Climate change will have major impacts on the availability of water for growing food and on crop productivity in the decades to come, warns a new FAO report.
Climate Change, Water, and Food Security is a comprehensive survey of existing scientific knowledge on the anticipated consequences of climate change for water use in agriculture. These include reductions in river runoff and aquifer recharges in the Mediterranean and the semi-arid areas of the Americas, Australia and southern Africa -- regions that are already water-stressed. In Asia, large areas of irrigated land that rely on snowmelt and mountain glaciers for water will also be affected, while heavily populated river deltas are at risk from a combination of reduced water flows, increased salinity, and rising sea levels.
Additional impacts described in the report
An acceleration of the world's hydrological cycle is anticipated as rising temperatures increase the rate of evaporation from land and sea. Rainfall will increase in the tropics and higher latitudes, but decrease in already dry semi-arid to mid-arid latitudes and in the interior of large continents. A greater frequency in droughts and floods will need to be planned for but already, water scarce areas of the world are expected to become drier and hotter. Even though estimates of groundwater recharge under climate change cannot be made with any certainty, the increasing frequency of drought can be expected to encourage further development of available groundwater to buffer the production risk for farmers. And the loss of glaciers - which support around 40 percent of the world's irrigation -- will eventually impact the amount of surface water available for agriculture in key producing basins.
Increased temperatures will lengthen the growing season in northern temperate zones but will reduce the length almost everywhere else. Coupled with increased rates of evapotranspiration this will cause the yield potential and water productivity of crops to decline. "Both the livelihoods of rural communities as well as the food security of city populations are at risk," said FAO Assistant Director General for Natural Resources, Alexander Mueller. "But the rural poor, who are the most vulnerable, are likely to be disproportionately affected."
Responding to the challenge
FAO's report also looks at actions that can be taken by national policymakers, regional and local watershed authorities, and individual farmers to respond to these new challenges.
One key area requiring attention is improving the ability of countries to implement effective systems for ‘water accounting' - the thorough measurement of water supplies, transfers, and transactions in order to inform decisions about how water resources can be managed and used under increasing variability.
"Water accounting in most developing countries is very limited, and allocation procedures are non existent, ad hoc, or poorly developed," the report says. "Helping developing countries acquire good water accounting practices and developing robust and flexible water allocations systems will be a first priority."
At the farm level, growers can change their cropping patterns to allow earlier or later planting, reducing their water use and optimizing irrigation. Yields and productivity can be improved by shifting to soil moisture conservation practices, including zero- and minimum tillage. Planting deep-rooted crops would allow farmers to better exploit available soil moisture.
Mixed agroforestry systems also hold promise. These systems both sequester carbon and also offer additional benefits such as shade that reduces ground temperatures and evaporation, added wind protection, and improved soil conservation and water retention. However, FAO's report also stresses that small-scale producers in developing countries will face an uphill struggle in adopting such strategies. "Farm size and access to capital set the limits for the scope and extent of adaptation and change at farm level," it warns, noting that already today many developing world farms produce yields far below their agro-climatic potential.
Zooming in on hotspots
FAO also warns that far too little is known about how climate change impacts on water for agriculture will play out at the regional and sub-regional level, and where farmers will be most at risk. "Greater precision and focus is needed to understand the nature, scope and location of climate change impacts on developing country water resources for agriculture," the report says, adding: "Mapping vulnerability is a key task at national and regional levels."