"Irrigation is the prime means of intensification and will remain a keystone of food security policies in the face of climatic variability."
The FAO has come out with a 200-page PDF report titled "Climate Change, Water, and Food Security." The comprehensive report focuses on water management as climate change conditions evolve. The focus is on irrigated systems that currently produce roughly 40 percent of global food output from 20 percent of the global stock of cultivated land, and withdraw more than 70 percent of the volume of water used for human benefit.
The following bullets are of note from the report:
- Reductions in river runoff and aquifer recharge are expected in the Mediterranean basin and in the semi-arid areas of the Americas, Australia and southern Africa, affecting water availability in regions that are already water-stressed.
- In Asia, the large contiguous areas of irrigated land that rely on snowmelt and high mountain glaciers for water will be affected by changes in runoff patterns, while highly populated deltas are at risk from a combination of reduced inflows, increased salinity and rising sea levels.
- Irrigation provides approximately 40 percent of the world’s food, including most of its horticultural output, from an estimated 20 percent of agricultural land, or about 300 million ha worldwide.
- Aquifers are depleted in many parts of the world where they are most important – China, India and the United States - sometimes facilitated by perverse incentives of subsidized energy and support prices for irrigated products.
- Future global food demand is expected to increase by some 70% by 2050, but will approximately double for developing countries. All other things being equal (that is a world without climate change), the amount of water withdrawn by irrigated agriculture will need to increase by 11% to match the demand for biomass production.
- The world has a large stock of under-performing canal irrigation infrastructure, and a vibrant groundwater sector that is competitively depleting its own lifeblood.
- Mean temperatures are expected to rise at a faster rate in the upper latitudes, with slower rates in equatorial regions.
- Water-scarce areas of the world will generally become drier and hotter.
- Increased atmospheric temperature will extend the length of the growing season in the northern temperate zones, but will reduce it almost everywhere else.
- Worldwide cereal yields are expected to decline by 5 percent for a 2 ˚C rise in temperature and by 10 percent for a rise of 4 ˚C.
- Cereal production is expected to fall by between 9 and 11 percent in the developing country regions and Australia/New Zealand, but it is expected to increase by as much as 11 percent in the developed countries, including Russia, thereby reinforcing existing disparities in food production.
- However, the temperature increases that open up ‘new’ growing seasons for cereals in the higher latitudes and the associated increases in evapotranspiration rates will increase the demand for irrigation.
- Where irrigation is already commonplace and rainfall declines, such as in southern Europe, crop water productivity will have to increase or crop areas will contract.
- Rainfed farming will become more precarious in the mid and low latitudes, while productivity may rise for a time in the higher latitudes (notably North America and northern Europe).
- Large-scale land-use change is expected on all continents.
- In rainfed systems, if potential evaporation rates increase, available root zone moisture content will be more rapidly depleted, requiring either shorter season crop varieties or acceptance of lower yields and more frequent crop failure.
- Agriculture accounts for 69 percent of all water withdrawals in the world, but offers the lowest economic return per unit of water.
Ironically, genetically modified crops already point the way to farming systems with low or zero reliance on pesticides, and nitrogen-fixing cereals may one day become a reality. In the meantime, it will be important to be as efficient as possible in the pursuit of ‘industrial’ agriculture.and this . . .
Yields are estimated to fall uniformly in the tropics due to temperature rise but higher productivity is expected in the higher latitudes with longer season growth, more optimal growing conditions, and the probable development of new lands. As temperature rises further at higher latitudes, productivity may then decrease in the longer term (USDA, 2008), and improved potential productivity may not be realized, as conditions for pests and diseases will become more favourable. The mid-latitudes will suffer from declining yields because temperature change and areas will decline as a result of reduced water availability – for irrigation and rainfed farming in the Mediterranean, southern Europe, mid-west United States and the semi-arid to arid sub-tropics.and . . .
A recent report on adaptation in agriculture by the World Bank notes that agricultural systems will shift at the margins of their current location and condition. This will result in loss of extensive rangeland; conversion of marginal arable land to rangeland; and a change to production systems with greater temperature or drought tolerance. For example, replacement of maize with sorghum and millet; and conversion of wet rice to dry-footed crops or upland rice in tropical areas impacted by declining water availability or increased evaporation (Padgham, 2009).
and . . .
The total land area across the world amounts to around 13 billion ha, of which 1.5 billion ha is cultivated (12 percent) and a further 27 percent is managed as pastureland for livestock production. Between 1960 and 2000, the globe’s cultivated area increased by 13 percent, while population more than doubled. Of the 510,000 km3 of water that falls on the earth each year, only 110,000 km3 occurs over land, generating a runoff of roughly 44,000 km3 (40 percent). It is estimated that total water use in crop production (evapotranspiration) amounted to 7130 km3 in 2000 and is likely to rise to between 12,000 and 13,500 km3 by 2050 (de Fraiture et al., 2005). An overall expansion in cropped area of 29 percent is forecast to 2050, with rainfed areas increasing from 549.812 million in 1998 to 698.743 million ha (27 percent). Irrigated area is forecast to grow by 33 percent, from 242 182 million ha to 318 million ha over the same period (Bruinsma, 2009).
~~~~~Irrigation is commonly found in major deltas in South, East and Southeast Asia, and their vulnerability in terms of displaced people as a result of current trends to 2050 is shown in the following graphic:
extreme: >1 million
high: 1 million to 50 000
medium: 50 000 to 5 000
[Climate Change 2007: Impacts, Adaptation and Vulnerability. Working Group II Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Figure TS.8. Cambridge University Press.]
There is much, much more at the source.
[source: 200 page pdf file here]