By 2050, climate change will increase extreme drought, especially in the subtropics and low- and mid-latitudes. Increased water stress will impact land areas twice the size of those areas that will experience decreased water stress.

Bates et al., 2008

Adapted from IWMI, Aditya Sood and Vladimir Smakhtin

Extra facts

  • Changes in water quantity and quality due to climate change are expected to reduce the food security and increase the vulnerability of poor rural farmers, especially in the arid and semi-arid tropics and in Asian and African mega-deltas.
  • Increased precipitation intensity and variability are projected to increase the risk of flooding. The proportion of land surface experiencing extreme drought at any time is also projected to increase, especially in the subtropics and the low and mid-latitudes (Bates et al. 2008)
  • Climate model simulations for the 21st century consistently project precipitation increases in high latitudes (very likely) and parts of the tropics, and decreases in some subtropical and lower mid-latitude regions (Bates et al. 2008)
  • In the 21st century, annual average river runoff and water availability may increase in some wet tropical areas and decrease in some dry regions at mid-latitudes and in the dry tropics (Thornton et al. 2012).
  • Water supplies from inland glaciers and snow cover are projected to decline in the 21st century, continuing a 20th-century trend. This will reduce water availability during warm and dry periods—when irrigation is most needed—in regions supplied by melt water from major mountain ranges. This area is home to one-sixth of the world’s population—most of whom are poor (Bates et al. 2008).
  • Greater interannual rainfall variability may be associated with lower GDP, particularly in poor countries (Brown and Lall 2006 IN Kahn and Hanjra 2009).
  • Sea level rise is projected to extend areas of groundwater and estuary salinization, resulting in a decrease of freshwater availability for humans and ecosystems in coastal areas (Thornton et al. 2012).
  • By 2025, 15–20 million hectares of irrigated rice will experience some degree of water scarcity (Bouman et al. 2007).
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Methods, caveats and issues

  • Average long-term surface wetness and temperature (climate normals) and interannual climate variance impact farm cropland and revenue (Mendelsohn et al. 2007a), but interannual climate variability is much more important than climate normals (Easterling et al. 2000).
  • There is a larger degree of uncertainty about the future impacts of climate change on water resources than about climate variability (Kahn and Hanjra 2009: 130). For the 21st century, climate models consistently project mean precipitation increases in parts of the tropics and decreases in some subtropical and lower mid-latitude regions. Outside these areas, the direction and magnitude of projected changes remains very uncertain (Thornton et al. 2012).
  • It is important to differentiate between glacier melt and snowmelt sources, and to assess these at the basin scale. Glacier contributions to river flow in the large monsoon area basins may not be very significant. Large high-altitude glacier systems in basins such as the Indus, which provide water for agriculture in most of Pakistan, may not be particularly sensitive to the temperature increases projected for the 21st century (Thornton et al. 2012).
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  • Bates BC, Kundzewicz ZM, Wu S, Palutikof JP, eds. 2008. Climate change and water. Technical paper for the Intergovernmental Panel on Climate Change. Geneva: Intergovernmental Panel on Climate Change. (Available from
  • Bouman BAM, Humphreys E, Tuong TP, Barker R. 2007. Rice and water. Advances in Agronomy 92:187–237.
  • Thornton P, Cramer L. 2012. Impacts of climate change on the agricultural and aquatic systems and natural resources within the CGIAR’s mandate. CCAFS Working Paper 23. Copenhagen: CGIAR Research Program on Climate Change, Agriculture and Food Security. (Available from
  • Khan S, Hanjra MA. 2009. Footprints of water and energy inputs in food production—global perspectives. Food Policy 34:130–140. (Available from
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