Saturday was World Water Day 2014. This year’s theme centered on the water-energy nexus, a topic which has become increasingly important in recent years.
According to the United Nations, energy production currently accounts for 15% of global water use, a number which is projected to grow to 20% within the next two decades. In the US, this number is significantly higher; the US Geological Survey estimates that electricity production alone makes up 49% of all water use.
Unfortunately, people tend too often to overlook the water-energy nexus until a catastrophic event happens. Water plays a vital role in the entire lifecycle of energy production, and it remains extremely vulnerable to the deleterious consequences that may arise from each step in the process – from extraction to refining to generation to distribution and beyond.
We know, for instance, than at least 20% of streams in West Virginia are heavily degraded due to mountaintop removal mining, an incredibly destructive form of coal extraction. In addition, we have seen several recent mishaps at other stages the process, whether it was the massive Freedom Industries chemical spill on the Elk River (refining), Saturday’s oil tanker spill outside of Houston (distribution), or the major coal ash spill on the Dan River.
Thermal pollution and water quality
But there exists another, less understood impact of energy production on freshwater resources – thermal pollution. The US gets 91% of its electricity from thermoelectric power plants; this category largely includes nuclear power plants and plants that run on fossil fuels. Thermoelectric plants generate massive amounts of heat during electricity generation process. This heat builds up within the plant and forces plant operators to draw in huge amounts of freshwater to cool the generators.
Once-through cooling systems, which take in water once for cooling and then discharge it back into waterways, make up 31% of the US’s power plant fleet. These systems require 20,000-60,000 gallons of freshwater for cooling per megawatt hour (MWh) of energy produced. As a result, the Sierra Club estimates that power plants suck up more than 135 trillion gallons of water (PDF) each year for cooling alone.
This staggering total exacts a serious toll upon aquatic environments. Dicharged water temperatures are, on average, 8-12ºC warmer than the intake temperatures. As Madden, Lewis, and Davis noted in a 2013 study,
Aquatic organisms are highly dependent on specific thermal conditions in aquatic environments; water temperatures above or below optimal thermal regimes can cause stress or even death.
Such thermal pollution can negatively alter aquatic ecosystems in a number of ways. It can reduce the solubility of oxygen, stymie animal growth rates, change nutrient cycling processes, and increase the toxicity of chemicals like heavy metals and pesticides. Accordingly to Madden, Lewis, and Davis, increasing water temperatures by 7ºC has been shown to halve key biological processes, such as growth and reproduction. It’s no surprise, then, that power plants are responsible for the deaths of trillions of fish each year.
How water quality affects energy production
Interestingly enough, however, elevated water temperatures can also harm the efficiency of thermoelectric power plants. As water temperatures increase and stream levels drop, both the suitability and availability of cooling water decreases. During the severe heat wave that struck Western Europe in the summer of 2003, France saw its nuclear energy capacity fall by 7-15% for five consecutive weeks. This event marks a harbinger for our future in a warming world.
Climate change will reduce thermoelectric power production
According to a 2013 article in the journal Global Environmental Change (paywall), climate change will ensure that river temperatures increase significantly for a large swathe of the planet, while low river flows (lowest 10th percentile) will decrease for one-quarter of the global land surface area. Throughout much of the US, mean river temperatures are projected to increase by at least 2ºC, while high water temperatures will climb by 2.6-2.8ºC.
This spike in high water temperatures will be particularly critical for power plants, as they will occur during the period at which both water temperatures and energy demand are highest – the peak of summer. The Clean Water Act sets restrictions on the maximum temperature of water withdrawn and discharged by power plants; while the specific thresholds may vary by state, the temperature is commonly set between 27ºC and 32ºC. Research shows that more than half of all power plants with once-through cooling systems already exceed these numbers, demonstrating the vulnerability of the electricity system to global warming.
Using these numbers, van Vliet et al projected the impact that climate change will have on thermoelectric power plants (paywall) due to the combination of higher water temperatures and decreased river flows. They found that summer capacity for these plants will fall by 4.4-16% from 2031-2060. Moreover, these plants appear extremely sensitive to major reductions (greater than a 90% drop) in output as a result of global warming; the same study concludes that these events will increase nearly three-fold.
The Great Lakes region appears particularly vulnerable to falling electric output in a greenhouse world due to its heavy reliance on an aging fleet of coal-fired power plants. The National Climate Assessment notes that 95% of the Midwest’s electricity generating infrastructure (PDF) will likely see declines in output due to higher temperatures. As climate change increases stress simultaneously on aquatic ecosystems, drinking water supplies, and electricity production, potential conflicts over water uses will almost certainly increase among stakeholders.
Those of us who wish to protect our vital freshwater resources, like the Great Lakes, cannot afford to focus solely upon this sector, given its inextricable links to other areas. We need to worry as well about the stability of our climate and the makeup of our energy system. Renewable energy technologies use substantially less water than fossil fuel plants and will help shift us away from carbon-intensive energy sources. A 2012 study shows that if the US invests heavily in energy efficiency and renewable energy production, by 2050, water withdrawals and water consumption for energy production would fall by 97% and 85.2%, respectively. This shift would save 39.8 trillion gallons of water.
If we want to truly be stewards of our freshwater resources, we need to act as stewards for our climate.