Energy Use by Water Supply in a Changing Climate

Dr. Weiwei Mo
Published: July 18,2016

Modern water and energy supplies are inextricably intertwined. Providing one resource requires a substantial amount of the other. This interrelationship is commonly referred to as the “water-energy nexus.” In the U.S., treating and pumping water alone represents an average of 4% of the total electricity consumption with vast variance among regions (e.g. >20% of total electricity use in California). Additionally, energy flows associated with providing chemicals and services to water systems ranges from 25 to 200% of the direct energy demands. These energy consumptions are heavily dependent on fossil fuels - about 82% of the total energy use - producing large amounts of greenhouse gases (GHGs) and other air pollutants.

In the past decade, water shortage and water scarcity has led to a change in urban water supply, particularly in densely populated coastal regions. Alternative water sources such as desalinated seawater, reclaimed water and even harvested rainwater have been introduced to augment existing water supplies. While utilizing alternative water sources can be a potentially viable strategy, shifts in local water supply profiles are usually associated with significant energy, economic and environmental costs, leading to new or elevated stresses in energy supply, public funds and ecosystem services. Given that energy and water are managed separately, energy stresses are very likely to result in the construction and operation of new power infrastructure, which may further exacerbate water shortages considering the water-energy nexus. Eventually, these additional costs will be partially or fully reflected in water and energy prices, causing ripple effects on social equity and economic development.

 

Average electricity demand of selected water supply and average freshwater demand of selected energy supply in the U.S.

 

In addition to population growth, the water-energy nexus is further compounded by the changing climate. In 2013, North America, Asia and Europe experienced one of the most intense and prolonged summer heat waves and droughts in 60 years, which resulted in severe water and energy shortages, as well as tremendous economic losses. In the U.S., the hydrologic cycle is accelerating with increasing flooding and downpours in the northeast. Sea level rise and subsequent seawater intrusion have threatened freshwater availability in many coastal regions. Collectively, these climate change effects dramatically increase the vulnerability of future water supply.

Traditional water supplies mainly rely on groundwater and surface water, both of which are highly sensitive to climate changes. Surface water supply, which accounts for 94% of total water withdrawal, is usually obtained from rivers, lakes or constructed reservoirs. These natural or engineered bodies of surface water are usually regulated in order to protect their ecological functions. When water level falls due to drought or increased withdrawal, it is imperative to develop alternative or more distant water sources. Similarly, degraded groundwater levels escalate water supply costs and may eventually force us to seek more energy and cost intensive alternatives. Snowpack contains a substantial amount of freshwater and provides essential functions as the spring melt feeds most rivers and lakes in the U.S. The expected warming climate across the country would reduce snowpack storages, leading to shifts in streamflow patterns as melting occurs earlier in spring.

Water sustainability index based on projected water withdrawal and water availability for year 2050. Dark red, red, yellow, and white represent extreme, high, moderate, and low risks to sustainable water supply, respectively. Figure 2(a) presents water sustainability index with climate change effects. Figure 2(b) presents water sustainability index without climate change effects (obtained from NRDC).

Climate change influences water quality in a number of ways, including increased flooding or storm events, elevated water temperature, stimulated algal blooms and sea level rise. Increased storm events and flooding can cause increases in suspended solids, as well as nutrient and pollutant fluxes and incidences of combined sewer overflow. Bodies of water react to climate change almost immediately by increasing water temperature. Collectively, these physical and chemical changes in the water can lead to enhanced growth of algae and cyanobacteria, lowering water quality and increasing energy use and costs during treatment. Seawater intrusion resulting from sea level rise has already occurred in coastal communities within New Jersey, South Carolina, Georgia and Florida, resulting in increased salinity of local groundwater along with its associated difficulties during treatment.

Given the sensitivity of water quantity and quality to the future climate, linking the water-energy nexus with climate change is especially important. With the right planning and decision making, government agencies, along with water and energy utility companies, will be better positioned to help mitigate water and energy issues in the future.

Dr. Weiwei Mo is an assistant professor in the Department of Civil and Environmental Engineering at University of New Hampshire working on sustainable water and energy management.