Today, only 16 percent of the world's croplands are irrigated, but those lands yield some 36 percent of the global harvest. In the developing countries, irrigation increases yields for most crops by 100 to 400 percent. Irrigation also allows farmers to reap the economic benefits of growing higher-value cash crops. Half or even two-thirds of future gains in crop production are expected to come from irrigated land. In the developing world, where about 20 percent of arable land is irrigated, the prevalence of irrigation varies widely within and among countries and crops.
Irrigation makes the greatest contribution to global food security in Asia.
Irrigated lands account for as much as 80 percent of food production in Pakistan, some 70 percent in China and over 50 percent in India and Indonesia. In Africa, where only about 10 percent of food production comes from irrigated lands, FAO calculates that irrigation has been developed on only 30 percent of 42.5 million hectares with irrigation potential. In many regions, water is being pumped out of the ground for irrigation faster than it can be replenished. Overpumping in India's Tamil Nadu state has lowered the water table by 25 to 30 m in a decade. Much of this water is wasted.