www.worldwatch.org). It is estimated that by 2025, 1.8 billion people will live in countries or regions with absolute water scarcity, with almost half of the world living in conditions of water stress.
Water scarcity has several definitions. Physical scarcity occurs when there is not enough water to meet demand; its symptoms include severe environmental degradation, declining groundwater, and unequal water distribution. Economic water scarcity occurs when there is a lack of investment and proper management to meet the demand of people who do not have the financial means to use existing water sources; the symptoms in this case normally include poor infrastructure.Large parts of Africa suffer from economic water scarcity.
A region is said to face water scarcity when supplies fall below 1,000 cubic meters per person, and absolute water scarcity is when supplies drop below 500 cubic meters a year.
World population is predicted to grow from 7 billion to 9.1 billion by 2050, putting a strain on water resources to meet increased food, energy, and industrial demands. But there are many other pressures, including increased urbanization and over consumption, lack of proper management, and the looming threat of climate change. According to the United Nations Food and Agriculture Organization and UN Water, global water use has been growing at more than twice the rate of population increase in the last century.
Agricultural water withdrawal accounts for 44 percent of total water withdrawal among members of the Organisation for Economic Co-operation and Development (OECD), but this rises to more than 60 percent within the eight OECD countries that rely heavily on irrigated agriculture. In the four transitional economies of Brazil, Russia, India, and China, agriculture accounts for 74 percent of water withdrawals, but this ranges from 20 percent in Russia to 87 percent in India.
Policymakers must introduce a variety of measures to address global water scarcity. One important initiative is to support small-scale farmers. Much of the public investment in agricultural water management has focused on large-scale irrigation systems. Farmers can also use water more efficiently by taking a number of steps, including growing a diverse array of crops suited to local conditions and adopting irrigation systems like "drip" lines that deliver water directly to plants' roots.
Climate change will affect global water resources at varying levels. Reductions in river runoff and aquifer recharge are expected in the Mediterranean basin and in the semiarid areas of the Americas, Australia, and southern Africa, affecting water availability in regions that are already water-stressed. In Asia, the large areas of irrigated land that rely on snowmelt and high mountain glaciers for water will be affected by changes in runoff patterns, while highly populated deltas are at risk from a combination of reduced inflows, increased salinity, and rising sea levels. And rising temperatures will translate into increased crop water demand everywhere.
About 66 percent of Africa is arid or semiarid, and more than 300 million people in sub-Saharan Africa currently live on less than 1,000 cubic meters of water resources per person.
To combat the effects of climate change, efforts must be made to follow an integrated water resource management approach on a global scale. This involves water management that recognizes the holistic nature of the water cycle and the importance of managing trade-offs within it, that emphasizes the importance of effective institutions, and that is inherently adaptive.
According to UN Water, each person in North America and Europe consumes at least 3 cubic meters per day of virtual water in imported food, compared with 1.4 cubic meters per day in Asia and 1.1 cubic meters per day in Africa.