Artificial Irrigation: Statistics.

From a Wikipedia page regarding Statistics about Irrigation, these are some interesting data:

- 94% of the application methods of irrigation water at field level is of the category surface irrigation, whereby the water is spread over the field by gravity.

- Of the remaining 6%, the majority is irrigated by methods requiring energy, expensive hydraulic pressure techniques and pipe systems like sprinkler irrigation and drip irrigation, for the major part in the USA.

 The source of irrigation water in these cases often is groundwater from aquifers. However, the exploitation of aquifers can also be combined with surface irrigation at field level.

- Irrigation schemes in the world use about 3 500 km3 water per year, of which 74% is evaporated by the crops. This is some 80% of all water used by mankind (4 400 km3 per year).

- The water used for irrigation is roughly 25% of the annually available water resources (14 000 km3) and 9% of all annual river discharges in the hydrological cycle.

- Of the total irrigated area worldwide 38% is equipped for irrigation with groundwater, especially in India (39 million ha), China (19 million ha) and the United States of America (17 million ha). Total consumptive groundwater use for irrigation is estimated as 545 km3/year. 

- Groundwater use in irrigation leads in places to exploitation of groundwater at rates above groundwater recharge and depletion of groundwater reservoirs.

References:

International Commission on Irrigation and Drainage (ICID). Link.

Bruce Sundquist, 2007. Chapter 1- Irrigation overview. In: The earth's carrying capacity, Some related reviews and analysis. Link.

S. Siebert, J. Burke, J. M. Faures, K. Frenken, J. Hoogeveen, P. Döll, and F. T. Portmann (2010). Groundwater use for irrigation – a global inventory. In: Hydrology and Earth System Sciences. Link.