Wherever you are in the world, chances are you are sitting on water. Drill down deep enough and you’ll find it. Beneath the Earth’s surface aquifers are natural reservoirs that contain groundwater. Collectively they constitute the largest amount of liquid freshwater on Earth. They are a vital source of drinking water for humans and livestock, and also offer a potential solution to increasing global problems of water scarcity.
Why is groundwater so important? First, it’s generally a more reliable source of water than surface water, which is naturally protected from contamination. Second, groundwater acts as a natural buffer from drought, helping to smooth out rainfall patterns, thereby increasing resilience to climate change. Finally, it can generally be found close to the point of demand.
It’s for these reasons and more that groundwater is the main source of water in low-income countries. Only 2% of the rural population in Southern Asia, 5% of the rural population in Southeastern Asia and 20% of rural dwellers in sub-Saharan Africa rely on surface water sources.
Groundwater in agriculture
Groundwater is used by farmers the world over. In developed countries with drier climates, such as Spain and the Southwestern USA, groundwater underpins thriving high-value farming. Elsewhere the situation varies. Asia and Africa, for instance, are strikingly different. In Asia, groundwater is highly exploited, particularly in India and China. In India alone, a million new tube wells are sunk each year. In Africa, it is a greatly underexploited resource. To get at it you need wells, pumps, a supply of energy and know-how – things that many African farmers still lack.
Globally, about 1,000 cubic kilometers (km³) of groundwater is withdrawn each year: enough to cover the entire island of Cyprus with a meter of water. Half or more of this is taken by smallholder farmers. In India, 600 million people directly benefit from groundwater-supported agriculture. Many researchers have demonstrated that this approach is often more productive and equitable than centrally run irrigation schemes.
However, if too much groundwater is used, the consequences can be disastrous.
The increase in groundwater extraction is startling: in 1969, India withdrew 25 km3 of water. By 2010, fuelled by cheap new pumps and subsidized electricity, that figure had risen tenfold. It’s demand driven: if you have your own pump, all you have to do is sink a well to get as much water as you want, whenever you want. In the words of one researcher: Groundwater irrigation has evolved into a ‘colossal anarchy’.
If extraction exceeds recharge, as it does in some parts of India and China, the water table begins to drop and more and more energy is needed to pump water from wells. There is also an increased risk of salinity in some areas.
A sustainable resource
With good science and sensible policies, groundwater can be effectively and sustainably managed. If we can work out how much and how quickly aquifers are recharged, we can also work out the sustainable yield and design long-term strategies to maintain water levels for future generations that cater for the multiple uses that groundwater must serve, including the environment such as by contributing to dry-season river flows.
Groundwater is an ‘invisible commons’ – farmers cannot directly see the resource, so find it difficult to judge how much they can sustainably use. In addition, pricing incentives designed to boost agricultural production, such as cheap power for pumps, have actually worsened problems of depletion in some areas. Establishing sustainable use, therefore, will be dependent on the creation of effective and equitable institutions to govern and regulate the resource. This will be challenging as most groundwater sources come under the jurisdiction of multiple authorities. Also, farmers using groundwater have been fiercely resistant to curbs on their access.
In Africa, there is a fantastic opportunity to develop groundwater as a new and sustainable resource. Shallow wells can be supplemented with simple pump bores. Lessons learned in Asia can help African policymakers to avoid past mistakes, and implement robust and equitable management practices.