Watering cows in India. Competetion for water between different groups of users is on the increase.
The scarcity of water for use by agriculture is posing a challenge to food production in a number of areas, FAO research shows. Eleven countries are currently using more than 40 percent of their water resources for irrigation each year, a threshold that is considered crucial, another eight are withdrawing 20 percent of their water resources annual, indicating substantial pressure and impending water scarcity.
Additionally, in many places, “excessively optimistic” estimates of available surface water resources and over-allocation of water rights can mean serious shortages when the weather takes a turn for the worse and droughts occur.
For example, in Australia, average inflows to the Murray-Darling river system during 2001/2–2009 were only 33% of the average over the previous 100 years – which was the basis for the existing system of allocation. The Colorado River in the southwestern United States is another case of over-allocated water. Future climate change is likely to further invalidate the hydrological assumptions on which current rights were issued.
Climate change adds additional pressure
Climate change is expected to place a number of additional pressures on the availability of water for food production.
Projections show a general reduction in precipitation in semi-arid areas, an increase in precipitation in temperate zones, higher variability in rainfall distribution, an increase in the frequency of extreme events, and an increase in temperature. These effects will have a particular impact on tropical and sub-tropical agriculture.
A severe reduction in river runoff and aquifer recharge is expected to occur in the entire Mediterranean basin, as well as the semi-arid areas of southern Africa, Australia and the Americas.
A combination of reduced river base flows, flooding and rising sea levels are predicted to affect highly productive irrigated systems dependent upon glacier melt (like the Punjab and Colorado) and lowland deltas (such as the Indus, Nile, and Brahmaputra-Ganges-Meghna – the world’s most densely populated delta).
In the semi-arid tropics, where increased occurrence of droughts and floods is predicted, climate change is expected to affect the rural poor in particular, by reducing crop and livestock yields.
Generally, more frequent and severe droughts and floods will hurt local production, especially in subsistence sectors at low latitudes and in key food insecure areas dominated by rainfed agriculture.
