Not only does irrigated agriculture account for most global
freshwater withdrawals, it is also typically the residual claimant on
water within a given river basin. Therefore, in order to deduce the
supply of water for irrigation at any point in time, it is important to
understand not only the hydrological flows, but also the
residential, industrial and environmental demands for water. If
the latter expand, and total water availability in the river basin is
unchanged, then the effective supply of water for irrigation