Workshop 1 - Water management for sustainable agriculture

Abstract

WATER MANAGEMENT FOR SUSTAINABLE AGRICULTURE IN THE MEDITERRANEAN AREA.

M. Jan HOEKS - Head of Division of Water Management - DLO Winand Staring Centre - THE NETHERLANDS

The availability of water of good quality is becoming a problem in the Mediterranean area. The ever-growing demand for drinking water and irrigation water is mainly caused by the increase in population and the expansion of irrigated areas. The water resources, however, will probably not increase, in fact a decrease is perhaps more realistic in view of the expected climatic changes for the area. This unbalance in demand and supply of water already leads to overexploitation of groundwater resources, resulting in lowering of groundwater levels and reduction of natural river flows.

Careful and efficient use of irrigation water and the reuse of drainage water and waste water will be needed to save as much water as possible. Modern techniques and management practices must be introduced to raise the efficiency of irrigation and to prevent soil degradation and salinization problems at the regional level and farm level. Soil erosion should be controlled by proper agricultural practices to prevent land degradation, loss of fertile soil, and loss of water by runoff ultimately leading to desertification.

Research projects, a.o. in Egypt, Spain, India, Argentina, but also in the Netherlands, show that monitoring and planning tools can be very useful to evaluate the effects of different land and water management practices on irrigation efficiency. Monitoring is very important to collect relevant information on irrigation systems , e.g. the water requirements of different crops in the irrigation area, the water distribution via primary, secondary and tertiary irrigation canals, and the actual crop development. In addition to ground observations, remote sensing (RS) data appear to be very useful to collect information on the area of irrigated land, the areal distribution of crops, the vegetation dynamics and the actual evapotranspiration. In the framework of climatic research RS images are used to gain information on land surface hydrological processes for vast heterogeneous terrains. Furthermore, time series of RS images make it also possible to monitor long term changes in (irrigated) land use, vegetation development and climate changes.

With respect to water management planning at a regional or national level planning tools are needed. The SIWARE-model appeared to be an effective tool for evaluation of water management plans for the Nile Delta. Combined with remote sensing data and other geographical data systems, models are useful tools to predict future developments, to optimize water distribution and reuse of drainage water, and to evaluate landuse changes and other cropping systems e.g. with water saving crops or perhaps also salt tolerant crops.

For optimal use of the limited water resources in the Mediterranean region much attention should be given to the prevention of water pollution. In addition to point sources (sewage, industrial waste water) also diffuse pollution is a problem; for instance the emission of pesticides from agriculture threatens water quality and thus public health. Dutch research on this topic indicates that pesticide emissions may be controlled by setting up information systems on use and application of pesticides (comparable to the Dutch ISBEST) and using simulation models to predict emissions into the environment. Such information systems, when linked to water management models, provide the opportunity to evaluate alternative measures for improvement of water quality.

Participation of farmers and water user associations is needed, i) to raise the efficiency of on-farm irrigation, ii) to make them aware of the scarcity of water and the need for reduction of water losses, iii) to prevent water pollution. Decision support systems, e.g. the SWAP-model, for on-farm irrigation scheduling together with water pricing can be effective tools to save water. For the near future, socio-economic aspects should be introduced in such decision support systems.

Research on evaporation in desert areas in North Africa has indicated that the renewable groundwater resources are probably larger than expected. The evaporation of groundwater in deep depressions (e.g. Quatara depression) as derived from satellite data appeared to be larger than was expected on the basis of groundwater modelling studies. In these studies the viscosity of water in deep aquifers was not corrected for the prevailing high temperatures, which leads to an underestimate of groundwater flows. Therefore renewed research on groundwater reserves in North Africa seems very promising.