Irrigation is the most important water use sector accounting for about 70% of the global freshwater withdrawals and 90% of consumptive water uses. While the extent of irrigation and related water uses are reported in statistical databases or estimated by model simulations, information on the source of irrigation water is scarce and very scattered. Here we present a new global inventory on the extent of areas irrigated with groundwater, surface water or non-conventional sources, and we determine the related consumptive water uses. The inventory provides data for 15 038 national and sub-national administrative units. Irrigated area was provided by census-based statistics from international and national organizations. A global model was then applied to simulate consumptive water uses for irrigation by water source. Globally, area equipped for irrigation is currently about 301 million ha of which 38% are equipped for irrigation with groundwater. Total consumptive groundwater use for irrigation is estimated as 545 km³ yr⁻¹, or 43% of the total consumptive irrigation water use of 1277 km³ yr⁻¹. The countries with the largest extent of areas equipped for irrigation with groundwater, in absolute terms, are India (39 million ha), China (19 million ha) and the USA (17 million ha). Groundwater use in irrigation is increasing both in absolute terms and in percentage of total irrigation, leading in places to concentrations of users exploiting groundwater storage at rates above groundwater recharge. Despite the uncertainties associated with statistical data available to track patterns and growth of groundwater use for irrigation, the inventory presented here is a major step towards a more informed assessment of agricultural water use and its consequences for the global water cycle

Abstract.A new version of a digital global map of irrigation areas was developed by combining irrigation statistics for 10 825 sub-national statistical units and geo-spatial information on the location and extent of irrigation schemes. The map shows the percentage of each 5 arc minute by 5 arc minute cell that was equipped for irrigation around the year 2000. It is thus an important data set for global studies related to water and land use. This paper describes the data set and the mapping methodology and gives, for the first time, an estimate of the map quality at the scale of countries, world regions and the globe. Two indicators of map quality were developed for this purpose, and the map was compared to irrigated areas as derived from two remote sensing based global land cover inventories.

Irrigation is the most important water use sector accounting for about 70% of the global freshwater withdrawals and 90% of consumptive water uses. While the extent of irrigation and related water uses are reported in statistical databases or estimated by model simulations, information on the source of irrigation water is scarce and very scattered. Here we present a new global inventory on the extent of areas irrigated with groundwater, surface water or non-conventional sources, and we determine the related consumptive water uses. The inventory provides data for 15 038 national and sub-national administrative units. Irrigated area was provided by census-based statistics from international and national organizations. A global model was then applied to simulate consumptive water uses for irrigation by water source. Globally, area equipped for irrigation is currently about 301 million ha of which 38% are equipped for irrigation with groundwater. Total consumptive groundwater use for irrigation is estimated as 545 km³ yr⁻¹, or 43% of the total consumptive irrigation water use of 1 277 km³ yr⁻¹. The countries with the largest extent of areas equipped for irrigation with groundwater, in absolute terms, are India (39 million ha), China (19 million ha) and the United States of America (17 million ha). Groundwater use in irrigation is increasing both in absolute terms and in percentage of total irrigation, leading in places to concentrations of users exploiting groundwater storage at rates above groundwater recharge. Despite the uncertainties associated with statistical data available to track patterns and growth of groundwater use for irrigation, the inventory presented here is a major step towards a more informed assessment of agricultural water use and its consequences for the global water cycle

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Irrigation projects have been the subject of much bad press coverage because of the sometimes very damaging environmental and social impacts associated with large-scale projects such as dams, declining aid to agriculture and falling rates of economic returns to irrigation since the heyday of the 1970s. Yet irrigation remains one of the most crucial inputs into farming and therefore a potentially important poverty reduction tool for the 21st century. We review some of the evidence surrounding trends in investments in irrigation and the reasons behind the decline. We also provide a framework for analysing the positive and negative impacts of irrigation on poverty, how these might differ by the type of irrigation technology and review some of the evidence of these impacts. We reach a number of conclusions about the conditions under which irrigation is most likely to have a positive impact on the poor, but we also report that the evidence is patchy, and usually not gathered in such a way as to allow easy conclusions to be drawn.

Abstract. GlobWat is a freely distributed, global soil water balance model that is used by the Food and Agriculture Organization (FAO) to assess water use in irrigated agriculture, the main factor behind scarcity of freshwater in an increasing number of regions. The model is based on spatially distributed high-resolution data sets that are consistent at global level and calibrated against values for internal renewable water resources, as published in AQUASTAT, the FAO's global information system on water and agriculture. Validation of the model is done against mean annual river basin outflows. The water balance is calculated in two steps: first a "vertical" water balance is calculated that includes evaporation from in situ rainfall ("green" water) and incremental evaporation from irrigated crops. In a second stage, a "horizontal" water balance is calculated to determine discharges from river (sub-)basins, taking into account incremental evaporation from irrigation, open water and wetlands ("blue" water). The paper describes the methodology, input and output data, calibration and validation of the model. The model results are finally compared with other global water balance models to assess levels of accuracy and validity.

Irrigated agriculture accounts for 70% of global water withdrawals and therefore contributes substantially to global water scarcity. This article focuses on the impact of the increasing demand for biofuel on global water resources in the coming decade. Based on biofuel production projections for 2008 and 2017, it was estimated that currently around 1% of all water withdrawn for irrigation is used for the production of bio-ethanol, mainly produced from irrigated sugar cane and maize. In 2017 the amount of water to be withdrawn for biofuel production would increase by 74% if agricultural practices remain the same. It is, however, likely that in 10 years the increase will be less, mainly due to crop diversification in favour of rainfed crop species. Even though globally the amount of water withdrawn for the production of biofuels is modest, locally water scarcity problems may worsen due to irrigation of bio-ethanol feedstocks. In this context there is reason for concern in countries with fast-developing economies like India, China, Thailand and South Africa where the growing demand for food and energy causes an increased competition for already scarce water resources. This situation will be aggravated if the projected bio-ethanol production will come from irrigated sugar cane.