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  • Home > Water, Food and Energy Nexus - Updated: 27-04-2009 3:07 pm

    By far the largest user of fresh water is agriculture, which now accounts for around three-quarters of global water consumption. If, as is almost certain, the population increases by 65 per cent over the next 50 years, around 70 per cent of this future world population will face water shortages and 16 per cent will have insufficient water to grow their basic food requirement.


    The necessary increases in food production cannot be achieved without higher productivity on existing land and with existing water resources. A central question for HELP is therefore "what is the scope for increasing the efficiency with which water is used in agriculture?"

    Although irrigation is often proposed as the way to achieve higher productivity per unit area of land, it increases the pressure on freshwater resources. Further, because irrigated agriculture only provides about a third of the world’s food, a relatively large increase in production would be required. On the other hand, increasing the efficiency of rain-fed agriculture would both increase food production and also reduce the demand on freshwater resources. Most global assessments of future food production ignore the possibility of increasing rain-fed food production per unit area. However, in regions such as sub-Saharan Africa where population growth is very high, most (>90 per cent) food comes from rain-fed agriculture, and this is likely to remain the case for the foreseeable future. It is therefore essential to increase water-use efficiency in rain-fed, as well as in irrigated, agriculture.


    Food and water policy

    Five key policy issues are identified in respect of water and food:


    • the extent of future additional irrigation, and the degree of predicted food shortage if irrigation is not expanded; and the predicted downstream water shortages if irrigation is expanded;
    • national food security versus international trade in food;
    • increases in total food productivity (both rain-fed and irrigated);
    • closing the yield gap, rather than extending the yield frontier (focusing on reducing below-average variations in within-farm yields, rather than increasing the average yield per unit of input);
    • the transition of irrigation organisations to service businesses, and the transfer of the management of smaller systems to users.


    Food and water management


    We can only improve agricultural water management and at the same time increase food production by improving water-use efficiency. This is true for irrigated as well as rain-fed agriculture. It means producing the same or a larger amount of food with less water. While improving water-use efficiency relates mainly to water quantity, improving or maintaining water quality is also a central task for agricultural water management. While the increase of food production is the most pressing issue in many countries, the maintenance and improvement of water quality is of prime concern in others.We can improve water-use efficiency through:

    • modifications in agricultural tillage practices
    • changes in crop type
    • reduction of soil evaporation
    • optimised crop selection
    • technological improvements
    • reduction of transportation loss
    • pricing policy
    Water-use efficiency must be measured with respect to the whole catchment, taking into account possible reuse of water. While the reduction of unproductive evaporation loss is a central goal of improving water-use efficiency,reduction in groundwater recharge might be undesirable for downstream withdrawals. Thus water management has carefully to distinguish different water pathways within the catchment and must account for interactions and feedbacks within the system. To secure future food and water supplies, we need to take several interventions and actions, as follows:
    • 1. reform of institutional and regulatory actions;
    • 2. technology advancement;
    • 3. environmental and ecological preservation;
    • 4. social and cultural amendments;
    • 5. recognition of urban and rural demands;
    • 6. recognition of demand and participatory management approaches;
    • 7. building capacity and technology transfer.


    The hydrological sciences contribution


    The technical basis for improving agricultural water-use efficiency is to increase the total amount of the water made available to plants, and/or to increase the efficiency with which transpired water produces biomass. The main ways in which the former can be achieved is to improve infiltration(that is, reduce surface runoff), reduce direct evaporation of water from the soil (or irrigation water) and reduce drainage. We know some of the basic techniques for reducing surface runoff, soil evaporation and drainage, but the suitability and net effect of a particular approach in a given environment require further study.

    We can achieve another form of efficiency improvement by fixing more carbon per unit of water transpired. This "transpiration efficiency" varies with crop type and atmospheric humidity, with higher efficiencies in more humid environments. In principle, therefore, more biomass could be produced using the same amount of water by selecting species with high transpiration efficiencies or by growing plants in more humid air. The latter could be done on a macro scale, that is, by growing plants and/or using irrigation water at times, or in places, where air humidity is high. There is also some scope for microclimate manipulation in semi-arid regions where the relative humidity around crops can be increased using an over-storey of trees. Again the scope for improving transpiration efficiency has been identified, but there is a need for systematic study of which options are likely to work in particular environments. It should also be noted that too much water can lead to waterlogging and salinity problems.

    In brief, the main scientific question about food and water that requires research is:

      how can the efficiency with which water is used in agriculture be improved and how do the need, scope and methods for achieving this vary regionally and locally?
      Subsidiary issues for study include:
      • the most appropriate techniques for reducing water losses from agricultural fields due to surface runoff, soil evaporation and drainage;
      • how much water could be saved by improving transpiration, and what techniques can be used to do this;
      • how much water efficiency could be improved by using different crops and/or crop mixtures;
      • the relative savings to be made in rain-fed and irrigated agriculture, and potential for the complementary use of water between the two;
      • whether significant efficiency gains can be made through assessing the way water can be used in different places and at different times across an entire catchment;
      • the downstream impacts of increasing water-use efficiency in agricultural areas;
      • the reasons local farmers do not adapt apparently straightforward technologies for improving water-use efficiency.


    There is much scope for improving water-use efficiency in agriculture, but appropriate solutions need to be developed for particular physical, social and economic conditions. We need to increase efforts to introduce technical innovations to the social, political and institutional structures that can encourage farmers to adopt the improvements. If this was achieved, then more areas of the world would be able to produce the food they need for their current and future populations.

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