Figure 8: Percentage of country populations that will be water stressed in the future Source: Rost et al. (2009) Water limitation of crop production in the absence of irrigation, i.e. ratio of NPP (INO simulation) and NPP (OPT simulation), 1971–2000 averages. The lower the ratio the stronger the water limiation. Available at: http://iopscience.iop.org/1748-9326/4/4/044002/fulltext
greening their agricultural practices, rather than seeking widespread expansion of arable land.
The agriculture sector is the largest consumer of fresh water, accounting for 70 per cent of global use, including rainfall run-off. A majority of crop lands are exclusively rain-fed, and only 24 per cent of arable land is cultivated with the help of irrigation from flowing surface waters or groundwater aquifers (Portmann et al. 2009). This distinction is important because irrigated fields are much more productive and produce nearly a third of all agricultural output (Falkenmark and Rockstrom 2004).
The increasing disruption of historical rainfall patterns experienced in many areas of the world is a cause for great concern since rain-fed farming is the dominant form of agriculture. The Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report concluded that many observed changes in extremes, such as more frequent, heavy precipitation events and longer, more intense droughts, are consistent with warming of the climate system (IPCC 2007a). While affecting rain-fed agriculture, precipitation changes also adversely affect the recharge rates of aquifers and watersheds. The continued worsening of water-stress conditions suggests that efforts to increase the use of irrigation will gradually increase agricultural production costs. Clearly, practices that increase water-use efficiencies are required to alleviate this trend.
Figure 8 shows projections for global water stress in the future. The figure also underscores the need for increased coordination in water use nationally and across borders. In this context, the Mekong River Commission, which coordinates the watershed development plans of member states, is one of several promising supra-national river basin initiatives.
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Limited availability of mineral inputs Industrial farming practices are dependent on inorganic fertilisers. In turn, the production and prices of these depend on the availability of fossil fuels, minerals and petro-chemicals. In this context, the demand for two major minerals – potassium and phosphorous – used
Box 2: Opportunities for improved sanitation systems and organic nutrient recycling
There is a critical need to recover and recycle nutrients from organic waste streams and use them as productive inputs of organic fertiliser. Enormous quantities of valuable organic nutrients could be recovered from intensive livestock farming; food processing sites; municipal green wastes; and human sewage wastes in both rural and urban communities. It is particularly important to maximise the recovery of phosphorous nutrients from organic wastes; as a mineral, phosphate is essential to agricultural productivity and it has been estimated that economically recoverable global reserves may be depleted in 100 years (Cordell et al. 2010). Technologies are under development that would eliminate pathogens and other toxic elements from these waste streams and recover commercial quantities of phosphorus (Frear et al. 2010). It is expected that the rising costs of inorganic fertilisers will help accelerate research and commercialisation of such organic nutrient-recovery technologies.