by the International Centre for Agricultural Research in the Dry Areas (ICARDA). ICARDA research in north Africa and west Asia, has catalogued an impressive range of indigenous systems, each one developed and refined to suit local conditions of land and climate, providing water for generations of people, animals and crops. But how easy would it be to extend the use of these methods, or even to spread them to new areas?

Physical conditions such as topography, climate and soil type would be crucial for any extension programme, but equally important are the attitudes and capabilities of the 'target' farming community. Dryland people tend to have strongly rooted traditions and priorities which have supported subsistence and survival for hundreds of years. Any attempt to 'improve' their farming methods must reflect those priorities, not least because establishing and maintaining water harvesting structures demands a high level of community commitment, time, and in some cases, capital. Extension teams will also need to consider who owns the land from which the water is to be harvested. For small scale, on-farm systems the issue is less relevant, but for larger scale projects, ownership of the catchment area is critical, and the rights of downstream communities, whose normal water resources may be affected by upstream harvesting, also need to be recognised. Schemes that can balance costs and benefits for all the people in a watershed are most likely to gain long-term support.

Which crop, which system?

Choice of system and choice of crop will be closely linked. Communities are often attracted to growing high value cash crops, and when a reliable market for these exists, the incentive may be enough to secure substantial investment in a new system. But whatever crop is chosen, it will need to be tolerant of drought, which water harvesting can only partially relieve, and should be able to withstand two or three days of water-logging, which commonly occurs after heavy storms. Winter crops are a more sensible target for harvested water than summer ones; the harvested water acts as a supplement to the winter rains, boosting productivity. Farmers who try to store their winter rain for full summer irrigation tend to reduce the efficiency of the system, because so much water is lost to evaporation and seepage.

Choosing the right system also requires a detailed appraisal of land, climate and soil. Ideally catchment areas should have relatively impermeable soils so that run-off is maximised; steep slopes are often favoured because they tend to have thin soils and are difficult to farm. Target areas should have deeper soils with good water-holding capacity. Sometimes these are artificially created by farmers. In Burkina Faso, farmers dig small pits, between 30cm and two metres in diameter, and put a mixture of manure, soil and grasses in the bottom. Known as the 'zay' system, the pits are planted with annual crops like millet and sorghum. Other systems are themselves able to build up deeper soil. In southern Tunisia, for example, the beds of the steep wadis (the dry gullies that flood during rain), are crossed by jessours: high walls of earth or stone with a spillway to prevent damage from major floods. The walls trap water and sediment, creating fertile land, ideal for fig and olive trees.

Run-off ratios

Assessing the amount of harvestable run-off in a given area is also important, since it allows the farmer to calculate the right ratio between catchment and crop. Up to now little has been done to help farmers make such calculations, particularly for small-scale, field-based systems. To overcome the technical difficulties of farm level run-off measurement, ICARDA intend to use modelling techniques, combined with field experiments, to work out optimum catchment sizes relative to cropped area under a variety of conditions.

While the indigenous water harvesting systems of north Africa and west Asia hold enormous potential for dryland farmers, significant research will be needed to overcome current constraints. The majority of projects that fail succumb to either farmer unfamiliarity with the technology, conflicts over land and water rights, or inadequate analysis of rainfall, plants and soils. Addressing these problems at farmer and community level is critical, and more searching cost-benefit analysis is needed to weigh crop yields against the demands of establishing and maintaining a harvesting system. These should properly take into account indirect benefits such as reduced soil erosion or population migration. Most importantly, water harvesting techniques must be acceptable to the farmers they are intended to help.

Back to Menu