Abstract
Water is a naturally circulating resource that is constantly recharged. Therefore, even though stocks of water in natural and artificial reservoirs help increase water resources available to human societies, the flow of water should be the main focus of water resources assessments. The climate system puts an upper limit on the circulation rate of available renewable freshwater resources (RFWR). Although current global withdrawals are well below the upper limit, more than two billion people live in highly water-stressed areas because of the uneven distribution of RFWR in time and space. Climate change is expected to accelerate water cycles, and thereby increase the available RFWR. This would slow down the increase of people living under water stress ; however, changes in seasonal patterns and increasing probability of extreme events might offset this effect. Reducing current vulnerability is the first step to prepare for such anticipated changes.
