"For centuries, water has been a potent weapon between warring states. When Pisa was at war with Florence, Leonardo da Vinci and Machiavelli planned to divert the Arno and leave Pisa dry."
"For at least as long, water has been a casus belli. India and Pakistan have contested one another’s access to the Indus River system; a 2006 study commissioned by the Defense Department said, “for over a half century, bitter rivalry over river resources” has arguably “been one of the leading causes of full-scale warfare between them.” Meanwhile, while India and Bangladesh have had standoffs over the Ganges. In the last 50 years, Israel and Syria have fought over the rights to the Jordan River, and Brazil and Paraguay have argued over control of the Paraná.
Such conflicts and uses of water as a weapon are now controlled by hundreds of international agreements. But climate change could increase the possibility of new water wars as some flows become anemic and others become unusable torrents. But as a new study by Heather Cooley and Peter H. Gleick of the Oakland-based Pacific Institute pointed out, “Most trans-boundary water agreements” are “based on the assumption that future water supply and quality will not change.”