Niger, Mali, Mauritania and Burkina Faso have been badly affected by food shortages. Click on the map below for information on the situation in each country.
Niger is the worst affected country - children are starving to death every day in parts of the south, aid agencies say. The World Food Programme says that 2.5m people need food aid - almost a quarter of the population. Some 32,000 children need food aid and medical help soon or they will starve.
Niger was the world's second poorest country even before poor rains and locust invasions devastated last year's crops. This time of year is always known as the "lean season" - last year's harvests have run out and this year's crops are not yet ready.
Northern areas of Mali, which border the Sahara desert, are also suffering acute food shortages. A recent survey showed that 16% of people in the regions of Gao and Kidal were acutely malnourished, WFP says. The government says 1.5m people need food aid.
Mauritania was worst hit by last year's locust invasions which have worsened the effects of poor rains across the region. But it has a much smaller population and so fewer people - 600,000 - need help than in Niger and Mali, the WFP says.
Some 500,000 people lost their crops in Burkina Faso last year. Many people in the region are subsistence farmers and have little money to buy food if their harvests fail.