A global approach to estimate irrigated areas – a comparison between different data and statistics

Abstract

Abstract. Agriculture is the largest global consumer of water. Irrigated areas constitute 40 % of the total area used for agricultural production (FAO, 2014a) Information on their spatial distribution is highly relevant for regional water management and food security. Spatial information on irrigation is highly important for policy and decision makers, who are facing the transition towards more efficient sustainable agriculture. However, the mapping of irrigated areas still represents a challenge for land use classifications, and existing global data sets differ strongly in their results. The following study tests an existing irrigation map based on statistics and extends the irrigated area using ancillary data. The approach processes and analyzes multi-temporal normalized difference vegetation index (NDVI) SPOT-VGT data and agricultural suitability data -both at a spatial resolution of 30 arcsec -incrementally in a multiple decision tree. It covers the period from 1999 to 2012. The results globally show a 18 % larger irrigated area than existing approaches based on statistical data. The largest differences compared to the official national statistics are found in Asia and particularly in China and India. The additional areas are mainly identified within already known irrigated regions where irrigation is more dense than previously estimated. The validation with global and regional products shows the large divergence of existing data sets with respect to size and distribution of irrigated areas caused by spatial resolution, the considered time period and the input data and assumption made.

Irrigated areas grow faster than the population

“…Meier et al. () observes that, globally, official institutions might underestimate irrigated areas by 22%, with some regions in Africa and Asia having irrigated areas that are >10 3 times larger than those reported by the Food and Agriculture Organization (FAO).…”

“…In the case of irrigation agriculture, the discrepancies are large: the irrigated areas attested by Thenkabail et al (2009b) for India are 40% larger than those reported by the Indian Ministry of Water. Meier et al (2018) observes that, globally, official institutions might underestimate irrigated areas by 22%, with some regions in Africa and Asia having irrigated areas that are >10 3 times larger than those reported by the Food and Agriculture Organization (FAO).…”

Statistical Data Collection Methodologies of Irrigated Areas and Their Limitations: A Review

“…Meier et al . () mapped the irrigated agriculture by integrating RS and GMIA and marked missing areas in India mainly situated within densely irrigated regions already present in the statistics. They found the absence of minor irrigation practices from statistics responsible for this (e.g.…”

“…In these regions, under-reporting of irrigated land belonging to small and marginal farmers is likely to occur as the majority of these farmers buy water and do not own pumps, and thus could be overlooked during minor irrigation enumeration (Srivastava and Kumar, 2007;Kumar et al, 2013). Meier et al (2018) mapped the irrigated agriculture by integrating RS and GMIA and marked missing areas in India mainly situated within densely irrigated regions already present in the statistics. They found the absence of minor irrigation practices from statistics responsible for this (e.g.…”

“…The third combines both country-based statistics and RS-based data sets to develop maps of irrigated agriculture (e.g. Pervez and Brown, 2010;Zhu et al, 2014;Salmon et al, 2015;Meier et al, 2018).…”