The world currently produces enough food to feed itself and is expected to continue doing so until 2050 when populations are predicted to stabilize at around 10 billion. Still, meeting predicted global food security needs will require considerable effort to increase food output. At the same time, there will be additional demands to solve hunger problems brought about by distribution and access deficiencies in particular regions and for particular groups of people in those regions, even in the midst of global food abundance. A large part of the solution to global and regional food problems is likely to be found through irrigated agriculture.

However, the World’s population has doubled from 3 billion in 1960 to 6 billion in 2000. The nutritional demands have also risen from 2,255 kilocalories per person per day (kcal/cap/day) in 1961 to around 2,800 kcal/cap/day in 1998 (Webb, 2002, 2001). Yet the cropland area increase has been only modest from 1.36 billion hectares in 1960  to 1.47 billion hectares in 1990 (see Ramnakutty, and Foley, 1999, 1998). Based on various estimates, it has remained around 1.5-1.8 billion hectares at the end of the millennium (World Resources 1992-1999, Ramanakutty and Foley, 1988), of which about 16-18 percent is irrigated (FAO, 2001). Irrigated areas are also increasing at much slower phase of about 1.3 percent per year at present when compared to 2.6 to 3 percent during the peak irrigation era of 1960-1980 (e.g., see in Postel, 1999). Given these facts, how does the World feed itself?. It is widely accepted that cultivation intensities (more than one crop a year especially through irrigation) and increased gain yields have been meeting the World’s food demand in recent decades. But what is the extent of the increase in cultivation intensities in irrigated lands?. There are no estimates of this. What are the spatial distributions of these irrigated areas in the World?. Further, with overwhelming proportion of all the water use is for irrigation, an accurate estimate of intensities of irrigated lands will be crucial to determine consumptive use of water by crops, and cropland dynamics over space and time. The need to set a platform for consistent future estimates of irrigated areas and related information can not be overemphasized in a World that will need to feed ballooning population in a scarce Land and water resources.

Irrigation is widely thought to provide 40% of the world’s food from around 17% of the cultivated area, and has been an instrumental factor in the success of the ‘Green Revolution’ in meeting food needs over the past 40 years, particularly for staple grains. These successes have come at significant environmental costs through river regulation and land and water degradation from inputs to intensive agriculture. For example, irrigation typically consumes over 70% of diverted water resources in Asia, where irrigation development has been mainly concentrated. Key questions concerning the sector include:

o         How much irrigation do we have now?

o         How much do we need in the future?

o         How much do we want in the future to achieve a sustainable balance with the environment?

o         How much water does it require and will this be available?

Previous efforts to quantify the amount of irrigation in the world have relied on secondary statistics, which in many instances systematically over or under-estimate actual cropped irrigated area. For example, some 60% of irrigation in India now is practiced using groundwater, most of which is privately developed and not necessarily recorded in government statistics. Irrigated areas of the World in the past have been accounted primarily using the Government statistics and place global equipped area for irrigation between 250-280 million Ha. These estimates use a combination of statistics, existing GIS and other techniques to indicate the distribution of irrigated areas in different parts of the world. The best known of these is the Food and Agricultural Organization of the United Nations and the University of Frankfurt (FAO\UF) derived global map of irrigated areas (Siebert et al., 2006, and Siebert et al., 2005).

While these being excellent efforts, there is still substantial room for improvement in estimates, and this is the impetus for the IWMI global irrigated area map (GIAM). The IWMI GIAM is derived from a great variety of remote sensed data at different geographical and time scales, in the expectation that the vegetation dynamics revealed will:

1)       define more precisely the actual area and precise spatial distribution of irrigation, and

2)       elaborate the extent of multiple cropping over a year, particularly in Asia, where two or three crops may be planted in one year. This is especially useful since cropping intensities are not accurately known or recorded in secondary statistics.

The major finding of the IWMI GIAM analysis is the reporting of irrigated areas with and without intensity.

The annualized irrigated areas (AIA) considers intensity of irrigation and is equivalent of gross cropped area under irrigation. The AIA was determined to be 467 million ha. This very significantly exceeds the estimates of equipped area of FAO\UF at 274 Mha (Siebert et al. 2006, Siebert et al. 2005) and others (257 to 280 million ha) (van Schilfgaarde, 1994, Siebert, S., Döll, P., Hoogeveen, J., 2002), due to the extent of multiple cropping and private and community developed irrigation. The area estimates in the map are derived for each characteristic agricultural systems around the world (e.g. long season winter sown cereals in the northern hemisphere; triple rice cropping in SE Asia; wet monsoon season (Kharif) and dry winter (rabi) systems in the Indian sub-continent).  We have summarized the statistics for three notional cropping seasons running from June-September (including single long season crops harvested in this period), October to February, and from March to May[1]. The estimated areas are 252, 174 and 41 million Hectares, respectively.

The total area available for irrigation (TAAI) does not consider intensity of irrigation and is equivalent of net irrigated areas (NIA) which is determined to be 399 Mha. The figure of 257 million Hectares equates to equipped area in FAO and other estimates (257 Mha to 280 Mha), and the development of global irrigated area is summarized in the chart, with and without estimates of cropping intensity.

Historical development of global irrigated area, with and without cropping intensity expressed in Million Hectares.

It is useful to present the gross irrigated area according to seasonal breakdown that reflects cropping intensity as presented in this study (see next paragraph and the documentation for details). However, at global level, further refinement maybe necessary in order to account for varying seasonality by taking more precise cropping calendars between northern and southern hemispheres, the tropics, and the higher latitudes.

The IWMI Global Map of Irrigated Area (GMIA) map and related products is published on a website that includes full documentation of the results and the techniques used:

http://www.iwmigiam.org

The map has a nominal resolution of 10 km² per pixel, as monthly time series NOAA AVHRR (1997-1999) images provide the core data. The SPOT Vegetation monthly 1-km data of 1999 was also used in identifying and delineating classes, with irrigation within the forest cover in Africa and South America identified using 100m resolution JERS-1 radar imagery.  The 30-150 meter hi-resolution Landsat derived imagery (GeoCover) was used to refine irrigated and land-use classes. Extensive use has been made of groundtruth data from a wide range of sources, including extensive IWMI work in the Ganges and Krishna basins in India, by AIT team in Thailand, the innovative Degree Confluence Project data that samples the World at every 1 degree by 1 degree based on volunteer contributions, and the IWMI’s ground truth data of the World (http://www.iwmidsp.org). Masks of rainfall, elevation, temperature, and forest cover have also been used to define and refine the classification.

The GIAM provides 28 unique irrigated area classes of the World, with 10 surface water classes and 18 groundwater\conjunctive use classes. The characteristic spectral and time-series signatures are attached for each of the 28 classes. These characteristics indicate whether the area is single, double or continuously cropped.  The estimated areas of irrigation per pixel were extracted using a new technique called sub-pixel de-composition technique, which is described in the documentation and “area story” of the website. It must be noted that there is a more disaggregated irrigated area map with 343 classes. Such a map maybe useful for users specifically interested in greater details, specifically when one is focused on a particular country or continent. But the users will have to further refine class names based on local knowledge.

The website additionally contains three other global agriculture products and their associated documentation:

·          Global map of Rainfed Cropped Areas (GMRCA)

·          Global map of all land use/land cover (LULC) areas (GMLULCA)

·          Global IWMI generic 951 class map (Generic-IWMI-951)

Work on irrigated area mapping continues @ IWMI with: 1) refinement and upgrading the global map using high resolution images and other refinements, and 2) the development of a much more detailed 500-m pixel scale map of the entire Indian sub-continent, consisting of 7 Countries.

The extent of estimated gross irrigated area has some significant ramifications for current understanding of irrigation and its contribution to global food security, especially in relation to total global cropped area, estimated at 1.539 billion ha in year 1999 (also at http://www.iwmigiam.org.

The team seeks feedback from all users, readers and interested parties, and continues to harvest groundtruth data to verify and upgrade the map. We welcome your views and contributions, please!!

References

FAO, 1998. FAOSTAT, Internet version (http://www.fao.org). Food and Agricultural Organization of the United Nations, Rome.

Food and Agriculture Organization. 2001. FAOSTAT database. Available http://apps.fao.org. Cited February 9, 2001.

Framji, K.K., Garg B.C., and Luthra, S.D.L. 1981. Irrigation and drainage in the world :a global review. Third Edition, ICID, New Delhi.

Ramankutty, N., and J. A. Foley. 2003. LBA Regional Historical Croplands, 5-min, 1900-1992 (Ramankutty and Foley). Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.

Ramankutty, N. and Foley, J.A. 1999. Estimating historical changes in global land cover: Croplands from 1700 to 1992. Global Biogeochemical Cycles 13, 997-1027.

Ramnakutty, N., and J. Foley, 1998. Characterizing patterns of global land use: An analysis of global croplands data. Global Biogeochemical Cycles, 12(4):667-685.

Postel, S., 1999. Pillar of Sand: Can the Irrigation Miracle Last? (New York: W.W. Norton). Pp. 313.

Siebert, S., Hoogeveen, J. & Frenken, K. (2006): Irrigation in Africa, Europe and LatinAmerica - Update of the Digital Global Map of Irrigation Areas to Version 4. FrankfurtHydrology Paper 05, Institute of Physical Geography, University of Frankfurt, Frankfurt am Main, Germany and Food and Agriculture Organization of the United Nations, Rome, Italy.

Siebert, S., Döll, P., Hoogeveen, J., Faurès, J-M., Frenken, K. & Feick, S. 2005. Development and validation of the global map of irrigation areas. Hydrology and Earth System Sciences, 9, 535-547.

Siebert, S., Döll, P., Hoogeveen, J., 2002. Global map of irrigated areas version 2.1. Center for Environmental Systems Research, University of Kassel, Germany, and FAO, Rome, Italy. Online documentation and download of 5 min map of irrigated area version

Thenkabail, P.S., Biradar, C.M., Turral, H., and Schull, M. 2005. A Global Map of Irrigated Area at the End of the last Millennium using Multi-sensor, Time-series Satellite Sensor Data. Draft Documentation for: http://www.iwmigmia.org. International Water Management Institute (IWMI), Colombo, Sri Lanka.

van Schilfgaarde, Jan, 1994. Irrigation- a Blessing or a Curse. Agricultural Water Management 25: 203-219.

Webb P., 2001. Land Degradation in Developing Countries: What is the Problem?. International Journal of Agricultural Resources, Governance and Ecology 1 (2): 124-36Wiebe

Webb, P. 2002.  Cultivated Capital: Agriculture, Food Systems and Sustainable Development, Food Policy and Applied Nutrition Program. Tufts Nutrition. DISCUSSION PAPER NO. 15. The Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy, USA.