Review of global agricultural water use per country

Conclusions

Agriculture represents 70% of global water use. Yet, experience shows that the number of countries where agricultural water use is monitored with sufficient accuracy is limited. In most cases, gross irrigated areas are multiplied by an average unit water use to obtain an estimate of the country’s water use in irrigation. While the compilation of national statistics is necessary to benefit from local knowledge, their use in global assessment has proved too unreliable to allow for meaningful analysis.

The approach developed in this study relies both on the countries’ statistics and on modelling to provide a more reliable and more homogenous global dataset of country agricultural water use. By combining available information on the local of irrigated areas in countries, on irrigated cropping patterns and on the different elements of the climate, it is possible to develop a robust conceptual model to assessment amount of water diverted for irrigation. The development of "irrigation cropping calendars" for each country, based on FAO’s knowledge of the countries’ agriculture is probably one of the most sophisticated ways to ensure reliable assessment of water use in agriculture.

A sensitivity analysis would show that the weakness of the method lies in the use of the water requirement ratios, both for conceptual reasons and because of the scarce information available. Conceptually, when it is used at national level, water requirement ratio cannot accommodate return flows to the rivers or the aquifers. In large irrigation schemes or areas, it is therefore certain that the amount of water lost in conveyance or in drainage from irrigated fields is reused in irrigation downstream and that the "scheme" ratio can therefore be much higher than field ratio. The problem is particularly relevant in cascade irrigation of paddy rice in areas like South Eastern Asia. This study cannot distinguish between scheme and field water requirement ratios by lack of detailed information on the type of irrigation schemes. Water requirement ratio is therefore defined as the amount of water needed to satisfy agriculture in irrigated areas and the gross volume of water withdrawn from rivers and aquifers for irrigation purposes.

Future improvements in the assessment and monitoring of agricultural water use will have to come first from improvement of national monitoring capacities. At global level, it is likely that the methodology presented in this study will continue to be the most appropriate one to provide systematic, homogenous and relatively reliable country figures of agricultural water use. Further validations of the method will be possible when an increasing number of countries will present reliable data.

References

Your access to AQUASTAT and use of any of its information or data is subject to the terms and conditions laid down in the User Agreement.