ELECTRONIC	h   t   t   p   c o l o n   s l a s h   s l a s h   p e r c dot o r g   s l a s h   a r t i c l e s   s l a s h   d e s e r t i f i c a t i o n   d a s h   s a h e l	http://perc.org/articles/desertification-sahel	1