| 英文摘要: | Climate change may constrain future electricity generation capacity by increasing the incidence of extreme heat and drought events. We estimate reductions to generating capacity in the Western United States based on long-term changes in streamflow, air temperature, water temperature, humidity and air density. We simulate these key parameters over the next half-century by joining downscaled climate forcings with a hydrologic modelling system. For vulnerable power stations (46% of existing capacity), climate change may reduce average summertime generating capacity by 1.1–3.0%, with reductions of up to 7.2–8.8% under a ten-year drought. At present, power providers do not account for climate impacts in their development plans, meaning that they could be overestimating their ability to meet future electricity needs. Electric power generation can be disrupted by adverse climatic conditions. Although vulnerabilities are specific to each generation technology, capacity reductions are most likely to occur during extreme heat and drought events1, 2, 3, 4. During drought conditions, when streamflow is low and temperatures are high, ‘base-load’ coal and nuclear power plants may lack the necessary cooling water to generate at full capacity1, 5. Insufficient streamflow can also limit electricity production at hydroelectric dams2. Peaking technologies—such as gas turbines4, solar cells6 and wind turbines7—are vulnerable to acute changes in atmospheric parameters such as air temperature. Drought- and heat-related capacity reductions are especially problematic, because they are likely to occur during periods of high electricity demand3, 4. From 2001 to 2008, a series of droughts caused electricity shortages in the American Southeast8, the Pacific Northwest9, and continental Europe10. As concentrations of atmospheric carbon increase, drought events are anticipated to increase in frequency, duration and intensity11. Failure to account for climate-attributable capacity reductions during peak demand periods may cause unforeseen electricity shortages. At present, the effects of climate change on electric power systems are poorly understood, leaving balancing authorities with little choice but to assess infrastructure reliability based on historical climate conditions. Previous research has focused on climate impacts to large nuclear- and coal-fired power plants located along major rivers in the Eastern US and Europe1, 12. Although vulnerable, these facilities represent only about 10% of US generation capacity1. By contrast, the Western US (a region of the world that is expected to experience significant climatic and hydrologic changes) relies heavily on alternative generation technologies, with renewables and combustion turbines comprising roughly 56% of generating capacity13. These alternative technologies are expected to represent a greater portion of the future electricity grid14. So far, there has been no comprehensive effort to assess the impacts of climate change on a region’s overall generation portfolio. Thus, it has not been possible to gauge the effects of climate change on electricity reliability at the grid level. Nor has it been possible to assess how investments in certain generation technologies and transmission infrastructure may increase the resilience of regional power systems. We assess future electricity reliability in the Western US by evaluating capacity reductions to 978 vulnerable electric power stations under three carbon emissions scenarios. Our study focuses on the power service region of the Western Electricity Coordinating Council (WECC), which at present supplies about 200 GW of summertime generating capacity13. WECC encompasses 14 states in the Western US, and is electrically autonomous during normal operating conditions15, 16, allowing conclusions to be drawn about network reliability. To quantify climate-attributable reductions in generating capacity, we isolate vulnerable facilities based on generation technology and cooling water source, identify climatic and hydrologic factors that impair power generation, produce daily simulations of hydro-climatic parameters using a physically based modelling system, and relate these parameters to achievable capacity at each facility using a mass and energy balance-based approach. The Western power grid employs a diverse array of generation technologies, each of which is vulnerable to different climatic and hydrologic factors. We investigate five generation technologies: steam turbine, combustion turbine, hydroelectric, wind turbine and photovoltaic. For steam turbine facilities (that is, ‘base-load’ coal and nuclear power plants), generating capacity is constrained by available streamflow, with cooling water demands being dictated by the enthalpy of air and water entering the cooling system5. Combustion turbines and photovoltaic cells experience capacity reductions with increasing air temperatures4, 6. For hydroelectric facilities, generating capacity is constrained by available streamflow2. Wind turbine performance depends on wind speed and air density7. In all, six parameters are required to assess impacts on power generation: streamflow, stream temperature, air temperature, vapour pressure, wind speed and air density. For turbine-based technologies, we apply energy and mass balances to the generator and cooling system to relate achievable capacity to hydro-climatic parameters. For photovoltaic cells, an empirical approach is used. Equations relating generation capacity to hydro-climatic factors can be found in Supplementary Section 2.1. Impacts to existing facilities are considered to be representative of future impacts, given that base-load coal, nuclear and gas facilities are expected to retain 85% of their capacity by 2040, and no cumulative retirements are expected for combustion turbine or renewable generation sources14. We evaluate impacts to generating capacity at peak load conditions, because this is when power systems are likely to experience the greatest strain (see Supplementary Section 5.1). Under these conditions, both ‘base-load’ and ‘peaking’ generation sources are likely to be deployed, meaning that impacts to either generation mode will affect overall electricity reliability. Hydro-climatic parameters are modelled at a daily time step for both the historical period (1949–2010) and the future period (2010–2060) at a spatial resolution of 1/8-degree, using the variable infiltration capacity (VIC) hydrologic model17, 18, and a semi-Lagrangian stream temperature model19 (see Supplementary Section 2.2). We force the modelling system with gridded observed meteorological data for the historical period20, and downscaled forcings from two global climate models (GCMs) for the future period21. To capture a range of possible futures, we use the A2, A1B and B1 emissions scenarios proposed by the Intergovernmental Panel on Climate Change. These scenarios place bounds on anthropogenic warming, based on divergent trends in carbon emissions. Variations between GCM models represent the primary source of uncertainty for this study, and are therefore incorporated into the results. Secondary sources of uncertainty—including environmental flow requirements and unreported plant specifications—are explored and quantified in Supplementary Section 3. By mid-century (2040–2060), climate change may reduce average summertime generating capacity by 1.0–2.7 GW, with potentially disruptive impacts occurring in California and the desert Southwest. Vulnerable facilities account for 46% of existing capacity in the WECC region and, among individual facilities, impacts range from a 4% increase in capacity to a 14% decrease in capacity. Figure 1 shows potential impacts to individual facilities and Fig. 2 shows annualized power generation curves for representative Southwestern and Northwestern regions. Generating capacity decreases for all hydrologic regions considered except the Pacific Northwest (a region expected to receive more precipitation21), with the greatest impacts occurring in the desert Southwest (a region expected to experience higher temperatures and less rainfall21). For the California and Colorado river basins, climate change may reduce summertime capacity by 2.0–5.2% in an average year. These reductions are mainly attributable to thermoelectric facilities, for which generating capacity is linked to air temperature and available streamflow. For the Pacific Northwest, where hydroelectric power makes up a majority of generating capacity, no relationship between climate change and generation capacity is observed. These findings suggest that transmission infrastructure may play a greater role in ensuring electricity reliability, as traditional thermoelectric capacity is more frequently disrupted by extreme heat and drought (see Supplementary Note). Strengthening transmission capacity between Northern and Southern regions may help Southern states manage demand during a drought event, without significantly compromising power reliability in the North.
|
