We cut down trees in natural landscape, and when flooding, there is no trees or roots to slow it. Used to be the 6th largest freshwater lake. There was drought in africa before, and growing population. In order to survive, chad and many other countries draw too much water to irrigate, and lake chad shrank: example #2: aral sea. Cultivated cotton trade in that region and cotton is a very water required crop. 90% of water that"s supposed to reach aral sea shrinks never gets there as the rivers to aral sea have been diverted to irrigate instead. 276 transboundary river basins in the world: danube is shared by 18 countries. Water has to be shared in two ways: between its different uses (energy, cities, food, fisheries) Between users (tension over water will increase as scarcity increases: ganges: india, bangladesh and nepal, colorado: us and mexico, nile: egypt, jordon, west bank . Case study: water conflict in the middle east.