Stakeholders

1Water is a precious good, basic to 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.1

2It is essential that people leaves enough water to nature in order to preserve the local climate, keep a high biodiversity and perpetuate a well-functioning ecosystem. Among human needs irrigation agriculture consumes by far the largest portion of water, especially in arid regions, whereas industrial and household purposes account for only about a third of water use.

3Sharing 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 neighboring countries. Sharing water in space is in Yemen solely a national problem.

4A 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, episodic and periodic surface water, perennial rivers or lakes, groundwater or spring water. Water use should be based on a vast variety of sources.

5A 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 South Arabian period

6The centers of the South Arabian kingdoms lay on the border of the Ramlat al-Sab^catayn. 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 through an overflow outlet onto the next field or, if it was the last in the series, back into the wādī. The huge amount of water in the field was too much to be retained totally in the soil. So some of it recharged the groundwater, while on its way to the water table leaching salt left by previous irrigation. The safety of the system was provided by a weak deflector dam which—in case of an uncommonly large flood—was washed away, leaving intact the channel and fields.2 Fertility was guaranteed by the silt deposited on the fields with every irrigation event. 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, the result of sedimentation.

7In the South Arabian period almost every wādī had its extensive sayl irrigated area.3 Flat wādī floors consisting solely of silt, gullied now by erosion, tell us about it. Even the famous two gardens of the Sabaeans were irrigated in this manner because the Great Dam functioned to raise the water to the level of the oases and by no means to store water.4 So two thousand years ago farmers continuously created fertile wādī floors that are the most prosperous land reserve today.5

8At the same time the mountainous region of Yemen was quite densely populated. People there based their economy on rainfed agriculture sustained by the higher rainfall of the mountains. In order to profit from rainfall people had to level their fields so that the precious water drops were retained in the soil, and that the rain did not wash the soil away in the rugged landscape. Where the amount of precipitation required was certain, collector fields were prepared to harvest water for the prepared arable land.6 In this way, especially in the Himyarite 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.

9From the point of view of sharing water, the South Arabian period may best be summed up in the following table:

10Three 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 optimal, leaving enough for nature.

Islamic period

11The beginning of Islam brought a shift of the population in two directions. Many tribes migrated northward to take part in the military expansion of the new religion. Other groups moved from the lowland to the highland of Yemen.7 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 wādīs around the Ramlat al-Sab^catayn 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 wādī.8

12The situation in the highland did not fundamentally change. The emigration decreased the pressure on the rainfed agriculture at the beginning. But with the increase of the population in recent centuries land use reached its limit. Every possible spot on the mountain slopes served agriculture, either by being terraced or by being cleaned for use as water collecting fields. In this way the transformation by terracing of the Yemeni landscape was further intensified. Today that landscape ranks among the most beautiful man-made mountain sceneries on earth.

13Altogether 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-like vegetation with its fauna along the wādīs and the groundwater was recharged regularly. The distribution in space was dominated by the Islamic rule that farmers upstream are favored over those downstream.9 Cisterns and wells, both with limited capacities, provided the little water needed for household and religious purposes.

Modern times

14The present situation is characterized by a rapid increase of diesel-pumps across the country and by an exploding demand for water by the fast growing cities. Furthermore, one plant, qāt, dominates agriculture in the highland because of its high return of investment; qāt and a slowly emerging industrial sector appear as new consumers of water. These changes are all based on the idea that water is readily available 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.

15Beside this major shift, an outline of water-sharing features practiced today present additional minor changes.

Conclusions

16The method of examining four different aspects of water use - space, time, stakeholders, and source - leads to the following conclusions:

• More stakeholders are looking for water than in ancient times. Therefore, the stakeholders, competitive today, 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 wādīs. If less water is used in the highland it does not mean that there will be more water for the lowland.
• Because the water problem cannot be separated into parts, management of water management lies in a single hand. One institution has to handle all aspects of water use, including ecological goals.
• Surface water storage may change natural conditions. The evaporation of the new lake at Ma’rib deteriorates the local climate. 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 contrary to Yemeni tradition. Rainfed agriculture must be strengthened by the government, and traditional methods of rainwater harvesting for agricultural and domestic use must be enforced.