It has been estimated that by the mid-1990s, 40% of the world’s population was suffering from serious water shortages. This is now increasing, with two-thirds of the population projected to be living in water-stressed countries by 2025, most of these in North Africa, the Middle East and West Asia. Prolonged droughts affect many countries in semi-arid areas such as the Sahel, southern Africa, northern China, India,
the western coast of South America, and Australia. Southern Europe and the Great Plains of the United States also suffer from water stress, over-abstraction of groundwater and desertification. Moreover, many arid regions are the focus of potential conflicts over water scarcity and there is a need to develop strategies to support peace and security. Challenges facing water managers in these areas include population growth, food security, salinity increases and pollution from various sources. Superimposed on these pressures, climate change is expected to increase water scarcity and the frequency of floods and droughts in many arid and semi-arid areas.