Presentation of the survey
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Data collection, processing and reliability
Terminology, conventions and definitions used in the survey
A massive effort has been made in the last decade to understand better the situation of water resources management and irrigation in Africa. In almost every country where water is seen as a major constraint to agricultural development, detailed studies on water resources and irrigation have been carried out. Yet it is still very difficult to obtain reliable, systematic information by country over large regions of the continent.
To address this problem, it was decided to launch a programme, later called AQUASTAT, which would use the information existing in the countries and make it available, in a standard format, to users interested in global or regional perspectives. In 1994, priority was given to the 53 countries of the African continent, and this publication is the result of that survey.
The purpose of the survey was twofold:
In order to obtain information that was as reliable as possible, the survey was developed and carried out as follows:
5. Preparation of continental tables and maps, and cross-checking the information wherever possible.
Country profiles were prepared in the official FAO language of the country (except Equatorial Guinea which was prepared in English) and are presented here as such. Tables and maps are presented in English and French.
The country profile describes the situation regarding water resources and use in the country, and especially of the irrigation and drainage subsector. Its aim is to emphasize the particularities of each country, as well as the problems encountered in rural water management and irrigation. It also summarizes the trends of irrigation in the countries, as described in the literature available. It was a deliberate choice to attempt standardizing the country profiles as much as possible. All profiles follow a single pattern, organized in sections:
Standardized tables are used for all country profiles. When information is not available, it is represented by a dash (-). As most of the data are available for only a limited number of years, the most recent reliable data are used in the tables, with an indication of the year to which they refer.
Data collection, processing and reliability
The main sources of information were:
In total 50 variables were selected and are presented in the tables attached to each country profile. They are grouped into categories corresponding to the sections of the profiles. A detailed definition of each variable is given below.
In most cases, a critical analysis of the information was necessary to ensure consistency between the different data collected for a given country. When several sources give different or contradictory figures, preference was always given to information collected at national or sub-national level and, unless proved wrong, to official rather than unofficial sources. In the case of shared water resources, comparison between countries was made to ensure consistency at river-basin level.
It remains that the accuracy and reliability of the information vary greatly between regions, countries and categories of information, as does the year in which the information was gathered. These considerations are discussed in the country profiles.
Terminology, conventions and definitions used in the survey
The following definitions have been used for the variable presented in the tables in the country profiles. They are presented in the order in which they appear in the tables.
Area of the country: (ha) The total area of the country, including area under inland water bodies. Data in this category are obtained from the United Nations Statistical Office.
Cultivable area: (ha) Area of land potentially fit for cultivation.
Cultivated area: (ha) Land under temporary (annual) crops.
Total population: (inhabitants) The figures are UN estimates for 1994.
Water supply coverage: (%) The percentage of urban and rural population with access to safe drinking water (criteria defined locally).
Average precipitation: (mm/yr and km³/yr) Double average over space and time of water falling on the country in one year. Figures computed by FAO.
Internal renewable Water resources: (km³/yr) Average annual flow of rivers and groundwater generated from endogenous precipitation.
Global renewable Water resources: (km³/yr) The sum of internal renewable water resources and incoming flow originating outside the country.
Dependency ratio: (%) The part of the global renewable water resources which originates outside the country.
Total dam capacity: (km³) The total cumulative capacity of all dams
Desalinated water: (10 6 m³/yr) Installed capacity of desalination plants.
Water withdrawal: (10 6 m³/yr) Gross amount of water which is extracted from the resources for a given use. It includes conveyance losses, consumptive use and return flow.
Agricultural Water withdrawal: (106 m³/yr) Annual quantity of water withdrawn for agricultural purposes. It includes irrigation and livestock watering.
Domestic Water withdrawal: (106 m³/yr) Annual quantity of water withdrawn for domestic purpose. It is usually computed as the total water withdrawn by public distribution networks, and usually includes the withdrawal of those industries connected to public networks.
Industrial Water withdrawal: (10 6 m³/yr) Usually, this sector refers to self-supplied industries not connected to any distribution network.
Total Water withdrawal: (10 6 m³/yr) Annual quantity of water withdrawn for agricultural, industrial and domestic purposes. It does not include other withdrawal (see below).
Other Water withdrawal: (10 6 m³/yr) This includes all other sectors: energy, mining, recreation, navigation, fisheries and environmental. Those sectors are usually characterized by a very low consumption rate.
Wastewater produced: (10 6 m³/yr) Annual quantity of wastewater produced in the country. This does not include agricultural drainage water.
Treated Wastewater: (10 6 m³/yr) Annual quantity of produced wastewater which is treated.
Reused treated Wastewater: (10 6 m³/yr) Annual quantity of treated wastewater which is reused.
Irrigation potential: (ha) Area of land suitable for irrigation development, taking into account land and water resources. It includes land already under irrigation.
Full or partial control irrigation: equipped area: (ha) Irrigation schemes executed and managed either by government, private estates or farmers, and where a full or partial control of water is achieved. Gardening is including in this category.
Surface irrigation: (ha) Part of the full or partial control area under surface Irrigation: i.e., furrow, border, basin, and flooded irrigation of rice.
Sprinkler irrigation: (ha) Part of the full or partial control area irrigated by aspersion (sprinkler).
Micro-irrigation: (ha) Part of the full or partial control area irrigated by micro-irrigation.
Percentage of area irrigated from groundwater: (%) The part of the full or partial control area irrigated from wells (shallow wells and deep tubewells).
Percentage of area irrigated from surface water: (%) The part of the full or partial control area irrigated from rivers or lakes (reservoirs, pumping or diversion).
Percentage of equipped area actually irrigated: (%) The part of the full or partial control area which is actually irrigated. Often, the whole area equipped is not irrigated for various reasons, such as lack of water, absence of farmers, damage, organizational problems, and so forth. It concerns the physical areas. Irrigated land that is cultivated twice a year is counted once.
Spate irrigation area: (ha) Area of land equipped for spate irrigation.
Equipped wetlands and inland valley bottoms: (ha) The part of cultivated wetlands and inland valley bottoms which have been equipped for irrigation with water control structures (intake, canals, etc.). Developed mangroves are included in this category.
Other cultivated wetlands and inland valley bottoms: (ha) Part of wetland and inland valley bottom which have not been equipped with water control structures but are used for cropping.
Flood recession cropping area: (ha) Area along rivers, where cultivation occurs in the areas exposed as floods recede.
Total water managed area: (ha) The sum of full or partial control irrigation equipped areas, spate irrigation areas, equipped wetlands and inland valley bottoms, other cultivated wetlands and inland valley bottoms and flood recession cropping areas. It does not include water harvesting area.
Power irrigated area as percentage of water managed area: (%) That part of the water managed area where pumps are used for water supply. It does not include areas where water is pumped with human- or animal-driven water lifting devices.
Full or partial control schemes: (ha) The areas of large, medium and small schemes, following the criteria used by the country, with the criteria given.
Total number of households in irrigation: Total number of households living directly from earnings coming out of full or partial controlled irrigation schemes.
Total irrigated grain production: (t) The total harvested quantity of cereals produced annually in the water managed area.
Harvested crops under irrigation: (ha) Total harvested irrigated area for the crop for the given year. Areas under double cropping should be counted twice. It concerns the crops cultivated in all water managed areas. If figures are only available for the full or partial control irrigation areas, it has been indicated between brackets.
Drained area: (ha) The area equipped with subsurface or open drains. Cultivated wetlands and inland valley bottoms where some kind of drainage is provided are not included in this category.
Flood-protected area: (ha) Area of land equipped with flood control structures.
Area salinized by irrigation: (ha) Total irrigated area affected by salinization as a result of irrigation. This does not include naturally saline areas.
Notwithstanding the detailed description of each variable, some problems persist due to the fact that it is not always clearly indicated in the available literature what definition has been used in computing the figures. The most frequent problems encountered in computing the figures are listed below:
Arable land: the official definition of arable land is 'land under temporary crops, temporary meadows for mowing or pasture, land under market and kitchen gardens, and land temporarily fallow-. This definition tends to equate arable land with cultivated land. In this study, 'cultivated land' has been preferred to 'rable land' and the term "cultivable land' has been used to describe the area of land potentially fit for cultivation.
Cultivable land: this term may or may not include pan or all of the forests and rangeland.
Cultivated land: some countries include perennial crops into the computation of cultivated land. The official FAO definition has been used systematically in this report. The way multiple cropping and intercropping are accounted for in the literature is not always clearly explained.
Agricultural Water withdrawal: methods for computing agricultural water withdrawal vary from country to country. A review of the figure was performed for each country, based on crop water requirements and irrigated areas, and comments were added in the country profiles to explain the figure when necessary.
Livestock Water withdrawal: some countries include it in domestic water withdrawal, others in agricultural withdrawal.
Surface and groundWater resources: it happens frequently that no attention is given to the possible double counting of water in these two categories. A critical review of the data was performed to systematically avoid double counting.
Irrigation potential: assumptions made in assessing irrigation potential vary from country to country. In most cases it is computed on the basis of available land and water resources, but economic and environmental considerations can also be taken into account. Except in a few cases, no consideration is given to the possible double counting of shared water resources. Mangrove, wetland and flood plains are usually, but not systematically included in irrigation potential.
Typology of water managed areas: it is particularly difficult to choose a typology which suits all country specificities. In this survey, the distinction was made between five broad categories of land using water for crop production (see Table 8). In some cases, distinction between flood recession cropping and cultivated wetland was not clear and an arbitrary decision had to be taken. When no distinction was possible between equipped and other cultivated wetland, all the area was accounted for in 'other cultivated wetland and inland valley bottoms..
Irrigated area: in the text, irrigated areas consist of areas equipped with hydraulic structures to provide water to the crops. It includes areas equipped for full and partial control irrigation, spate irrigation areas, and equipped wetland or inland valley bottoms. It does not include non equipped cultivated wetland and inland valley bottoms and recession cropping areas.
Drainage: equipped wetland and inland valley bottoms often have structures for drainage as well as irrigation, in which case they have been accounted for as equipped wetland and inland valley bottoms.
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