Along the southern border of the Sahara, in the luckless region known as the Sahel, a drought has been going on for 20 years now. In the 1970s hundreds of thousands of people succumbed to the effects of crop failures and cattle die-offs, and today the millions of farmers and nomads who inhabit the Sahel are still living on the edge. One potent symbol of their plight can be seen from space: Lake Chad, once as big as Lake Erie, is now a third the size. But in that desolate image Solomon Isiorho sees a reason for hope. Some of that vanished water, he says, may still be available for use.