Water Resources of Somalia Project Report No W-11 October 2007 Somalia Water and Land Information Management Ngecha Road, Lake View. P.O Box 30470-00100, Nairobi, Kenya. Tel +254 020 4000300 - Fax +254 020 4000333, Email: [email protected] Website: http//www.faoswalim.org. Funded by the European Union and implemented by the Food and Agriculture Organization of the United Nations Disclaimer The designations employed and the presentation of material in this information product do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations and the SWALIM Project concerning the legal status of any country, territory, city or area of its authorities, or concerning the delimitation of its frontiers or boundaries. This document is prepared by SWALIM consultant with contributions from the SWALIM team below: Alex Koton, Data Management Officer Peris Muchiri, Hydro-informatics Officer Flavian Muthusi, Water Resources Officer Hussein Gadain, Water Coordinator The document should be cited as follows: Basnyat, D. B. (2007), Water Resources of Somalia. Technical Report No W-11, FAO-SWALIM, Nairobi, Kenya Executive Summary Acknowledgement I would like to acknowledge with gratitude the close support and guidance during the preparation of this report provided by Dr. Zoltan Balint, SWALIM Chief Technical Advisor and Dr. Hussein Gadain, SWALIM Water Coordinator. I would also like to thank and put on record the support provided by the entire SWALIM team for the completion of this report. The excellent information management system, including documentary, time series and spatial (GIS) data available at SWALIM, was useful in accessing all past work and data at one location and in a short period of time. This report has used extensively the data and analyses carried out by SWALIM and partner agencies over the past years. The various technical reports on water and land resources are referred to specifically and used in this report. Last but not the least; I would like to thank FAO, Rome and FAO-SWALIM for giving me this opportunity to undertake this water resources assessment study for Somalia. Executive Summary Introduction Water and land development need reliable data and information on available resources. Somalia Water and Land Information Management (SWALIM) are trying to recover lost information from all available sources and re-establish data collection networks. The purpose of this report is to prepare a comprehensive water resource assessment of Somalia based on data collected by SWALIM and partner agencies over the past years. The report is intended to assist decision makers, donors and investors. The specific objectives of the report are: • To assess the surface water and groundwater resources and the potential for meeting domestic, livestock and irrigation water supply demands in the whole of Somalia; • To assess the water resources of the Juba and Shabelle river basins with special focus on water resources development constraints and potential; • To identify major problems and priority areas within which more detailed investigations may be carried out. As water and land resources of a river basin are inter-related and form a unit, a river basin is widely recognized as a natural unit for water resources planning and management. In this context, the water resources assessment of Somalia was carried out on the basis of a major river (drainage) basin. Although the surface water divide (catchment boundaries) may not follow strictly the groundwater aquifer boundaries, they are, however, seen to coincide generally with the major drainage basins. The general approach followed was to assess the water, land and related resources in each river basin. The assessment is based on the following major drainage basins: ii Executive Summary 1. Gulf of Aden basin 2. Darror basin 3. Tug Der/ Nugal basin 4. Ogaden basin 5. Shabelle basin 6. Juba basin 7. Lag Dera basin 8. Lag Badana basin 9. Central Coastal basin Climate and Rainfall Based on the agro-ecological zones of Somalia, the climate varies from desert in the north- eastern parts of the coastal areas of the Gulf of Aden basin and some areas in the Darror basin in the north-east; to arid and semi arid in much of the Gulf of Aden, Nugal and Ogaden basins in the central and northern regions; and to moist semi-arid in most of the Juba- Shabelle river basins in the south and in the mountainous areas of the Gulf of Aden in the north-west. The long-term mean annual rainfall varies from 93 mm in the Darror basin to 549 mm in the Lag Badana basins. While the maximum annual rainfall in the Ethiopian and Kenyan parts of the Juba and Shabelle catchment reaches 1100 to 1350 mm, the maximum annual rainfall within Somalia is a high of about 700 mm in areas around Mareere in the lower parts of the Juba and Lag Badana basins. The minimum annual rainfall is around 20 mm in parts of the northern coastal locations in Gulf of Aden. In some parts of the Darror and Nugal basins it is as low as 66 and 80 mm, respectively. Annual Potential Evapo-transpiration (PET) is between 1500 to 2000 mm in the southern river basins but exceeds 2000 mm in the northern basins (and is as high as 3000 mm in the northern coastal regions of the Gulf of Aden basin). In most locations, PET exceeds rainfall in all months of the year. In the southern basin areas, the monthly rainfall exceeds 0.5 PET in the Gu and Deyr seasons giving “growing periods” which allow some rainfed agriculture. However, in the case of the northern basins, except for few locations in the extreme north- west Somalia, even 0.5 PET exceeds rainfall in all months giving zero values for the longest growing period (LGP) in most of the areas. This is why most areas in the northern basins are not suitable for agriculture. Hydrological Analysis of the Juba and Shabelle Rivers The Juba and Shabelle are the only perennial rivers in Somalia. They are also the only rivers where long-term hydrological data are available. Based on streamflow data from 1963 to 1990, the long-term mean annual flow volumes in the Juba river at Luuq (catchment area- 166,000 km2) and at Jamama (268,800 km2) are 5.9 billion cubic meter (bcm) and 5.4, respectively. The annual flows in the Shabelle river at Belet Weyne (207,000 km2) and at Awdegle (280,000 km2) are 2.4 bcm and 1.4 bcm respectively. The annual runoff-rainfall ratios (runoff-coefficient) are about 6.5% in Juba at Luuq and 2.1% in Shabelle at Belet Weyne. Annual flows decrease as the river flows downstream. This is mainly due to various factors such as: not much contribution to flows from the Somali catchment areas; frequent occurrence of bank full condition and spilling of flood into the flood plains and natural flood relief channels;river diversions for irrigation both during low and high flow periods; and iii Executive Summary losses due to evaporation and infiltration/recharge of the groundwater along the river. It is also evident that the flow in Juba is more than the flow in Shabelle although the catchment area of the latter is larger than the former. There are considerable flow variations within a year as well as from one year to another. As the reliability of flow available is important for the design and planning of water resources, flow duration curves for the locations where long-term data are available have been prepared for all locations with long-term data. For example, the flows exceeding 50% and 90% of the time in Juba at Luuq are 152 m3/s and 12 m3/s, respectively. In the most downstream gauged location in Juba at Jamame, the 50% and 90% flows are 144 m3/s and 10.3 m3/s. In Shabelle river at Belet Weyne, the 50% and 90% flows are 61 m3/s and 7.4 m3/s, respectively. And in the most downstream gauged location in Shabelle at Awdegle, the 50% and 90% flows are 45.7 m3/s and only 0.26 m3/s. This shows that the water in Shabelle river is diverted most extensively in the dry seasons. High floods in the Juba and Shabelle are known to cause frequent problems. Flood frequency analyses of annual daily maximum streamflow values were carried out using different probability distribution functions. The 5-year, 10-year, 50-year, 100-year and 1000-year flood estimates based on the Gumbel distribution for Juba at Luuq are 1,117 m3/s, 1,338 m3/s, 1,825 m3/s, 2,031 m3/s and 2,710 m3/s, respectively. These estimates for Shabelle at Belet Weyne are 337 m3/s, 395 m3/s, 522 m3/s, 576 m3/s and 754 m3/s, respectively. Flood values in Juba are more than that in Shabelle although the catchment area of the latter is larger than the former. This is due to higher rainfall intensities as well as denser drainage networks in the upper catchments of Juba. The flood volume is not very large compared to the catchment areas of the two rivers. However, various natural and man-made causes have aggravated the flood problems in the two river basins. These may be summarized as: • River bed levels rising higher than adjacent land, due to sediment deposition; • People breaching levees to irrigate land in dry seasons; • Encroachment of natural flood plains; • Unplanned closures of natural flood relief channels; • Total break down of the existing irrigation infrastructure; • A total lack of central or local governance managing the river basin.