Global warming is expected to account for about 20 percent of the global increase in water scarcity this century. It is predicted that global warming will alter precipitation patterns around the world, melt mountain glaciers, and worsen the extremes of droughts and floods.
Global water consumption increased sixfold in the last century - more than twice the rate of population growth - and will continue growing rapidly in coming decades. Yet readily available freshwater is a finite resource, equivalent to less than one percent of the water on Earth.
What's more, water and populations are unevenly distributed across the globe; arid and semi-arid regions receive only two percent of all surface runoff yet account for 40 percent of the global land area and house half of the world's poor. Finally, our existing freshwater resources are under heavy threat from overexploitation, pollution, and global warming. Given these trends, equitably providing adequate water resources for agriculture, industry and human consumption poses one of the greatest challenges of the 21st century.
The physical evidence of water scarcity can be found in increasing magnitude around the world, affecting rich and poor countries alike. Nearly three billion people live in water scarce conditions (over 40 percent of the world's population), and this situation could worsen if current growth trends continue. The manifestations of pervasive water poverty include millions of deaths every year due to malnourishment and water-related disease, political conflict over scarce water resources, extinction of freshwater species, and degradation of aquatic ecosystems. Roughly half of all wetlands have already been lost and dams have seriously altered the flow of roughly 60 percent of the world's major river basins.
Fig. 1: Areas of Physical and Economic Water Scarcity
Source: UN-Water 2007
Water scarcity is not a factor of absolute quantity; it occurs frequently in both dry and moist climates. Rather, it is a relative concept comparing the availability of water to actual use. Desert regions, for example, do not classify as water scarce if demand for water is low. However, scarcity may exist in water-abundant areas if there is heavy population pressure, excessive pollution, or unsustainable consumption levels. Together, these forms of physical water scarcity affect every continent and approximately one-fifth of the world population.
In the United States and Europe, the average individual uses between 200 and 600 liters of water per day, compared to the 20 liters deemed to be the minimum daily requirement for drinking, washing, cooking and sanitation. Such unsustainable consumption levels have led to localized areas of water scarcity and significantly altered freshwater ecosystems. The massive Colorado River in the United States, which feeds the otherwise desert-like cities of Los Angeles, San Diego, and Las Vegas as well as millions of agricultural fields, now runs dry before reaching the ocean. As a consequence, the Colorado River Delta, which once supported plentiful plant and animal life, is now significantly diminished.
Fig. 2: Per Capita Water Use, 2000 (cubic meters per year)
Source: Earth Trends
On the other hand, economic water scarcity occurs when water resources are abundant relative to water use, but insufficient infrastructure or financial capacity prevents people from accessing the water they need. This dilemma plagues an additional 1.6 billion people worldwide, predominantly the rural poor and particularly in Africa. For this reason, additional investment in the water sectors of developing countries could play a transformative role in poverty alleviation.
Slum dwellers, for example, typically pay five to 10 times more per unit of water than do people with piped water, and in rural households, women and children may spend the majority of their day fetching water from distant, and often unsafe, sources. The majority of the world's poorest people are smallholder farmers, most of whom rely on low-yield, rain-fed agriculture, and their livelihoods are constantly threatened by inconsistent precipitation and drought.
F ig 3: Poor households in developing countries spend higher portions of their income on water than families in industrialized nations. Source: UN-Water 2007
Agriculture accounts for 70 percent of global water consumption and up to 95 percent of consumption in some developing countries. Irrigated agriculture, which accounts for only 20 percent of cultivated land but over 40 percent of the global harvest, has significant implications for the future of water availability and food security worldwide.
The world's population is projected to increase by 50 percent by 2050. With economic development and higher incomes around the world, per capita food consumption--and subsequently water consumption--will also rise. In particular, as more people in developing countries can afford diversified diets including meat and vegetables, agricultural water use will rise dramatically; it takes ten times more water to raise a kilogram of beef than a kilogram of wheat.
Fig. 4: Water Requirements for Food Production: Producing a kilogram of beef meat requires ten times more water than producing a kilogram of wheat.
Source: UN-Water 2007
Climate change is expected to account for about 20 percent of the global increase in water scarcity this century. The Intergovernmental Panel on Climate Change (IPCC) predicts that global warming will alter precipitation patterns around the world, melt mountain glaciers, and worsen the extremes of droughts and floods. If measures are not taken to mitigate climate change, a study by the UK Meteorological Office predicts that severe droughts now occurring once every 50 years could occur every other year by 2100.
Africa is one of the continents most vulnerable to increased drought frequency and intensity, but it is also the least equipped to adapt due to ongoing economic water scarcity. Increasingly frequent, severe drought in Central Africa as well as expanding agriculture have reduced the surface area of Lake Chad, once one of Africa's largest wetlands, by 90 percent. The population relying on the Lake Chad Basin for water includes 20 million people in Chad, Niger, Nigeria and Cameroon.
Figure 5: The Disappearance of Lake Chad
Source: UNEP 2002
With continued population growth, increased per capita consumption, and anticipated climate change, the global water situation appears bleak. Since water scarcity is a highly localized issue determined by regional climatic and demographic factors, a single solution will not solve all of the world's water scarcity problems. However, improved management, more water efficient technologies, and support for the world's most vulnerable countries and ecosystems will likely play leading roles. According to the UN-backed World Commission on Water, coping with water scarcity will require global investment of $100 billion per year. Willingness to invest this sum will be vital to the future of human well-being and economic development in all countries of the world.
From Crystal Davis: EarthTrends Update: November 2007 "The Multiple Dimensions of Water Scarcity"