Abstract
Seasonal streams (wadis) are of vital importance in dry and semidry countries including Sudan. Depending on the rainfall variability of the country, the annual discharge of such wadis was estimated to range from 3 to 7 km3 per annum. In the present study two wadi-discharge prediction methodologies were used to predict the discharge of Khor (wadi) Abu Fargha. The first methodology depends on the El Nino Southern Oscillation (ENSO) event which was divided into six distinct stages. The discharge during each stage was compared to previously estimated rainfall in the dry zone of the Sudan during the concurrent stage. The methodology was found to illustrate about 83% of the discharge behaviour of Khor Abu Fargha. This high prediction skill is attributed to the fact that the wadi is located in an area that is influenced by the ENSO event and to the availability of the discharge data for consecutive 34 years. The use of global sea surface temperatures (SSTs) in rainfall seasonal forecast studies was initiated during the 1990s through the development of empirical-statistical models. Using such methodology the models predicting Abu Fargha discharges were found to excel those for some meteorological stations and the dry zone of the Sudan as well. This is attributed to the fact that wadi discharges represent the whole catchment area whereas rainfall data represent only the rain gauge readings. The models using May global SSTs achieved better predictability in Abu Fargha discharges the thing which was found to be consistent with the results obtained in previous studies by Kassala meteorological station which is located in the vicinity of the wadi. The chapter illustrates the use of the wadi prediction information in forecasting the available storage of the aquifers and concluded that combining the different information, realistic management of surface and ground water resources can be achieved. The study recommended the use of water conservation techniques and integrated dryland management approaches.
TopIntroduction
Sudan is located in the northeastern part of Africa with an area of about 2.5 km and an estimated population of 40 million people. The river Nile system which includes the Blue Nile and the While Nile together with other tributaries and the main Nile traverses Sudan from Ethiopia and Uganda to Egypt and constitute the most important water resource of the country. It is estimated that about 35% of the population of the country live on or close to the river Nile flood plains. The desert, arid and semi-arid ecosystems occupy more than 50% of the area of the country. Meanwhile, the Savannah ecosystems cover less than 10%. The southern region of the country receives an ample amount of rainfall that exceeds 1000 mm/ annum most of which occur between March and October. However, high temperatures result in high evaporation rates. Land degradation affects both the north and the south parts of the country (El Mustsfa, 2005).
According to El Gamri (2009) the rains of the country are affected by the following:
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The position of the Inter-Tropical Convergence Zone (ITCZ).
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The three sub-tropical anticyclones (high pressure systems) around the African continent.
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The inter-hemispherical monsoonal wind systems.
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The Mediterranean depression (low pressure system).
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Easterly waves and associated jet streams.
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Meso-scale systems.
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Teleconnections e.g. with ENSO event.
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Anthropogenic influences.
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Climate Change.
Aridity which dominates about two- thirds of country enhanced conflicts over the limited natural resources to the extent that social integrity and political stability were affected. It is worth mentioning that the dry and semidry region extends to about 96% of the total geographical area in North Africa (Saeed and El Gamri, 2000).
Currently water resources management is a serious problem in the country however, due to demographic and hydro-political reasons the problem will be more drastic in the future. Meanwhile anticipated impacts of climate change on the water resources of Sudan include the following (Björklund, et al., 2009):
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The anticipated more frequent droughts will result in decreased accessibility to water for household and the other uses.
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Droughts and floods will result in deterioration in soil fertility as well as the loss of crops and livestock, thus bringing about severe food security conditions.
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Droughts will adversely impact the hydroelectric power generation on which the country is dependant to a great extent.
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Frequent droughts and less surface water also result in reduced groundwater recharge and an accentuated lack of access to water.
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Migration of both internally displaced war affected people and refugees from neighboring countries in addition to the increasing population put more pressures on water resources.
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Reduced flowing water in the swampy areas will harbor insects, plant diseases as well as vector-borne diseases and may result in loss of life.
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Secondary impacts of floods may also occur to the infrastructure.
One-six of the area of the country is under cultivation meanwhile, a quarter is devoted to forestry and pasture. Agriculture which constitutes the main occupation in the country accounts for less than 50% of its GDP although it covers almost 80% of the total exports.
Wadis are important water resources in the Sudan specially in areas remote from the Nile that are dominated by the Basement Complex or with high ground water salinity (Ahmed et al., 2004). Their use for water supply and agriculture has been practiced widely in the country. For instance the area flooded or irrigated from wadis is 300,000 fed which is equivalent to about 11% of the area irrigated from the Nile.
Key Terms in this Chapter
Wadi: An Arabic word that means a seasonal stream however, it is gaining more and more recognition in the recent literature in hydrology and water resources management.
Arid: An arid area receives rainfall of about 200 mm/annum
Water Harvesting: This term denotes ancient/ modernized practices of collecting the runoff generated from rain water for various purposes including water supply for both humans and animals, agricultural production, recharge of ground water resources an environmental protection.
Watershed: Is an area though which water flows on its way to an ocean, a sea, a river or a lake. A watershed may drain a huge area of thousands of square miles or very small of an area of 20-acre.
Management: In the context of IWRM water resources management is considered as the process of the coordinated (Participatory) management of land resources including water to achieve maximum socioeconomic development while preserving the vital ecosystems.
Forecast: From hydrological point of view forecast denotes the anticipated discharges of a seasonal or perennial stream during a certain coming season.
ENSO event: This term denotes the linkages between abnormal Sea Surfaces Temperatures (SSTs) that occur in the tropical portion of the Pacific Ocean (above normal SSTs known as El Nino and below normal SSTs known as La Nina) and the global climate systems.
Abu Fargha: A large seasonal stream that originates from the high lands of eastern Sudan and flows westwards an ultimately joins river Rahad which is a tributary of the Blue Nile. It constitutes a major water supply as well as a flood hazard to Gedarif which is a major town in the eastern part of the country.