Water scarcity is defined as less than 1,000 m3 per capita of available, renewable freshwater per year (United Nations World Water Assessment Programme [WWAP] 2012, p. 124). The differentiation between areas of economic water scarcity (where storage, treatment and conveyance infrastructure are lacking) and absolute or physical water scarcity is illustrated in Figure 9.9 (WWAP 2012).
Sustainable freshwater supplies from surface and groundwater sources are critical for human and ecosystem needs, and for achieving the SDGs. Excessive withdrawals are often the cause of water scarcity. Lack of infrastructure, combined with rapid population growth, can lead to economic water scarcity, although there is not always agreement about the cause of water scarcity being physical, economic or indeed political in nature. Water of appropriate volume and quality is not always available at the right time or in the right place for a specific use.
Water scarcity is common throughout West Asia and the Asia and the Pacific region, and in arid parts of Africa, Latin America, the western United States of America and the Middle East. Factors that typically stress water resources include large populations, agricultural expansion and intensification, rainfall variability, rapid development, increasing urbanization, industrialization and climate change. The desiccation of the Aral Sea in Central Asia remains one of the most dramatic water-related environmental disasters of the 20th century. Most global climate model projections predict a 20 per cent rainfall decrease over the next 50 years in West Asia, with increased temperatures, evaporation and relative humidity all influencing water availability (UNEP 2016c, p. 12).
Desertification is a pressing problem in Africa’s sub-Saharan region, arising from climate change and internal migration (UNEP 2016d). Although physical and economic water scarcity prevails across Africa, its surface- and groundwater resources are considered underdeveloped, in terms of meeting human livelihood and development needs (UNEP 2016d). In this context, many small- to medium-scale water infrastructure projects are well suited to local water demand.
In parts of the developed world (e.g. Europe, North America, Australia), water scarcity is a challenge that is commonly addressed through large water infrastructure projects, such as dams, long-distance pipelines and desalinization plants. Given expected population growth trends, regions such as the Middle East, Africa and Asia need to address water scarcity in innovative and scale-appropriate ways, including water governance, rainwater harvesting and wastewater recycling, leapfrogging the conventional solutions of the past.
