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WATER POLITICS

Via Future Directions International, a report on the world’s groundwater supplies:

Key Points

• New estimates suggest there are 22.6 million km³ of groundwater within the top two kilometres of the earth’s surface.
• No more than six per cent of the global groundwater supply has been renewed within the last 50 years.
• A better understanding of groundwater use and renewal is necessary to implement effective and sustainable water management policies.
• Increased groundwater governance is the most effective means to sustainably manage groundwater resources.

 

Summary

Groundwater is a vital resource for many regions of the world, particularly during times when surface water becomes scarce. In some regions, the abstraction of groundwater far exceeds renewal and threatens long-term water security. It is possible that groundwater supplies in these areas will eventually be exhausted. Without the security of groundwater many regions will not be able to sustain agricultural, industrial, municipal and household water use during dry-periods. Ineffective management of groundwater supplies could lead to disruptions in food and water security as surface water sources come under increased pressure from climate change. To secure groundwater supplies for the future, a better understanding of groundwater use and renewal will be necessary. Increased governance will also better ensure groundwater is used sustainably and aquifers are not exhausted.  

 

Analysis

A new study has estimated how much groundwater exists below the earth’s surface. Existing estimates have relied upon models developed in the 1970s that do not measure the rate of groundwater renewal. The study estimates that globally there is approximately 22.6 million km³ of groundwater, enough to evenly cover the entire surface of the world to a depth of 180 metres. Only a relatively small amount of this water is suitable for use. Water that is safe to use would only cover the surface of the earth to a depth of three metres if evenly distributed.

The study suggests that groundwater is replenished at a slower rate than originally thought. The vast majority of global groundwater, known as ancient groundwater, has been stored for thousands or millions of years. For the most part, this water is too far below ground or contains too high a level of trace elements to be suitable for human consumption. Only about six per cent of groundwater stored in the first two kilometres of the earth’s surface is less than 50 years old, suggesting that it takes a considerable amount of time to replenish easily exploitable groundwater aquifers. This so-called “modern” groundwater is being tapped for human use and is the most vulnerable to climate change and other environmental pressures, such as contamination from agriculture or industry. In many regions of the world the amount of time it takes to renew the groundwater supply appears to be slower than the rate at which it is being used.

The global audit of aquifers provides a much needed update to models developed in the 1970s and reiterates the important role groundwater plays in the hydrological cycle. Further studies that focus on specific aquifers will be necessary, however, to gain a better understanding of groundwater use in specific contexts. Graham Fogg, an American hydrogeologist, has suggested that some aquifers are replenished at much faster rates than others. He argues that aquifers are interconnected in complex ways and it is possible for one aquifer to naturally replenish another, even if they are located considerable distances from each other. While the global study provides a broad overview of the world’s groundwater situation, more localised investigations are required to understand rates of renewal in specific aquifers.

Global Groundwater Use

Groundwater is unevenly distributed throughout the world. The study indicates that it is concentrated in jungle and mountainous areas, such as the Amazon, Andes and Congo, which receive consistently high levels of moisture. Relatively little groundwater is present in arid regions, such as the Sahara and Gobi Deserts. It is mainly in drier regions, where water is scarce, that demand for groundwater is greatest. Generally, it is densely populated, arid parts of the world that are facing the greatest levels of water stress.

Aquifers are often a water source of last resort. As they are more resilient to drought than surface water sources, they are tapped into once surface water sources become scarce. Unless properly managed, groundwater is not a long-term solution to severe water shortages and increased demand, as it is a finite resource. In the past 50 years, as global demand for water has risen, groundwater extraction has increased by more than 300 per cent. In many parts of the world such an increase is unsustainable and many aquifers are at risk of depletion as extraction rates outstrip renewal. A July 2015 study found that water reserves in 21 of the 37 largest aquifer systems in the world have declined since 2003. If groundwater is to continue to serve as a buffer against the vagaries of surface water supplies they need to be sustainably managed.

Agriculture is a major consumer of groundwater. Approximately 60 per cent of groundwater extracted globally is used for agricultural purposes and about 40 per cent of irrigation used for food production is sourced from groundwater reservoirs. India, China and the United States have the largest areas equipped for groundwater irrigation and therefore have the largest stake in ensuring that such water is properly managed. Ensuring that groundwater is sustainably utilised will be vital for future food security. A further 25 to 40 per cent of the global drinking supply is derived from groundwater sources. These uses make groundwater the world’s most extracted raw material, according to the US-based National Ground Water Association. Groundwater also aids in replenishing streams, lakes, wetlands and other water-based ecosystems. If this natural water source is significantly altered, there could be significant environmental impacts that affect surface water supplies.

East Asia, South Asia and the Middle East most at Risk

Groundwater provides Asia with about 30 per cent of its freshwater. If this resource is depleted it is likely to threaten the region’s food security and economic development. China is particularly reliant upon groundwater supplies as surface water has come under increased pressure due to widespread development and contamination. It has been reported that thousands of rivers have simply ceased to exist due to the overexploitation of both surface and groundwater sources. With surface water supplies dwindling, many have turned to the extraction of groundwater to fill the gap. Several aquifers in China are already overexploited and failure to secure surface water sources could lead to a greater reliance on groundwater supplies.

In South Asia, groundwater systems are coming under increased pressure. Before every monsoon season, the Indian Government measures water levels in 13,000 observation wells. In the 2015 study it was found that water levels in the majority of these wells were lower than the previous year. In almost all Indian states, the 2015 water level was lower than the ten year average, indicating overuse.

In the Middle East, groundwater supplies are also facing depletion. Saudi Arabia, Syria, Iraq and Yemen have over-pumped their groundwater supplies to the point that many wells are going dry. Between 2002 and 2009 the Middle East lost 144 million km³ of water, more than enough to fill the Dead Sea, mainly due to the over-abstraction of groundwater. If such use continues the region will increasingly be forced to import greater amounts of food as domestic production will decrease. The importation of food and developing other sources of water will have economic repercussions for the region.

Conclusion: Effective Management of Groundwater Requires Increased Governance

Groundwater is an important resource that sustains economic and environmental systems, especially during times of drought when surface water sources come under increased pressure. Some regions of the world are likely to experience more droughts as a consequence of climate change, the impact this could have on groundwater is largely unknown. Without adequate levels of management and oversight, however, it is highly likely that groundwater supplies will decrease, perhaps to the point of exhaustion. Globally, there is a need for more effective groundwater regulation. Now that the amount of groundwater has been more accurately measured and recharge rates are slower than first thought, such regulation is more necessary than ever.