Global Map of Irrigation Areas

China

The irrigated area was reported to be 53 820 300 ha in the 2000 cropping season [CN01]. The figures given by the report are limited to the provinces in China mainland and are based on census results.

The farm area for China Hong Kong SAR was reported to be 6 960 ha in the 2000 cropping season, while the area actually cropped was 2 710 ha [CN02]. Based on these statistics, the irrigated area in China Hong Kong SAR was estimated to be 2 000 ha.

There are large uncertainties regarding the irrigated area in China. Inventories based on remote sensing reported a much larger extent of areas under irrigation then the census based statistics. Therefore, the irrigated area has been estimated at 78 million ha for the 1992–93 cropping season [CN03]. The irrigated area per county was available for 1990 [CN04] and totalled about 46 million ha. The inventory is based on the agricultural census undertaken in the same year. In addition, irrigated areas were digitized from a 1:1 000 000 land-use atlas [CN05]. The atlas was published in 1990 and is based on satellite images and large-scale aerial photographs taken in the 1980s. Irrigated areas and paddy areas derived from the land-use map totalled about 68 million ha. The large discrepancy between the results of the agricultural census and the results of the land-use mapping also appears for total cropland, which was reported as 95 million ha (census) and 130 million ha (land-use atlas). This shows again the considerable uncertainty relating to land use in China.

In order to estimate irrigated area per county in the 2000 cropping season, three inventories were combined. Irrigated area per province was assumed to be as given in [CN01]. The downscaling to county values was achieved by combining the census results for the county level in 1990 [CN04] and the irrigated area per county as taken from the land-use atlas [CN05]. First, the upper and lower limits of irrigated area per province were computed by calculating the sum of minimum and maximum irrigated areas per county as taken from the two inventories:

It was assumed that the irrigated area per county was at least as high as the minimum of irrigated area taken from the two inventories plus the difference from the maximum value scaled by a coefficient s. The coefficient s was constant for all counties within the same province and was chosen so that the sum of the irrigated area in all counties equalled the irrigated area per province. It was possible to use this method for 23 of the 30 provinces in China mainland. In the provinces of Beijing and Tianjin, Guangdong, Jiangsu, and Zheijang, the computed lower limits of irrigated area were higher than the irrigated area reported for the provinces in 2000 (see the table above). This indicates either an overestimation of irrigated area in both inventories or a strong decline in irrigated areas between 1990 and 2000 in these provinces. Irrigated area per county was computed here by scaling the minimum of the irrigated area as reported by the two inventories. In contrast, the computed upper limit of irrigated area was lower than the irrigated area reported for 2000 in the provinces of Hebei, Heilongjiang and Jilin (see table above). This indicates either an underestimation of irrigated areas in both inventories or a considerable increase in irrigated areas in these provinces between 1990 and 2000. Irrigated area per county was computed here as a maximum of the two inventories plus the rainfed agricultural land scaled by a coefficient so that the sum of the computed irrigated areas per county equalled the irrigated area per province in 2000.

The irrigated areas were derived from the land-use atlas published in 1990 (scale: 1:1 000 000). The atlas was available in a printed hardcover version [CN05] and in a digital version [CN06]. The digital version had a lower resolution and consisted of fewer classes than the printed version. Therefore, fields classified as irrigated or as paddy were digitized from the printed atlas version for 754 counties, covering about 67 percent of the country area. The digital version of the map was used for the other counties, which are mainly located in southeast China and usually very small.

It was assumed that all the paddy-fields were irrigated. However, in 287 counties, covering about 9 percent of the country area, the sum of irrigated and paddy areas as derived from the land-use map was smaller than the total irrigated area of the related county. In these cases, the difference from the irrigated area was distributed to rainfed agriculture fields digitized from the land-use map. The total amount of irrigated area distributed to fields classified as rainfed was 1.5 million ha for the entire country.

The distribution of irrigated area by sub-national unit is listed in the table below.

References

[CN01]: National Bureau of Statistics. 2001. China statistical yearbook 2001 (available at http://chinadatacenter.org).
[CN02]: Agriculture, Fisheries and Conservation Department. 2002. Department annual report 2001/02 (available at http://www.afcd.gov.hk).
[CN03]: Frolking, S., Xianming, X., Yahui Z., Salas, W. & Li, C. 1999. Agricultural land-use in China: a comparison of area estimates from ground-based census and satellite-borne remote sensing. Glob. Ecol. Biogeog., 8: 407-416.
[CN04]: Skinner, G.W. 1997. China county-level data on population (census) and agriculture, keyed to 1:1M GIS map. Center for International Earth Science Information Network (CIESIN), (available at http://sedac.ciesin.columbia.edu).
[CN05]: Wu, C., ed. 1990. Land-use map of China (1:1 000 000 scale). Beijing, Science Press.
[CN06]: Chinese Academy of Sciences. 1994. Digital land-cover map of China. Beijing, Institute of Remote Sensing Applications.

Distribution of irrigated area in China by Province.