Agharta

Agharta is a manga series by Takahal Matsumoto. It was serialized in Ultra Jump.

Plot
After a major natural disaster, earth is slowly transforming into a desert in which mankind tries to survive. Water becomes a precious resource and the center of political intrigues. In the middle of this, a young boy, member of a gang, encounters a beautiful girl who's a merciless warrior and holder of the key to the save of humanity.