Sharing Water
by Prof. Ueli Brunner
(University of Zurich, Switzerland)
Water is a precious good; it is basic for all life. Therefore sharing water means first of all sharing the water between different stakeholders, Man being just one among them. Human needs may absorb up to 40% of an ecosystem without stressing it (Cosgrove & Rijsberman 2000, p. 25).
|
|
animals |
|
plants |
|
|
|
irrigation 70% |
|
household 10% |
|
|
industry 20% |
|
|
religion 1% |
It is essential that Man leaves enough water to nature in order to preserve the local climate, keep a high biodiversity and perpetuate a well-functioning ecosystem. Among the human needs by far the largest portion is used by irrigation agriculture, especially in arid regions. For industrial and household purposes only about a third is used.
Sharing water also has to be seen in space. Where may the runoff water be used? Shall the rainwater be caught at the place where it falls? In this respect Yemen has a great advantage in comparison with e.g., Iraq or Egypt, which must share the water with neighbouring countries. Sharing water in space is in Yemen solely a national problem.
A permanent discussion about sharing water in time is going on. Shall the water be used at once or shall it be stored for later needs? May fossil water be consumed by one generation? Closely linked with this discussion is the subject of sharing water by origin. Nature presents different sources of water e.g., rainwater, episodical and periodical surface water, perennial rivers or lakes, groundwater or spring water. Water use should be based on a vast variety of sources.
A comparison of the ancient situation with the Islamic period and the modern situation leads to helpful information about how the problems of today may be solved.
The centers of the South Arabian kingdoms lay on the border of the Ramlat as-Sab'atayn. Their agricultural economy was based on the Yemeni sayl irrigation. The method consisted in catching the floods by an earthen deflector dam, conducting the water by a channel into a large walled field, which was flooded knee-deep. Surplus water flowed to the next field by an overflow or, if it was the last in a row, back to the wadi. The huge amount of water in the field was too much to be totally retained in the soil. So some of it recharged the groundwater leaching the salt of the former irrigation period on its way to the aquifer. The safety of the system was given by a weak deflector dam which - in case of an uncommonly large flood - was washed away, leaving intact the channel and fields (Brunner & Kohler 97, p. 175). The fertility was guaranteed by the silt which sedimented on the fields with every irrigation. Therefore the Yemeni sayl irrigation was, and still is, sustainable in its proper manner. The only severe problem it faced was the rising level of the fields.
In the South Arabian period almost every wadi had its extensive sayl irrigated area (Brunner 1997a, p. 192). Flat wadi floors consisting solely of silt and gullied now by erosion tell us about it. Even the famous two gardens of the Sabeans were irrigated in this manner because the function of the Great Dam consisted in raising the water to the level of the oases and by no means to store water (Brunner 00, p. 76). So two thousand years ago farmers for centuries created fertile wadi floors which are the most prosperous land reserve of today (Brunner 97b, p. 84).
At the same time the mountainous region of Yemen was quite densely populated. Due to higher rainfall people there were based on rainfed agriculture. In order to profit from rain people had to level their fields so that the precious water drops were retained in the soil and did not wash it away in the rugged landscape. Where the amount of precipitation required was unsure, collector fields were prepared to harvest water for the prepared arable land (Brunner & Kohler 97, p. 174). In this way, especially in the Himyaritic period, a second man-made landscape was shaped. As every farmer in the lowlands knows, the terraces in the highland are the best insurance against disastrous flash floods in their region.
From the point of view of sharing water the South Arabian period may best be summed up in the following table:
• in space:- highland: rainfed agriculture & rainwater harvesting
- lowland: sayl irrigation
• in time:- at once (surface water)
- slowly (groundwater)
- storage in cisterns for household
• by stakeholders:- agriculture
- nature
- household
- religion
• by source:- periodical surface water for Yemeni sayl irrigation
- rainwater for rainfed agriculture
- groundwater in small quantities
Three conclusions may be drawn. First, the highland terraces protect the irrigated fields in the lowland. Second, surface water recharges the aquifer which is used in small portions all year around. Third, the human part in utilizing water is perfect and leaves enough for nature.
The beginning of Islam brought a shift of the population in two directions. Many tribes migrated to the north to take part in the conquest to spread the new religion. Other groups moved from the lowland to the highland of Yemen (Brunner 99, p. 78). The main reason for doing so is part of the well known story of the final collapse of the Great Dam in Ma'rib. The former fertile fields fell barren. The farmers in the large wadis around the Ramlat as-Sab'atayn would have been forced to construct bigger diversion dams in order to lift the sayl onto the level of the fields. With the diminishing power of the local leaders the necessary organization was missing. So the fertile arable land on the ancient oases could not been reached anymore. The large-scale sayl irrigation gave way to a small-scale sayl irrigation along the eroded parts of the wadi (Brunner 97b, p. 84).
The situation in the highland did not change fundamentally. The emigration decreased the hardship on the rainfed agriculture at the beginning. But with the increase of the population in the last centuries land use reached its limit. Every possible spot on the mountain slopes served the agriculture either by being terraced or by being cleaned and used as water collecting field. Like this the terraced landscape of Yemen was still intensified. Today it ranges among the most beautiful man-made mountain sceneries on earth.
Altogether only little changed in sharing water. Maybe a little more water was retained in the highland than in ancient times. The portion of sayl water used for irrigation in the lowland diminished slightly so there was enough water for the rich savannah -ike vegetation with its fauna along the wadis and the groundwater was recharged regularly. The distribution in space was dominated by the Islamic law that farmers upstream are favored rather than the ones downstream (Caponera 73, p. 12). Cisterns and wells both with limited capacities provided the little water needed for household and religious purposes.
The present situation is characterized by a rapid increase of diesel-pumps all over the country and an exploding demand for water by the fast growing cities. Furthermore one plant, qat, dominates agriculture in the highland because of its high return of investment; qat and a slowly establishing industrial sector appear as new consumers of water. All these four characteristics are based on the idea that water is evident and may be used all year round. Sharing water in time has disappeared. Permanent, unlimited water use is in the head of every farmer and every housewife.
Beside this major shift an outline from the point of view of sharing water may also show the minor changes.
Sharing water
• in space:- In the highland rainfed agriculture has diminished because it is labour intensive and produces mainly food crops.
- First attempts to bring water to another region by pipes or cistern lorries are established. Urban areas are preferred to rural ones.
- The prosperous irrigated agriculture in the lowland has multiplied the demand for water in this region.
• in time:- Permanent use is common.
- The new Ma'rib dam stores periodical surface water for later use.
• by stakeholders:- The so far unchallenged claim of the agriculture is competed with by domestic and industrial users.
- The rich qat farmers define the market of water in the highland.
- Nature is losing its part of water and faces the new problem of polluted water.
• by source:- Rainwater is less used than before.
- Groundwater is widely overused.
- Periodical surface water is still diverted for irrigation.
The method above applied of monitoring the water use from four different viewpoints leads to the following conclusions:
• More stakeholders are looking for water than in ancient times. Therefore the so far competitive stakeholders should complement each other. Domestic and industrial users may first use the water but then give it back to nature properly cleaned, so it can be reused by agriculture.• The water problem has to be seen as a national issue. Highland and lowland are a combined water system. The rainfed agriculture on the terraced fields is the best protection for the sayl irrigated oases down in the wadis. If less water is used in the highland it does not mean that there will be more water for the lowland.
• The water management lies in one hand because the water problem can not be divided. A single institution has to handle all aspects of water use including ecological targets.
• Surface water storage may change natural conditions. The evaporation of the new lake deteriorates the local climate in Ma'rib. Sweet water aquifers along the sea coast become salty if they are not recharged regularly.
• In recent years the demand for water in Yemen has been satisfied mainly by groundwater. Depending on only one water source is against Yemeni tradition. Rainfed agriculture must be strengthened by the government and traditional methods of rainwater harvesting for agricultural and domestic use must be forced.
Brunner U.: The ancient Marib Dam in Yemen - an example of irrigation techniques adapted to the local environmental conditions. In: Fahlbusch H. (ed.): Water and History; Submitted papers, Sunday 19 March, p. 70-80. Second World Water Forum, ICID, 2000.
Brunner U.: Jemen - Vom Weihrauch zum Erdöl. Böhlau-Verlag Wien, 1999.
Brunner U.: Geography and Human Settlements in Ancient Southern Arabia. Arabian archaeology and epigraphy 8, p. 190-202, 1997a.
Brunner U.: The history of irrigation in the Wâdî Marhah. Seminar for Arabian Studies 27, p. 75-85, 1997b.
Brunner U. & Kohler St.: Bewässerung im Jemen. Mare Erythræum 1, p. 171-195. Staatliches Museum für Völkerkunde München, 1997.
Caponera D. A.: Water laws in moslem countries. Irrigation and drainage paper 20/1, FAO Rome 1973.
Cherchi S.: Auswirkungen des Staudammes von Ma'rib, Jemen, auf Umwelt und Gesellschaft. Master thesis, Dept. of Geography, Univ. of Zurich, 1998.
Cosgrove W. J. & Rijsberman F. R.: World Water Vision - Making Water Everybody's Business. World Water Council. Earthscan Publications Ltd., London 2000.
Uil H. & Dufour F. C.: Water Resources - Wadi Adhanah and Marib Area. Main report. Report WRAY 15, Ministry of Oil and Mineral Resources & TNO Institute of Applied Geoscience, Sana'a & Delft 1990.