Interaction between water supply and demand in two collective irrigation schemes in North-East Brazil

Over the past three decades, public irrigation schemes have been exposed to a process of management transfer from the central government and the funding agencies to local entities such as water users' associations and districts. However, this management transfer has been in many cases poorly implemented. Frequently reported problems are: inappropriate design; poorly specified management functions; ineffective accountability; unclear ownership of the collective infrastructure, and a lack of support services for achieving the transfer of management with success. In the Petrolina-Juazeiro region in the Northeast of Brazil, the CODEVASF (Company for the Development of the Valleys of the São Francisco and the Parnaiba Rivers) has started to gradually transfer the management of public irrigation schemes to districts or local management entities. The districts are responsible for every day management, but they also need to make strategic decisions that affect the sustainability (technical, financial, socio-economic, environmental) of the irrigation schemes in the long run. This dissertation was set up in the irrigation projects of Mandacaru and Maniçoba, to analyse the scheme management by the main internal stakeholders (scheme manager versus farmers), as well as to support them to solve problems and to plan ahead. The research focused on the interaction between the scheme manager's water supply and the farmers' water demand, since it is the central function inside the irrigation scheme.[...] A simulation model was developed to support the stakeholders' reflections on alternative plans of the water supply and demand. The modelling of the collective water supply is limited to its main infrastructure and organizational parameters. The collective water demand is modelled by using a farm typology that gives a simplified representation of the diversity of the farms in the irrigation scheme, as well as their water demands. The main output of the model is the coverage of the water demand by the water supply at scheme level. The aim of the modelling approach was to provide support to stakeholders so that they can simulate and evaluate prospective scenarios of the water demand and alternative plans of the water supply, for example the possibility to increase the water supply by organizing water delivery to farmers at night [...] Further analysis of the real contribution of this type of decision support methods in the stakeholders' learning process of irrigation management needs to be undertaken on other case studies, so as to evaluate their real interest and transferability to other specific situations of irrigation scheme management. (Résumé d'auteur