According to a recent study published in Nature, almost 90,000 km2 of surface water, roughly equivalent to that of Lake Superior, have disappeared altogether and an additional total of 72,000 km2 have transitioned from a permanent state to a seasonal state over the past three decades. During the same period, a cumulative area of 184,000 km2 of permanent water have formed elsewhere.
The study analyzed the Landsat satellite images and global data sets documenting surface water location and seasonality between 1984 and 2015. It was found that over 70% of global net permanent water loss occurred in the Middle East and Central Asia (mainly in five countries: Kazakhstan, Uzbekistan, Iran, Afghanistan and Iraq). These losses were caused by such factors as drought, dams that change the flow rate and direction of rivers, and unregulated withdrawal. Losses in Australia and the USA linked to long-term droughts were also evident.
The study reported that all continental regions showed a net increase in permanent water, except Oceania, which has a fractional (1%, 229 km2) net loss. Around 24 countries spread across all continents have each gained at least 1,000 km2 of new permanent bodies of water. Much of the increase come from reservoir construction and filling. Between 1984 and 2015, North America’s permanent water area increased by 17,000 km2. Asia has gained 71,000 km2 of permanent water, which is a 23% increase for the continent.
The location and persistence of surface water is both affected by climate and human activity. Human behavior and biological diversity may be changing in response to water distribution. According to the study, almost 52% of the planet’s truly permanent surface water exists in North America and the continent also holds 18% of the contemporary seasonal water. In contrast, Asia, with 60% of the human population, accounts for only 9% of the truly permanent and 35% of the contemporary seasonal water. Africa and Latin America have almost the same share of the world’s permanent water at around 9%. Europe, including Russia, has 22% of the permanent water and 18% of the contemporary seasonal water.
Surface water is only a part of the water resource. Ground water is another important source of fresh water. A number of studies have documented that groundwater resources are decreasing at alarming rates and face increasing pressure due to climate variability, population pressure, and increases in energy demands. A study conducted by two scholars from the University of Twente in Netherlands reported that groundwater depletion occurs in many countries, including India, Pakistan, the United States, Iran, China, Mexico, and Saudi Arabia. Furthermore, emerging groundwater contamination and pollution risks are seriously reducing available groundwater resources.
Access to water is indispensable for sustainable development and can threaten the security of people, institutions and economies. The findings reported in these studies reinforce the need for water-resource management strategies that integrate climate and socio-economic dimensions. Otherwise, many areas will increasingly suffer from water shortages during droughts, resulting in reduced harvests and loss of income for farmers, threatening the livelihoods of whole communities, as warned by relevant scholars.