The development of water resources is a key element in the socio-economic development of many regions in the world. Water availability and rainfall are unequally distributed both in space and time. Shifting weather patternsare predicted to further affect the amount of rainfall in many regions. Some areas will become drier while others will see an increase in precipitation events. These changes will have untold consequences for the freshwater supply of the people living there. Decisions in water management planning must take this development into account.