The role of dams and reservoirs in the consumption of freshwater

IPCC AR5 report suggests that under climate change, surface freshwater resources will likely decline due to the increased variability in rainfall, river flow and snow melt and ice storage (Cisneros et al., 2014). Areas near the Mediterranean, Southern Africa and East Asia will likely experience lower rainfall and higher temperatures and thus some areas will become more water-stressed, and population growth and urbanisation will only add to this water stress. One adaptive method to climate change impacts is the construction of dams and reservoirs. Watts et al. (2011) strongly argues that dam construction can reduce the effects of climate change while increasing the resilience of water systems and contributing to ecosystem restoration. In this blog, I am going to explore the role of dams in addressing the needs of water stress areas, the benefits and the downfalls of dam construction.

Dams have multiple uses ranging from hydropower, inland navigation, flood control, water supply for domestic and industrial use, and water supply for irrigation. These uses can be highly beneficial for those most vulnerable to changes in e.g. rainfall. 94% and 66% of agriculture is rain-fed in sub-Saharan Africa and Asia, respectively, thus these populations are highly vulnerable to climate change (McCartney and Smakhtin, 2010). In Africa, climate change is predicted to increase droughts and rainfall will become more intense and concentrated within the space of a few months which results in floods and large runoffs (IPCC, 2007). Ideally dams can bridge the gap between rainfall variability and supply, as well as reducing the impacts of intense runoffs and floods (ICID). However, the construction of dams in these vulnerable areas may not be able to derive any benefits from it. For example, the Kariba Dam in Zambia was declared to be in “dire” condition as a result of droughts, which are intensified by climate change (Leslie, the NewYorker).

Throughout my blogs, I have been arguing how human consumption of freshwater have been unsustainable to the extent where water resources are declining across the globe, however a study by Pekel et al. (2016) presents an alternative viewpoint, suggesting that surface freshwater resources are in fact increasing. Pekel et al. (2016) explains that globally, surface water resources have permanently declined in areas such as the Middle East and Central Asia as a result of human activities and overconsumption, however there has been an increase in surface water elsewhere which is mainly through dams and reservoir filling. They found that 90,000km² of surface water has been permanently lost, however 184,000km² of permanent water has formed in areas that previously had no water and Asia gained the largest amount of permanent water of 71,000km² since 1984. In terms of quantifying freshwater resources, this study has shown that we have not lost a significant amount of freshwater, but instead we have gained almost double of what we lost. However, this does not identify whether the use of dams is sustainable; what are the impacts of dams on a hydrological regime and the local environment?

The Three Gorges Dam (TGD) is located in the Yangtze river basin and is one of the world’s largest dam with a 600km long reservoir and 4000km² storage capacity (Gleick, 2013). This dam has large benefits such as having a large storage capacity and thus an extensive water supply during periods of long drought, and reducing major flooding downstream of the Yangtze basin (Sun et al., 2012). However, there are significant concerns to the environment, and people’s health and livelihoods. For example, sediment retention can significantly damage downstream environments. Jingjiang River and Dongting Lake usually received sediments before the TDG was built, but now it supplies the Yangtze river with sediments due to the retention of sediments at the TDG (Sun et al., 2012). The decreased sediment loads can cause suffocation and abrasions to biota and habitats in the surrounding environment. Moreover, the alteration of the hydrological regime has huge implications on wetlands and lakes whereby the storage of water during the autumn period and release during winter and spring resulted in the decline of water levels in the Lake Dongting wetland. Water levels decreased by 2.11m with an extreme value of 3.02m in 2009 since the dam’s construction (Sun et al., 2012). Other environmental problems include eutrophication, algal blooms, the decline of certain fish species, and the erosion of downstream riverbeds (Xu et al., 2013). The water quality in 38 small tributaries had declined since 2003 from 14-29% by 2008 depending on the portion of the river and the frequency of algal bloom events increased from 3 to 26 between 2003 to 2010 (Xu et al., 2013). By 2008, approximately 1.13 million people were displaced and resettled to areas near the reservoir or in urban cities, however the resettlement of these populations did not consider the environmental carrying capacity of these populations thus having wider implications on local resources (Xu et al., 2013).

Concluding Thoughts:

The overconsumption and pollution of freshwater resources, and climate change largely influences water availability in many areas of the world, and so the use of dams can prove to be a solution to addressing water security issues. Storing water can provide for a constant supply of water and especially during periods of drought, thereby reducing water scarcity. The study by Pekel et al. (2016) explains that surface water supplies has increased as a result of dams and reservoirs, however, case studies such as the TDG shows that dams and reservoirs have wider implications to the local environment, water quality and populations living near water resources, such as the water level decline of Lake Dongting in the Yangtze river basin, or the decline in water quality. Thus, this should only raise concerns regarding the sustainability of using dams in addressing water scarcity issues and if we should use dams as a permanent solution for guaranteeing a constant supply of freshwater.