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Figure 9.8: Retreat of Quelccaya ice cap in Peru between 1988 (left) to 2010 (right)


Source: Schoolmeester et al. (2018). 9


Tropical glaciers in the Andes account for more than 80 per cent of available freshwater for downstream populations and ecosystems in Latin American semi-arid tropic regions (UNEP 2013, p. 1). These are melting at an accelerating rate attributed to climate change (Chevallier et al. 2011; Rabatel et al. 2013), raising concerns about sustainable water supplies (Figure 9.8). Glacial retreat in the European Alps has accelerated over the last two decades (Huss 2012, p. 1132), while Central Asian glaciers have lost 27 per cent of their mass and 18 per cent of their area (Farinotti et al. 2015, p. 720; Yao et al. 2012).


9.4.4 Water scarcity Water scarcity is defined as less than 1,000 m3


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.


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


global climate model projections predict a 20 per cent rainfall


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.


9.5 Water quality


Although natural processes also generate water pollutants, human activities related to population growth, urbanization, agricultural expansion, transportation, and human and industrial waste discharges are typically the main sources of water pollution (UNEP 2016e). They include pathogens, nutrients, heavy metals and organic chemicals (Annex 9-1) from point sources (domestic, industrial or sewage pipeline discharges; septic tank leakage) and/or catchment non-point sources (land surface run-off from extensive diffuse agricultural use and urban areas following rainfall and snowmelt events).


century. Most


Water quality in many Latin American, African, Asian and Pacific rivers has generally decreased since the 1990s, although the majority are still in relatively good condition (UNEP 2016e). Water quality in many European rivers has improved since adoption of the EU Water Framework Directive


244 State of the Global Environment


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