An Irrigated Area Map of the World (1999) Derived from Remote Sensing

Abstract

"It is necessary to accurately quantify the area and intensity of irrigation in the world in order to properly understand its contribution to food production and security, and to estimate its water use, as competition for water increases with rising urban and industrial needs and the recognition of environmental water requirements. Satellite remote sensing offers a relatively cheap, repeatable and accurate technology to estimate and monitor irrigated areas. This research report presents the results of a global analysis of multi-temporal time series at nominal 10 kilometer pixel resolution. Statistics of irrigation at country level are derived from these maps for different seasons and for the entire year (annualized) for the nominal year of 1999. Three methods of area abstraction are used and compared, and three methods of accuracy assessment are applied. The annualized irrigated areas of the world at the end of the last millennium were about 480 Mha of which there were 263 Mha for season 1, 176 Mha for season 2, and 41 Mha for continuous cropping. Of this, Asia alone accounts for 78 percent (375 Mha) with 59 percent from China and India. The country statistics are compared with FAO country-level statistics (see Annex I). The IWMI GIAM 10 km V2.0 map were tested based on 3 sources of independent data resulting in accuracies between 84 and 91 percent with errors of omission not exceeding 16 percent and errors of commission less than 21 percent. The total area available for irrigation (TAAI; the nearest equivalent to FAO's equipped area)was 412 Mha. The global irrigated area mapping (GIAM) products (e.g., maps, statistics, web maps) are made available through a dedicated web portal (http://www.iwmigiam.org). The detailed methodology is also made available through the web portal. The focus of this research report is on the results of the GIAM mapping effort."