Most of the crops in the region have died, because of a very dry season.
Note: If you have a well, the drought has not affected you as badly.
You lose all crops, or just some, if you have a well. If you have a crop insurance, it pays out, and crop yield is calculated in the normal way.
All crops are lost and yield no revenue this year. If the player owns a well, at least one crop is guaranteed to survive, and each remaining crop has a 50% chance of surviving. Owning multiple wells will not increase the odds. If the player owns a crop insurance, crop yield is calculated in the normal way, as the insurance pays out.
WikiPedia entry on Drought:
Sahel Farming Practices: