Shrinking Freshwater Resources: Part II

Not only is freshwater resources from surface supplies are vulnerable to being overused and depleted, groundwater resources are equally vulnerable and are being increasingly used in many areas of the world and to the point of depletion. Groundwater depletion can be defined as the rate of natural recharge to the aquifer being less than the rate of abstraction and discharge (Wada et al., 2010). Wada et al. (2010) study explains that areas prone to high levels of groundwater abstraction include North-East Pakistan, North-West India, North-East China, the central valley of California, and central US to name a few. They found that total global groundwater depletion totalled to 39% of the total yearly groundwater abstraction, which is an alarming rate for our global resources to be depleted.

Causes for groundwater depletion is a result of the overexploitation of these resources for agricultural, domestic, and industrial purposes. For example, areas in the world which has little access or supply to surface freshwater resources use groundwater systems as an alternative. Climate change is expected to have a huge impact on rainfall patterns over Africa, causing some areas to experience more droughts and others more flooding. Africa highly depends on rainfall and surface water sources and with this core supply reducing, alternative sources like groundwater is expected to be further relied upon for agricultural, domestic and industrial use as an adaptive method to climate change (Taylor et al., 2009). However, MacDonald et al. (2012) has found that there is a limit to how much groundwater resources can be used to supply populations in Africa. The study found that for low intense use, a groundwater borehole must be able to provide >0.1 l s^-1 whereas urban populations or large commercial scale irrigation schemes will require at least 5 l s^-1. Hence it is important to recognise that while populations use groundwater resources as an alternative resource, it may not be sufficient to keep up with the increasing demand for freshwater resources e.g. from an increase in population in Africa, ultimately leading to the depletion of groundwater resources.
In countries like the United States, local groundwater supplies are depleted for hydraulic fracturing to recover fossil fuels. Hydraulic fracking requires large amounts of water, and in a period where demand for energy is high, alternative solutions like fracking are adopted to fulfil that energy need. And thus, groundwater resources are highly affected. Water used for hydraulic fracturing increased from 10 to 55 million gallons of water in Michigan (Burton Jr er al., 2014). Michigan is considered to have an abundant amount of groundwater resources, but the demand and need for energy will only push for hydraulic fracturing processes in other areas, and thus the groundwater resources in those areas are likely to be highly impacted too.
India is the world largest user of groundwater resources, but these resources are reaching unsustainable limits (World Bank, 2010). India is endowed with an abundance of groundwater resources but the depletion of this resource can be linked back to the green revolution. Surface water was highly used by many populations across India, however since it was not accessible, groundwater was used more extensively for agriculture and drinking purposes. 85% of drinking water in rural areas comes from groundwater supplies, and increasingly populated urban areas such as Delhi consumes almost 50% of groundwater (World Bank, 2010).

Impacts of groundwater depletion has wider implications and it includes not only the depletion of freshwater resources, but the quality of water will decrease as wells are being dug for more water, land subsidence will occur, streamflow depletion and the increased chances of sea water intrusion in coastal aquifers (Famigeltti, 2014). Hence the environment tends to suffer the consequences of this groundwater depletion. For example, a case study in the North China Plain exhibits these same consequences on the environment as well whereby cones of depressions have formed largely under the urban prefectures of Cangzhou and Hengshui, declining at a rate of 1.0 and 1.7 m/year (Changming et al., 2001). Also, land subsidence in the Xingang area of Tianjin affected the strength of the harbour structures and increased the vulnerability of this region to storms.
Coastal cities that relies on groundwater resources is at the risk of seawater intrusion and a great decline in the quality of drinking water. For example, a study by (Mtoni et al., 2012) has shown that in the city of Dar es Salam, Tanzania, shallow wells are dominated by sodium, calcium and chloride ions due to increasing seawater intrusion near boreholes located in the coast. Deeper aquifers are still more mineralised, but if the rate of groundwater overexploitation continues unsustainably, then these deeper aquifers are likely to deteriorate in quality as well.

Groundwater resources are just as important as surface water sources, and once over exploited to an unsustainable limit, it can be difficult to bring these resources back to its previous level and quality. The management of freshwater resources is highly important for human wellbeing, and agricultural, domestic and industrial use, although freshwater systems are generally isolated on regional scales and so regional scale management is required. Thus I would like to further explore how freshwater resources are currently being used and if it is managed properly, sustainable and without excess consumption of it.