Climate Trends and Challenges of the Energy-Water Nexus
Most power generation facilities rely on a significant quantity of water, primarily for cooling. The most recent USGS water use survey (2005) reports that thermoelectric power accounts for approximately 41% of total freshwater withdrawals in the United States—more than any other water-use sector. Although most water use for this sector is not highly consumptive (less than 5% of national freshwater consumption budget), projections indicate possible increasing thermoelectric power consumption caused by a shift from “high-volume, low-consumption” once-through cooling plants toward closed-cycle cooling plants that withdraw less water but consume almost twice as much per unit of power produced.
Many electric power generators report high-priority water resource problems related to reduced water availability and/or increased water temperatures. These situations of physical water risk have led plants to temporarily shut down, reduce power generation, or make structural modifications to access cooling water. Situations of physical water risk can lead to increased reputational risk (perception of being a water hog”), regulatory risk (violation of thermal discharge permits), or financial risk (investor concerns and higher-cost replacement power).
LimnoTech conducted a study for the Electric Power Research Institute (EPRI 2010) to investigate the importance of reliable water supplies to the electric power industry and to identify relevant trends in water quantity and quality. This study found that water resource trends are complex: they can be influenced by a range of controllable and noncontrollable factors, and often reflect the integrated effects of natural and anthropogenic drivers such as climate variability, landscape change, water use, and regulations. The LimnoTech study noted that trends in precipitation and temperature can influence hydrology and water temperature over decadal and multi-decadal scales. In the U.S., the greatest influences appear to be occurring in the Southeast, Northwest, and Southwest, and include decreasing precipitation, increasing air temperature, decreasing snowpack, earlier snowmelt, and increasing drought. It is not just climate variation, however, that influences water resource trends and makes the past a poor predictor of the future. Society’s alteration of the landscape, and the capture, movement, consumption and regulation of water can influence water availability and quality.
Landscape changes such as increased impervious surfaces, wetland drainage, damming of rivers, and water diversions can alter the volume, timing, magnitude, and quality of surface water, and can also affect groundwater. These factors may relate to trends of decreasing base flows and/or increasing stream temperatures. Some drivers of water resource trends are not easily controlled, such as variable climate, landscape changes that occurred long ago (e.g., wetland draining, river impoundment, land development), and increasing regional populations. Other drivers such as water use, regulation, and future landscape changes are controllable, and may present an opportunity to positively influence water resources. It is not a steady-state world, and electric utilities are increasingly in a position where it is imperative to understand and adapt their water resources management. Power plants must adapt to a wider range of climate and water resources variability under which they can operate without excessive water risk.
In regions where benefits can be justified, electric utilities should, and often must, consider solutions that promote water conservation and use efficiency (in-plant reuse, reclaimed water sources, water banking, dry or hybrid cooling systems). It is important for all water stakeholders to be proactively involved in science and technology research and integrated water planning. Continued exploration of synergies among the water, industry, agriculture, and energy sectors will build bridges among water users, and allow for development of collaborative and innovative solutions. We as a society have the power to positively influence water sustainability by promoting green infrastructure, improving water use efficiency, controlling withdrawals and consumption through regulation, and collaboratively planning to reduce competition.