01308naa a2200157 a 450000100080000000500110000800800410001910000150006024500610007526000090013652009090014565000190105465000150107370000130108877300490110118703722014-11-17       2005    bl ---       0--  u    #d1 aHILLEL, D.  aThe sustainability of irrigation.h[electronic resource]  c2005  aIrrigation is the supply of water to agricultural crops by artificial means, designed to permit farming in arid regions and to offset periodic droughts in semiarid regions. Even in regions where total seasonal rainfall is adequate on average, it may be poorly distributed during the growing season and variable from season to season. Wherever traditional rain?fed farming is a high?risk enterprise, irrigation can help to ensure stable production. Irrigation has long played a key role in feeding expanding populations and is expected to play a still greater role in the future. Although irrigated land amounts to only some 17% of the world's cropland, it contributes well over 30% of the total agricultural production. That vital contribution is even greater in arid regions, where the supply of water by rainfall is least and the demand for water imposed by the bright sun and the dry wind is greatest.  aclimate change  airrigation1 aVLEK, P.  tAdvances in Agronomygv. 87, p. 55-84, 2005.