Geography and Population
Yemen (15°00' North, 48°00' East), with a total area estimated at 527,970 km2, is located on the south-western edge of the Arabian Peninsula. Apart from the mainland it includes many islands, the largest of which are Socotra in the Arabian Sea to the far east of the country and Kamaran in the Red Sea. The country is bordered by Saudi Arabia in the north, Oman in the east, the Arabian Sea and the Gulf of Aden in the south, and the Red Sea in the west. A large part of the boundary between Yemen and Saudi Arabia has not yet been defined officially.
The present Republic of Yemen was born in 1990, as a result of the unification of the former Yemen Arab Republic (YAR) and the People's Democratic Republic of Yemen (PDRY). These two parts are sometimes still referred to respectively as the northern and southern part of the country. For administration purposes, the country is divided into 17 governorates.
The cultivable land is estimated at about 3.62 million hectares (ha), which is 7% of the total area. In 1994, the total cultivated area was 1.05 million ha, or 29% of the cultivable area, of which 0.85 million ha consisted of annual crops and 0.20 million ha consisted of permanent crops.
The total population is 14.5 million (1995), of which 66% is rural. The average population density is about 27 inhabitants/km2, but in the western part of the country the density can reach up to 300 inhabitants/km2 (lbb province), while in the three eastern provinces of the country the density is less than 5 inhabitants/km2. This is closely related to the physical environment. By far, the largest part of the population lives in the Yemen Mountain area in the western part of the country, where rainfall is still significant, although not high in many locations. The hostile environment of the desert and eastern upland areas is reflected by low population density. The average demographic growth rate is estimated at 3.7%, which is very high. In 1990, agriculture accounted for 20% of the country's gross domestic product (GDP) and employed 62% of the labor force.
Climate and Water Resources
Yemen has a predominantly semi-arid to arid climate, with rainy seasons during spring and summer, and high temperatures prevail throughout the year in low-altitude zones.
In Aden mean figures of 25°C (January) to 32°C (June) occur, but maximun temperatures over 38°C are quite common, combined with a very high relative air humidity. Mean annual precipitation on the mainland gives a volume of 93.6 km3. The average annual rainfall ranges from less than 50 mm in the coastal areas and the deserts, to 200-400 mm on the slopes of the highlands and more than 1,000 mm on the western slopes of the mountains.
The many different landscapes of Yemen can be grouped into five main geographical/ climatological regions:
- The Coastal Plains: The Plains are located in the west and south-west and are flat to slightly sloping with maximum elevations of only a few hundred meters above sea level. They have a hot climate with generally low to very low rainfall (< 50 mm/year). Nevertheless, the Plains contain important agricultural zones, due to the numerous wadis that drain the adjoining mountainous and hilly hinterland.
- The Yemen Mountain Massif: This massif constitutes a high zone of very irregular and dissected topography, with elevations ranging from a few hundred meters to 3,760 m above sea level. Accordingly, the climate varies from hot at lower elevations to cool at the highest altitudes. The western and southern slopes are the steepest and enjoy moderate to rather high rainfall, on average 300-500 mm/year, but in some places even more than 1,000 mm/year. The eastern slopes show a comparatively smoother topography and average rainfall decreases rapidly from west to east.
- The Eastern Plateau Region: This region covers the eastern half of the country. Elevations decrease from 1,200-1,800 m at the major watershed lines to 900 m on the northern desert border and to sea level on the coast. The climate in general is hot and dry, with average annual rainfall below 100 mm, except in the higher parts. Nevertheless, floods following rare rainfall may be devastating.
- The Desert: Between the Yemen Mountain Massif and the Eastern Plateau lies the Ramlat as Sabatayn, a sand desert. Rainfall and vegetation are nearly absent, except along its margins where rivers bring water from adjacent mountain and upland zones. In the north lies the Rub Al Khali desert, which extends far into Saudi Arabia and is approximately 500,000 km2 in area. This sand desert is one of the most desolate parts of the world.
- The Islands: The most important of all the islands is Socotra, where more exuberant flora and fauna can be found than in any other region in Yemen.
Yemen can be subdivided into four major drainage basins, regrouping numerous smaller wadis:
- the Red Sea basin
- the Gulf of Aden basin
- the Arabian Sea basin
- the Rub Al Khali interior basin
The floods of the wadis in Yemen are generally characterized by abruptly rising peaks that rapidly recede. In between the irregular floods the wadis are either dry or carry only minor base flows.
Surface water resources have been estimated at 2,000 million m3/year, but this quantity corresponds to the runoff from major rivers and does not include the runoff produced within the smaller catchments. Renewable groundwater resources have been estimated at l,525 million m3/year, a large part probably coming from infiltration in the river beds. A major groundwater aquifer was recently discovered in the eastern part of the country with an estimated storage of 10 km3. This aquifer is still under study and it is not known whether the groundwater is rechargeable or whether it is all fossil water.
The surface runoff to the sea measured in some major wadis is estimated at 270 million m3/year, the groundwater outflow to the sea at 280 million m3/year. There might be some groundwater flowing into Saudi Arabia, but no data are available. The existence of surface drainage crossing into Saudi Arabia suggests that some sharing of surface flows could be possible, but details are not known.
The total dam capacity is estimated at 0.18 km3. In general, the dams are built for irrigation and domestic purposes, but at the same time they contribute to groundwater recharge. There are also many flood control dams which are not intended to store water, but to divert the spate floods immediately to the adjacent irrigation network (spate irrigation).
In 1990 total water withdrawal was estimated at 2,932 million m3/year, of which 92% was used for agricultural purposes (6.9% is withdrawn for domestic use and 1.1% for industrial use). Most of the water used was groundwater (from wells and springs), resulting in groundwater depletion as withdrawal exceeds the annual groundwater recharge. The rates of decline of the groundwater levels is alarmingly high in many zones, especially in the Yemen Highlands, where decline of between 2 and 6 m/year is commonly observed. In coastal zones this leads to the incidence of saltwater intrusion. Spring-fed irrigation has reduced significantly as groundwater tables have dropped. The quantity of desalinated water was estimated at 10 million m3/year in 1989, contributing to the water supply of Aden.
Irrigation and Drainage Development
In 1994, the total water managed area was estimated at 481,520 ha. A global figure for irrigation potential is not available. About 48,000 ha have been identified for further irrigation development, mostly in the coastal plains and in Wadi Hadramaut.
Two main types of water management can be distinguished:
- Full/partial control irrigation: This concerns an area of 383,200 ha, all irrigated from groundwater, of which 363,200 ha is from tubewells and 20,000 ha from spring water. In general, new, deeper tubewells replace those which have gone out of production because of declining water tables.
- Spate irrigation: This covers an area of 98,320 ha. Traditionally, farmers in the vicinity of wadis relied on simple earth built diversion systems and irrigation networks. With small to medium spates, these temporary embankments can be effective; with large spates, they are often swept away. In order to give better control of the spate flows, a series of public sector investments, involving the construction of permanent diversion weirs and canal distribution structures, have been made in the main wadis since the early 1970s. Most of these systems, however, have experienced maintenance and water distribution problems because scheme designs conflicted with traditional water rights.
On the remaining cultivated area of 571,266 ha, water harvesting is practiced, based on collecting and retaining overland flow in zones where soils permit agriculture. The receiving zone is always smaller than the zone where overland flow is produced, thus a multiplier effect is produced which permits agricultural production in low-precipitation zones. The numerous constructed mountain terraces, also called 'the hanging gardens of Yemen', collect and retain rain and overland flow in a similar way.
Overall irrigation efficiency low, between 35 and 45%, depending on field levelling and the water conveyance system used. Sprinkler irrigation and micro-irrigation are found on a limited number of farms and in pilot projects, using water from tubewells and springs. Almost all irrigation is surface irrigation. It is thought that efficiency could be increased to 60% by lining the canals and installing pipe distribution for surface irrigation, and to over 80% by adopting sprinkler irrigation and micro-irrigation techniques.
Farm size, including both rainfed and irrigated agriculture, is very small in general: 37% of the farms have less than 0.5 ha, 72% of the farms less than 2 ha, while only 4% of the farms have more than 10 ha.
Very rough estimates of the cost of irrigation development using groundwater from tubewells lead to figures between $US 250/ha for large schemes (10 ha) and $US 450/ha for small schemes (2 ha) in the lowlands, while in the highlands the cost might vary between $US 575/ha and $US 1,300/ha respectively. The differences in cost between the lowlands and the highlands are mainly due to differences in the characteristics of the aquifers. Operation and maintenance costs vary between $US 175/ha per year in the lowlands and $US 350/ha per year in the highlands.
According to the Constitution, flowing and underground water are defined as res communis. However, a landowner has 'precedence' for water taken from a well on his land. In spring-irrigated areas, water can be attached to land in the form of 'turns', which give rights to divert the canal into the field for a fixed period of time. The 'turn' can however be detached from the land and sold or rented separately. This landowner 'precedence' has permitted the private development of deep tubewell extraction, which is in some ways in conflict with Islamic principles. Islamic and customary law has no precedent for dealing with a new technology that allows landowners to extract (and sell) unlimited quantities of water from deep aquifers, and modern law has not yet regulated it either.
The major irrigated cash crops are cotton (12,270 ha), coffee (8,060 ha), sesame (20,410 ha), tobacco, and qat. As far as the production of qat. is concerned, no official figures are available, but there have been estimates that at least one-fourth of the irrigated land is under qat production. Main cereal crops are sorghum, maize, wheat, and barley, with a total irrigated area estimated at 49,110 ha. Production of vegetables, potatoes, and fruits have increased significantly. Pulses also retain an important place. However, no figures on the area covered by all irrigated crops are available for the country as a whole. In 1994, the yield of irrigated wheat was 3.75 tons/ha as against 0.71 to 1.70 tons/ha for rainfed wheat. The yield of irrigated barley was 4.84 tons/ha as against 0.77 to 1.30 ton/ha for rainfed barley.
The flood protection area has been estimated at between 70,000 and 80,000 ha. Salinization due to irrigation exists in several regions, but no figures are available. No drainage systems are reported to exist.
The Ministry of Agriculture and Water Resources (MAWR) is responsible for formulating policies for water resources, for food security and for crops, livestock, and forestry production, and for coordinating public investment and services in the sector. The General Directorate of Water Resources is located within the Ministry with four general departments: water resources; irrigation and maintenance of water installations; farm mechanization and land reclamation; irrigation studies. Most field services are provided to farmers through decentralized Regional Development Agencies (RDAs), supported by technical services at the national level. However, the division of responsibility between MAWR, the Agricultural Research and Extension Authority (AREA) and the RDAs with respect to water management is unclear.
Responsibility for coordinating rural water supplies lies within the Water Supply Department of the Ministry of Water and Electricity (MWE).
The General Department of Hydrology is located within the Ministry of Oil and Mineral Resources (MOMR).
Trends in Water Resources Management
The successful and sustainable exploitation of the water resources in Yemen is threatened. The most serious and obvious problem is the rapid depletion of groundwater resources. Almost all the important groundwater systems in Yemen are being over-exploited at an alarming rate. The socioeconomic consequences of groundwater resources depletion are dramatic since groundwater will become too expensive for use in agriculture and, as a result, regional agricultural economies based on groundwater irrigation are doomed to collapse if the water resources are not adequately controlled. The groundwater stocks may be further reduced by groundwater salinization (in coastal areas) and groundwater pollution (in urban areas and areas of intensive agriculture). Environmental degradation occurs, for example in areas where springs have dried up. The scarcity of water leads to ever-increasing competition which, if uncontrolled, might lead to socio-economic problems.
There is an increasing awareness in Yemen of groundwater depletion. The Government of Yemen has committed itself to a sustainable use of the water resources, which was reiterated in an official statement issued at the UN Conference on Environment and Development of 1992 in Rio de Janeiro.
Water resources management in the country suffers because there is no unified central decision-making organization. Several authorities are dealing with water-related affairs with minimum integration and coordination. To solve this problem, a Presidential Decree for the establishment of the National Water Resources Authority (NWRA) was issued in October 1995, providing for the merger of the General Directorate of Water Resources of MAWR, the General Department of Hydrology of MOMR and the Technical Secretariat of the previously existing High Water Council. The main duties of the authority will be:
- to prepare water resources policies and strategies;
- to formulate water legislation and regulations along with their enforcement;
- to undertake water resources studies, evaluation and planning; and
- to carry out management at basin level, as traditional centralized management has proved to be a failure.
Measures to be implemented at field level may include the introduction of water-saving techniques (improving irrigation efficiencies, imposing a water tariff, etc.), groundwater licensing, and enforcement of pollution control regulations.
- Earthtrends: Water Resources and Freshwater Ecosystems, World Resources Institute.
- Water Resources Information in Yemen, National Integrated Water Resources Management Program of Yemen.
- Yemen National Water Resource Authority.
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