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Rail bridge at Makanya under which run off is concentratedDeluge, disputes and drought mitigation

For farmers in the semi-arid areas of the Western Pare Lowlands to the east of Kilimanjaro, the expression 'when it rains, it pours' has a particular relevance. The village of Makanya, for example, lies to the west of the Pare Mountain ranges and experiences infrequent, but intense storms. With the sloping land unable to absorb the flood, runoff fills the generally dry streambeds. By good fortune, man-made barriers - first a road and then a railway line - concentrate the water under culverts and a bridge, from where it is diverted to farmers' fields. Without such fortuitous rainwater harvesting little crop production would be possible. However, agreeing whose fields should benefit from the runoff has been a common source of conflict.

Who owns the rain?

According to Abeid Msangi, of the Soil Water Management Research Group* (SWMRG), the right to divert the flood flows was traditionally decided on whoever first laid claim to it. When overnight rains looked imminent, a farmer might even sleep with his feet in the streambed, ready to be woken by the first flows and thereby claim the water for his field. These ad hoc claims have now been formalised and are decided by the local water management committee. Owners of fields furthest from the bridge divert the water at the height of the floods, whilst closer fields are watered once the level has begun to drop. However, Makanya is not the only village to lay claim to the floodwater and if farmers from upstream villages divert the water, Makanya's fields lose out. A further agreement, assisted by SWMRG and led by Msangi and his colleagues, limits the upstream village to diverting the water during the day only, so at night the water can flow freely to Makanya village. A local 'divisional leader' mediates any disputes.

Bridging the dry spells

But access to water is not the only issue; storing excess rainfall to provide water for irrigation is becoming essential as dry spells in many semi-arid regions become more frequent and prolonged. Research into maize yields in East Africa, for example, suggests that in three years out of four, maize grown on sandy loam soils suffers from a prolonged dry spell (more than 15 days) during the critical flowering and grain filling stages. The impact on yields is devastating. As a drought mitigating measure, the villagers of Makanya have constructed underground storage tanks, with loans for the construction provided by the government's Participatory Agriculture Development Programme. However, to maximise the benefits from the harvested water, the SWMRG team has advised the villagers to use the stored water to grow high value crops. For example, provided he receives enough runoff, Mr Abdala Sekeite, says he is confident that sales of his watermelons and vegetables can generate enough income to repay the loan within three years.

Storing excess runoff is also an important strategy for Makanya's livestock farmers. Athumani Mshitu sitting in the feeder channel to his charco damAthumani Mshitu, one such farmer, has dug a large pond (charco dam) close to his house. A network of channels feeds runoff from the surrounding land into the pond, and with good rains he can harvest enough water to support his cattle herd throughout the year. While initially allowing his animals to drink directly from the pond, he has recently built a large storage tank, fed by a pipe from the charco dam and, water from the tank is now available for his cattle, vegetable garden, and for domestic use. It is difficult for Mshitu to calculate whether the investment of time and money has been worthwhile, but it has greatly reduced the household's drudgery of collecting water. In addition, he plans to improve his dairy business by using the stored water to grow pasture crops to support more productive cattle.

Virtual water-trading

The role of community and individual rainwater harvesting systems in maximising the benefits from rainfall over the course of a year are undoubtedly important and were acknowledged in a paper presented by N. Hatibu and J. Rockström at the Stockholm Water Symposium in 2004. But in years when rains fail, another approach is needed. Hatibu and Rockstrom highlight the irony that in many years, crop failure in one area may coincide with bumper harvests in another and they make a strong recommendation for developing intra-country and intra-regional trade. More specifically, they suggest the creation of food exchange mechanisms between countries - or areas within countries - so that each has a guaranteed market for surplus production when harvests are good, and a secure source of food when harvests fail.

As with Mr Sekeite from Makanya, who hopes to sell his fruit and vegetables, trade and access to reliable markets should be an integral part of rainwater harvesting schemes and food security planning.

*The Soil Water Management Research Group is based at the Sokoine University of Agriculture, Tanzania and receives funding from the Natural Resources Systems Programme of DFID.

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1st September 2005