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Irrigation Schemes (irrigation + scheme)

Distribution by Scientific Domains

Engineering	41%
Earth and Environmental Science	23%

Selected Abstracts

Government Intervention in the Muda Irrigation Scheme, Malaysia: ,actors', expectations and outcomes

THE GEOGRAPHICAL JOURNAL, Issue 3 2000
CLARE L. JOHNSON
At the dawn of the third millennium the problems associated with large-scale irrigation lie largely unresolved. The outcomes of government policies rarely correspond with expectations, leading to conflict and misunderstanding between federal governments, local agencies and farmers. This paper examines the mis-match of expectations between policy implementors and policy recipients in the implementation of one government policy (tertlary intervention) in the Muda irrigation scheme, Malaysia. The findings illustrate that this policy is not achieving the productivity increase or water saving expectations for which it was designed. Instead, tertiary intervention has increased the capacity of the farmers to unofficially control the distribution and supply of the water resource and to engage in off-farm productive and non-productive activities. This results in: a significant over-supply of water; the inefficient use of this supply; and a reduction in yields without a reduction in incomes. Importantly, tertiary intervention has enabled the farmers to diversify their livelihood strategies whilst retaining access to the rice-farming culture. The findings presented in this paper serve to illustrate the significance of ,actor'expectations on policy outcomes and agrarian change. [source]

Remotely sensed data used for modelling at different hydrological scales

HYDROLOGICAL PROCESSES, Issue 8 2002
Peter Droogers
Abstract There is a growing awareness that water will be one of the most critical natural resources and that there is a need for better management of the limited water resources. This paper reports on a study of a water-scarce river basin in western Turkey. Hydrological analyses, emphasizing water use for irrigation, are performed at three different spatial scales (field scale, irrigation scheme scale and basin scale) using two kind of model: a parametric basin-scale model and a physically based crop-scale model. Data accessibility for this basin, especially for areal data, was low. A combined use of public domain data sets and remotely sensed data was used to solve this problem. A public domain digital elevation model was used to generate the streamflow network and the distances and slopes to streams. Land-cover data and leaf area index data were derived from public domain NOAA,AVHRR images. For one irrigation scheme in the basin, detailed areal water balances were obtained from the simulation model and a comparison was made between a normal and a water-short year. At the basin scale, observed flows were compared with simulated flows. It is concluded that remotely sensed data and other public domain data can be used with simulation models at different scales to create a powerful tool to evaluate water resources in a basin context. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Salinity patterns in irrigation systems, a threat to be demystified, a constraint to be managed: Field evidence from Algeria and Tunisia,

IRRIGATION AND DRAINAGE, Issue S3 2009
S. Bouarfa
irrigation; gestion de la salinité; alcalinité résiduelle; perception des agriculteurs et stratégies; Maghreb Abstract Salinity problems induced by irrigation are often presented in the literature as a threat that can only be managed at the irrigation scheme scale by installing subsurface drainage. On the other hand, salinity is a constraint that has often been successfully managed locally by farmers adapting their practices. However, the continuing expansion of irrigation with related water scarcity problems plus the increasing use of groundwater of marginal quality has resulted in a new challenge that is difficult to handle at the farm level only. To assess the dynamics of soil salinity and water quality together with farmers' salinity management practices, we adapted a common approach to analyze two contrasted salinity patterns: a traditional salinity pattern in an oasis (Fatnassa, Tunisia), and a recent sodicity pattern in a large irrigation scheme (Lower Chelif, Algeria). This approach which combines surveys on farmers' perceptions and practices and salinity measurements and geochemical analysis paves the way for more integrated management of salinity problems related to water scarcity. Copyright © 2009 John Wiley & Sons, Ltd. Les problèmes de salinité en systèmes irrigués sont souvent présentés dans la littérature comme une menace dont la seule solution réside dans l'installation de systèmes de drainage. La salinité est cependant une contrainte qui peut également être gérée localement avec succès par les agriculteurs par une adaptation de leurs pratiques. Le développement continu de l'irrigation et les tensions sur l'eau qui en découlent contraignent à un usage accru d'eau de nappe de mauvaise qualité dont les conséquences sont difficilement maitrisables à la seule échelle de l'exploitation. Ce nouveau contexte nécessite le développement de nouvelles approches permettant d'appréhender à la fois les processus de salinisation et d'adaptation des agriculteurs. Nous avons adopté une démarche commune pour évaluer la dynamique d'évolution de la salinité et les pratiques des agriculteurs dans deux situations contrastées: un schéma de salinisation classique (oasis de Fatnassa, Tunisie) et un schéma récent d'évolution vers un processus de sodisation (plaine du Bas-Chelif, Algérie). L'utilisation de cette approche qui combine des enquêtes sur les perceptions et les pratiques des agriculteurs, des mesures de salinité et des analyzes géochimiques ouvre des perspectives pour une vision et une gestion plus intégrée des problèmes de salinité liés à la pénurie d'eau. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Field evaluation of ultrasonic flowmeters for measuring water discharge in irrigation canals,

IRRIGATION AND DRAINAGE, Issue 2 2009
David Lozano
mesure de débit; débitmètres acoustiques; canaux d'irrigation Abstract Measuring water flow is essential for sound irrigation management. New commercial flowmeters based on acoustic technology have become popular for measuring water discharge in open channels of irrigation schemes in Spain and various other countries. There are two main types of acoustic flowmeter: transit-time and Doppler. We tested a commercial instrument of each type (a Risonic 2000 and an Argonaut-SW, respectively) in the field throughout an entire irrigation season. The instruments were installed in rectangular cross-sections of one of the secondary canals in the B-XII irrigation scheme, Spain. The discharges tested varied from 0.1 to 4,m3,s,1. To obtain reference data, we used a propeller current meter to measure the flow velocity across the test canal sections. Both the Risonic 2000 and Argonaut-SW instruments provided measurements that were highly consistent with those obtained from the propeller meter. The Argonaut-SW, mounted at the bottom of the canal, had to be reinstalled twice during the irrigation season since it was displaced by debris dragged by the flowing water. The Risonic 2000, mounted on the canal walls, operated without interruption during the entire season. Copyright © 2008 John Wiley & Sons, Ltd. Mesurer les débits est essentiel pour une saine gestion de l'irrigation. Les nouveaux débitmètres commerciaux basés sur la technologie acoustique sont désormais bien connus pour mesurer les débits dans les canaux des périmètres irrigués en Espagne et divers autres pays. Il y a deux types principaux de débitmètres acoustiques: temps de transit et Doppler. Nous avons examiné au champ pendant toute une campagne d'irrigation un instrument commercial de chaque type (un Risonic 2000 et un Argonaut-SW). Les instruments ont été installés dans des sections transversales rectangulaires d'un des canaux secondaires du périmètre irrigué B-XII en Espagne. Les débits analysés ont varié de 0.1 à 4,m3,s,1. Pour obtenir des données de référence, nous avons utilisé un moulinet courant mesurant la vitesse d'écoulement à travers les sections du canal testé. Les deux instruments Argonaut-SW et Risonic 2000 ont fourni des mesures tout à fait conformes à celles obtenues avec le moulinet. L'Argonaut-SW, monté au fond du canal, a dû être réinstallé deux fois pendant la campagne d'irrigation car il a été déplacé par des déchets transportés par l'eau. Le Risonic 2000, monté sur les murs de canal, a fonctionné sans interruption pendant toute la campagne. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Irrigation Externalities and Agricultural Sustainability in South-eastern Nigeria

JOURNAL OF AGRICULTURAL ECONOMICS, Issue 3 2004
Kevin C. Urama
Agricultural intensification by irrigation is increasingly regarded as the key to solving food supply problems in Sub-Saharan Africa. Conversely, mounting empirical evidence suggests that irrigation externalities might preclude long-term sustainability of arable agriculture. Choosing between intensive irrigation schemes and less intensive farming systems is therefore, problematic. The paper examines the implications of irrigation intensification in south-eastern Nigeria using adjacent rain-fed farms as the counterfactual. The analyses found mixed results. When first introduced, the irrigation scheme increased marginal factor productivity and gross margins but this has subsequently declined to the extent that the marginal factor product of land has become negative. The annual yields of the irrigated farms were also less stable than those of the less intensive rain-fed farms. These results indicate the dilemma that irrigation externalities present to sustainable agricultural policy and suggest a need to look again at the potential for developments in rain-fed systems. [source]

Using farmer knowledge to combat low productive spots in rice fields of a Sahelian irrigation scheme

LAND DEGRADATION AND DEVELOPMENT, Issue 4 2004
P. J. A. van Asten
Abstract In the oldest sections of Burkina Faso's largest irrigation scheme in the Sourou Valley (13°,10,,N, 03°,30,W) rice (Oryza sativa L.) yields dropped from about 5 to 6,t,ha,1 in the early 1990s, shortly after establishment of the scheme, to 2 to 4,t,ha,1 from 1995 onwards. Farmers blamed this yield decline on the appearance of 2 to 20,m diameter low productive spots. According to farmers and field measurements, the low productive spots decreased yields by 25,50 per cent. The low productive spots are caused by Zn deficiency. Low Zn availability is related to the very low DTPA-extractable Zn content of the soil (0·08,0·46,mg,kg,1), the alkaline-calcareous character of the soil, the non-application of Zn fertilizers, and a relatively large P fertilizer dose (21,kg,P,ha,1). Farmers were correct in relating the calcareous nature of the soil to the presence of the low productive spots. They were instrumental in identifying application of decomposed organic resources (e.g. rice straw at 5,t,ha,1) as a short-term solution that increases yields by 1·5 to 2·0,t,ha,1. Application of Zn fertilizer (10,kg,Zn,ha,1) in 29 farmer fields in the 2001 dry season eradicated the low productive spots and increased yields from 3·4 to 6·0,t,ha,1. Although application of Zn fertilizer is strongly recommended, it is not yet available in Burkina Faso. Based on a comparison of fertilizer prices on the world market and the local market, we expect that the use of Zn fertilizers will be highly profitable (cost/value ratio,,,2). Despite the relatively recent introduction of irrigated rice cropping, most farmers showed a good understanding of cropping constraints and possible solutions. Both farmers and researchers mutually benefited from each other's knowledge and observations. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Government Intervention in the Muda Irrigation Scheme, Malaysia: ,actors', expectations and outcomes

Field evaluation of ultrasonic flowmeters for measuring water discharge in irrigation canals,

Water use and productivity of two small reservoir irrigation schemes in Ghana's upper east region,

IRRIGATION AND DRAINAGE, Issue 2 2008
Joshua W. Faulkner
irrigation; gestion des ressources en eau; développement international; petit réservoirs Abstract To examine the impact of small reservoir irrigation development in Africa, the performance and productivity of two small reservoirs and irrigation schemes in the Upper East Region of Ghana were investigated in this study. Hydrologic data measured included daily irrigation volumes and daily evaporation. Farmer cost inputs, excluding labor, and harvest data were also recorded. There was a strong contrast in water availability between the two systems, the Tanga system having a higher amount of available water than did the Weega system. The concept of relative water supply was used to confirm this disparity; Tanga was an inefficient system with a relative water supply of 5.7, compared to a value of 2.4 for the efficient Weega system. It was also concluded that the dissimilar water availabilities resulted in the evolution of very different irrigation methods and coincided with different management structures. Where there was more water available per unit land (Tanga), management was relaxed and the irrigation inefficient. Where there was less water available per unit land (Weega), management was well structured and irrigation efficient. The productivity of water (US$ m,3) of the Tanga system was half that of the Weega system, when analyzed at a high market price for crops grown. In terms of productivity of cultivated land (US$ ha,1), however, the Tanga system was 49% more productive than the Weega system. The difference in the productivity of land is primarily a result of increased farmer cash inputs in the Tanga system as compared to the Weega system. The difference in the productivity of water can be attributed to the varying irrigation methods and management structures, and ultimately to the contrasting water availability. Copyright © 2008 John Wiley & Sons, Ltd. L'impact du développement de petits réservoirs d'irrigation en Afriques est étudié en analysant la performance et le bénéfice économique de deux petits réservoirs avec de différents schèmes d'utilisation dans une région au nord-est du Ghana. Les données hydrologiques utilisées dans cette étude comprennent les volumes journaliers d'irrigation, ainsi que des mesures journaliers d'évaporation. En outre les coûts des investissements des agriculteurs ainsi que des données de récoltes ont été enregistrés. La quantité d'eau disponible était considérablement différente dans les deux systèmes: les ressources en eau du système de Tanga étaient nettement supérieures par rapport à celles du système de Weega. Le concept de l'approvisionnement relatif en eau a été utilisé pour démontrer cette disparité: Tanga avait un système inefficace avec un taux d'approvisionnement relatif en eau de 5.7 comparé à un taux de 2.4 du système efficace de Weega. Il a été conclu que les différences au niveau de la disponibilité d'eau sont à la base d'une évolution de méthodes et s'accordent avec de concepts de gestion d'irrigation très contrastés. Quand il y avait plus d'eau disponible par unité de surface (Tanga), la gestion était peu organisée et l'irrigation moins efficace. Par contre, quand les ressources en eau étaient limitées (Weega) la gestion était bien structurée et l'irrigation très efficace. En termes d'eau les agriculteurs de Tanga recevaient seulement la moitié du bénéfice économique des agriculteurs de Weega quand le prix du marché était élevé pour les produits récoltés. Par contre, en termes de surface cultivée, les agriculteurs de Tanga faisaient 49% plus de profit par rapport aux agriculteurs de Weega. La différence du bénéfice économique de la terre cultivé est principalement une conséquence des investissements élevés des agriculteurs dans le système de Tanga comparé au système de Weega. La différence du bénéfice économique de l'eau peut être attribuée aux variations des méthodes d'irrigation et des structures de gestion et donc finalement aux disponibilités en eau très contrastées. Copyright © 2008 John Wiley & Sons, Ltd. [source]

The effect of introducing pipelines into irrigation water distribution systems on the farm economy: a case study in the Southern Governorates Rural Development Project, Republic of Yemen,

IRRIGATION AND DRAINAGE, Issue 1 2001
Rozgar Baban
le Yémen; eau souterraine; irrigation; tuyaux Abstract The Southern Governorates Rural Development Project (SGRDP) is a comprehensive participatory rural development project covering three of the five southern Governorates of the Republic of Yemen, namely Hadramaut, Abyan and Lahij. Its objective is to alleviate poverty in rural areas of these three Governorates. A major component of the project is to develop virgin lands for agriculture and allocate each 5 feddan (FD) plot to those farmers who do not own land (1 FD=4200 m2). As the annual rainfall in the project area is less than 100 mm and since landlords and other farmers already own lands suitable for agriculture in the major wadis, the only source of irrigation water in the newly developed land is the groundwater (GW). The SGRDP is aware of the scarcity of water resources in the country, particularly in the project area; it therefore makes every possible effort to optimize the use of GW for irrigation by practical means. One way of reducing GW used for irrigation is by replacing major canals in the farms by buried pipelines. This method has been tried in small-scale individual farms outside the project area and it proved that farmers could adapt to the system without difficulty. Sprinkler and drip irrigation systems have been tried in many previous agricultural development projects in the country but with no apparent success, as far as the farmers' adoption of the method is concerned. Thus, the project, as the first stage to reduce the use of GW for irrigation in the newly developed areas, planned to eliminate, initially, the conveyance losses by replacing the open canals by buried PVC pipes. In this paper, it is attempted to show that the use of buried pipes in small scale irrigation schemes is financially feasible, even if the indirect and non-tangible environmental benefits are not considered. This paper deals only with special GW schemes recommended for the project area; however, the outcome could be generalized and applied elsewhere in the country. Copyright © 2001 John Wiley & Sons Ltd. Le Projet de Développement Rural des Gouvernorats du Sud (SGRDP) est un ensemble de projet de développement rural participatif de trois des cinq Gouvernorats de la République de Yémen à savoir Hadramaut, Abyan et Lahij. Son objectif est d'atténuer la pauvreté dans les régions rurales de ces Gouvernorats. L'une des principales activités de ce projet concerne le développement des terres incultes pour l'agriculture. Ce développement passe par l'allocation de parcelles de 5 FD à chaque agriculteur sans terre. Comme la pluviosité annuelle dans cette région est inférieure à 100 mm et que les propriétaires et les autres fermiers disposent déjà des terres aptes à l'agriculture dans les WADIS importants, l'eau souterraine est la seule source d'eau pour l'irrigation des terres nouvellement développées. Compte tenu de la rareté des ressources en eau, particulièrement dans la région du projet, le SGRDP s'efforce d'optimiser l'utilisation de l'eau souterraine (ES) pour l'irrigation en adoptant des moyens pratiques. L'un des moyens de réduire l'ES utilisée en irrigation consiste à remplacer les principaux canaux des fleuves par des tuyaux enterrés. Cette méthode a été utilisée à titre d'essai dans des exploitations individuelles de petite taille en dehors de la région du projet, et il s'est avéré que les agriculteurs peuvent s'adapter à ce système sans difficultés. Les systèmes d'irrigation par aspersion et goutte à goutte ont été essayés dans de nombreux anciens projets de développement agricoles du pays, mais sans succès apparent quant à l'adoption de cette méthode par les fermiers. Ainsi, le projet, en tant que première stade de réduction de l'ES pour l'irrigation dans les régions nouvellement développées, a proposé d'éliminer au début les pertes par transport en remplaçant les canaux ouverts par des tuyaux PVC enterrés. Ce rapport essaie de montrer que l'utilisation des tuyaux enterrés dans les projets d'irrigation de petite taille, est faisable du point de vue économique même en faisant abstraction des avantages indirects et non tangibles provenant de l'environnement. Le rapport traite seulement des projets spéciaux de l'ES recommandés pour la région du projet. Cependant, les résultats peuvent être généralisés et appliqués aux autres régions du pays. Copyright © 2001 John Wiley & Sons Ltd. [source]

Irrigation Externalities and Agricultural Sustainability in South-eastern Nigeria

Drought and salinity: A comparison of their effects on mineral nutrition of plants

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2005
Yuncai Hu
Abstract The increasing frequency of dry periods in many regions of the world and the problems associated with salinity in irrigated areas frequently result in the consecutive occurrence of drought and salinity on cultivated land. Currently, 50% of all irrigation schemes are affected by salinity. Nutrient disturbances under both drought and salinity reduce plant growth by affecting the availability, transport, and partitioning of nutrients. However, drought and salinity can differentially affect the mineral nutrition of plants. Salinity may cause nutrient deficiencies or imbalances, due to the competition of Na+ and Cl, with nutrients such as K+, Ca2+, and NO. Drought, on the other hand, can affect nutrient uptake and impair acropetal translocation of some nutrients. Despite contradictory reports on the effects of nutrient supply on plant growth under saline or drought conditions, it is generally accepted that an increased nutrient supply will not improve plant growth when the nutrient is already present in sufficient amounts in the soil and when the drought or salt stress is severe. A better understanding of the role of mineral nutrients in plant resistance to drought and salinity will contribute to an improved fertilizer management in arid and semi-arid areas and in regions suffering from temporary drought. This paper reviews the current state of knowledge on plant nutrition under drought and salinity conditions. Specific topics include: (1) the effects of drought and salt stress on nutrient availability, uptake, transport, and accumulation in plants, (2) the interactions between nutrient supply and drought- or salt-stress response, and (3) means to increase nutrient availability under drought and salinity by breeding and molecular approaches. Trockenstress und Salzstress , Vergleich der Auswirkungen auf die mineralische Ernährung von Pflanzen Eine Zunahme von Trockenperioden in vielen Ländern der Welt und assoziierte Probleme der Versalzung in bewässerten Gebieten führen häufig zu gleichzeitigem Auftreten von Trockenheit und Salinität. Gegenwärtig sind weltweit ungefähr 50 % aller Bewässerungsflächen durch Salinität beeinträchtigt. Nährstoffstörungen bei Trocken- und Salzstress beeinträchtigen die Verfügbarkeit, den Transport und die Verteilung von Nährelementen in der Pflanze und reduzieren somit das Pflanzenwachstum. Trocken- und Salzstress können sich jedoch unterschiedlich auf die Nährstoffversorgung der Pflanzen auswirken. Salinität kann aufgrund der Konkurrenz zwischen Na+ bzw. Cl, und Nährelementen wie K+, Ca2+ und NO Nährstoffmängel oder -ungleichgewichte in den Pflanzen verursachen. Trockenstress kann sowohl die Nährstoffaufnahme als auch den akropetalen Transport einiger Elemente beeinträchtigen. Trotz kontroverser Schlussfolgerungen in der Literatur hinsichtlich der Wechselbeziehungen von Nährstoffangebot und Trocken- bzw. Salzstress auf das Pflanzenwachstum ist allgemein akzeptiert, dass Nährstoffzufuhr das Pflanzenwachstum nicht verbessert, wenn ausreichend Nährstoffe im Boden verfügbar sind oder bei stark ausgeprägter Trockenheit oder Salinität. Ein besseres Verständnis der Rolle von Mineralstoffen in der Toleranz von Pflanzen gegenüber Trocken- oder Salzstress dürfte gerade in ariden und semi-ariden Gebieten sowie in Regionen, die unter periodischer Trockenheit leiden, zu verbesserten Düngestrategien beitragen. In der vorliegenden Arbeit wird der gegenwärtige Kenntnisstand der mineralischen Ernährung bei Trockenheit und Salinität diskutiert. Schwerpunkte der Betrachtungen sind (1) die Auswirkungen von Trockenheit und Salzstress auf die Verfügbarkeit, die Aufnahme, den Transport und die Anreicherung von Nährelementen in der Pflanze, (2) Wechselbeziehungen zwischen dem Nährstoffangebot und Trockenheit oder Salinität sowie (3) Maßnahmen zur Verbesserung der Nährstoffverfügbarkeit bei Trockenheit und Salzstress mittels züchterischer und molekularbiologischer Ansätze. [source]

Farmers' perception of treated paper mill effluent irrigation

LAND DEGRADATION AND DEVELOPMENT, Issue 3 2010
P. N. Rekha
Abstract The utilization of treated paper mill effluents for irrigation offers many benefits such as conservation of water resources, conversion of barren land into irrigated area, addition of nutrients to the soil and plant and above all the reduction of pollution of inland water bodies. However, the utility of this effluent irrigation programme depends mainly on farmers' acceptability, adoption and management of the scheme. Knowledge about the farmers' perception is thus very much imperative for further advocacy of the effluent irrigation programme. The determinants of farmers' perception of treated paper mill effluent irrigation is a pre-requisite for the formulation of better programmes and strategies for the support of an unobstructed adoption and for the long-term sustainability of effluent irrigation schemes. The present study was conducted to assess the farmers' perception and the determinants that influence the adoption of treated paper mill effluent irrigation by interviewing a random sample of 120 farmers, using a well-structured interview schedule in paper mill effluent irrigated area in Tamil Nadu in India. The study revealed that there exists positive significant correlation between the perception and the characteristics of the farmers viz. educational status, farm size, annual income, mass media exposure, innovativeness and risk orientation. The response analysis of the perception revealed that treated paper mill effluent as alternative assured supply of irrigation water, conversion of elevated dry lands to irrigated land, changing of cropping pattern to sugarcane, increase in socioeconomic status of the farmers, incentives and technical inputs by the paper mill authorities and above all farmers' participation in planning, implementation and management of the effluent irrigation schemes influenced the farmers to form positive perception. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Impact of irrigation on malaria in Africa: paddies paradox

MEDICAL AND VETERINARY ENTOMOLOGY, Issue 1 2001
J. N. Ijumba
Summary The high population growth rate of the African continent has led to an increased demand for food and is in danger of outstripping agricultural production. In order to meet this need, many governments have sought ways of improving food production by initiating large-scale irrigation projects, involving reclamation of arid and semi-arid areas for the cultivation of crops. Although crop irrigation promises one solution to alleviating hunger and encourages economic growth, irrigation has often been blamed for aggravating disease in local communities. Malaria is one of the major tropical diseases associated with irrigation schemes, and changes in the transmission pattern of this disease following irrigation development have been a perennial subject of debate. It has often been assumed that high numbers of malaria vector Anopheles mosquitoes (Diptera: Culicidae) resulting from irrigation schemes lead inevitably to increased malaria in local communities. However, recent studies in Africa have revealed a more complex picture. Increased numbers of vectors following irrigation can lead to increased malaria in areas of unstable transmission, where people have little or no immunity to malaria parasites, such as the African highlands and desert fringes. But for most of sub-Saharan Africa, where malaria is stable, the introduction of crop irrigation has little impact on malaria transmission. Indeed, there is growing evidence that for many sites there is less malaria in irrigated communities than surrounding areas. The explanation for this finding is still unresolved but, in some cases at least, can be attributed to displacement of the most endophilic and anthropophilic malaria vector Anopheles funestus Giles by An. arabiensis Patton with lower vectorial capacity, as the latter thrives more than the former in ricefields. Similarly, among members of the An. gambiae complex, some cytotypes of An. gambiae sensu stricto are more vectorial than others. For example, the Mopti form has high vectorial capacity and breeds perennially in irrigated sites, whereas the savanna form is often sympatric but more seasonal. Also we suggest that many communities near irrigation schemes benefit from the greater wealth created by these schemes. Consequently irrigation communities often have greater use of bednets, better access to improved healthcare and receive fewer infective bites compared with those outside such development schemes. Thus, in most cases, irrigation schemes in Africa do not appear to increase malaria risk, except in areas of unstable transmission. However, developers should take the opportunity to improve health-care facilities for local communities when planning irrigation schemes wherever they occur. [source]