The next three weeks will be crucial in bringing relief to roughly 18 million people facing hunger across eight countries in West Africa, the U.N. humanitarian chief said Thursday. Valerie Amos, the United Nations humanitarian affairs and emergency relief coordinator, said the U.N. and its partners have raised half of the almost $1 billion needed to fund humanitarian relief operations in West Africa's Sahel region but donors need to make an extra effort. A combination of drought, failed crops, insect plagues, high food prices, and conflict has led to an unfolding hunger crisis in the Sahel region. "The critical period is in the next few weeks before the rainy season starts and things become even more difficult to get aid to the people," Amos told Reuters AlertNet in Diourbel, about 134 kilometers west of Senegal's capital Dakar, where she was visiting malnutrition treatment centers.