Michelle T.H. van Vliet

Water constraints on European power supply under climate change: impacts on electricity prices

Recent warm, dry summers showed the vulnerability of the European power sector to low water availability and high river temperatures. Climate change is likely to impact electricity supply, in terms of both water availability for hydropower generation and cooling water usage for thermoelectric power production. Here, we show the impacts of climate change and changes in water availability and water temperature on European electricity production and prices. Using simulations of daily river flows and water temperatures under future climate (2031‐2060) in power production models, we show declines in both thermoelectric and hydropower generating potential for most parts of Europe, except for the most northern countries. Based on changes in power production potentials, we assess the cost-optimal use of power plants for each European country by taking electricity import and export constraints into account. Higher wholesale prices are projected on a mean annual basis for most European countries (except for Sweden and Norway), with strongest increases for Slovenia (12‐15%), Bulgaria (21‐23%) and Romania (31‐32% for 2031‐2060), where limitations in water availability mainly affect power plants with low production costs. Considering the long design life of power plant infrastructures, short-term adaptation strategies are highly recommended to prevent undesired distributional and allocative effects.

Energy sector water use implications of a 2 °C climate policy

Quantifying water implications of energy transitions is important for assessing long-term freshwater sustainability since large volumes of water are currently used throughout the energy sector. In this paper, we assess direct global energy sector water use and thermal water pollution across a broad range of energy system transformation pathways to assess water impacts of a 2 °C climate policy. A global integrated assessment model is equipped with the capabilities to account for the water impacts of technologies located throughout the energy supply chain. The model framework is applied across a broad range of 2 °C scenarios to highlight long-term water impact uncertainties over the 21st century. We find that water implications vary significantly across scenarios, and that adaptation in power plant cooling technology can considerably reduce global freshwater withdrawals and thermal pollution. Global freshwater consumption increases across all of the investigated 2 °C scenarios as a result of rapidly expanding electricity demand in developing regions and the prevalence of freshwater-cooled thermal power generation. Reducing energy demand emerges as a robust strategy for water conservation, and enables increased technological flexibility on the supply side to fulfill ambitious climate objectives. The results underscore the importance of an integrated approach when developing water, energy, and climate policy, especially in regions where rapid growth in both energy and water demands is anticipated.

Global streamflow and thermal habitats of freshwater fishes under climate change

Climate change will affect future flow and thermal regimes of rivers. This will directly affect freshwater habitats and ecosystem health. In particular fish species, which are strongly adapted to a certain level of flow variability will be sensitive to future changes in flow regime. In addition, all freshwater fish species are exotherms, and increasing water temperatures will therefore directly affect fishes’ biochemical reaction rates and physiology. To assess climate change impacts on large-scale freshwater fish habitats we used a physically-based hydrological and water temperature modelling framework forced with an ensemble of climate model output. Future projections on global river flow and water temperature were used in combination with current spatial distributions of several fish species and their maximum thermal tolerances to explore impacts on fish habitats in different regions around the world. Results indicate that climate change will affect seasonal flow amplitudes, magnitude and timing of high and low flow events for large fractions of the global land surface area. Also, significant increases in both the frequency and magnitude of exceeding maximum temperature tolerances for selected fish species are found. Although the adaptive capacity of fish species to changing hydrologic regimes and rising water temperatures could be variable, our global results show that fish habitats are likely to change in the near future, and this is expected to affect species distributions.

Continental Runoff into the Oceans (1950–2008)

AbstractA common term in the continental and oceanic components of the global water cycle is freshwater discharge to the oceans. Many estimates of the annual average global discharge have been made over the past 100 yr with a surprisingly wide range. As more observations have become available and continental-scale land surface model simulations of runoff have improved, these past estimates are cast in a somewhat different light. In this paper, a combination of observations from 839 river gauging stations near the outlets of large river basins is used in combination with simulated runoff fields from two implementations of the Variable Infiltration Capacity land surface model to estimate continental runoff into the world’s oceans from 1950 to 2008. The gauges used account for ~58% of continental areas draining to the ocean worldwide, excluding Greenland and Antarctica. This study estimates that flows to the world’s oceans globally are 44 200 (±2660) km3 yr−1 (9% from Africa, 37% from Eurasia, 30% from South...

A physically-based model of global freshwater surface temperature

[1] Temperature determines a range of physical properties of water and exerts a strong control on surface water biogeochemistry. Thus, in freshwater ecosystems the thermal regime directly affects the geographical distribution of aquatic species through their growth and metabolism and indirectly through their tolerance to parasites and diseases. Models used to predict surface water temperature range between physically based deterministic models and statistical approaches. Here we present the initial results of a physically based deterministic model of global freshwater surface temperature. The model adds a surface water energy balance to river discharge modeled by the global hydrological model PCR-GLOBWB. In addition to advection of energy from direct precipitation, runoff, and lateral exchange along the drainage network, energy is exchanged between the water body and the atmosphere by shortwave and longwave radiation and sensible and latent heat fluxes. Also included are ice formation and its effect on heat storage and river hydraulics. We use the coupled surface water and energy balance model to simulate global freshwater surface temperature at daily time steps with a spatial resolution of 0.5 � on a regular grid for the period 1976–2000. We opt to parameterize the model with globally available data and apply it without calibration in order to preserve its physical basis with the outlook of evaluating the effects of atmospheric warming on freshwater surface temperature. We validate our simulation results with daily temperature data from rivers and lakes (U.S. Geological Survey (USGS), limited to the USA) and compare mean monthly temperatures with those recorded in the Global Environment Monitoring System (GEMS) data set. Results show that the model is able to capture the mean monthly surface temperature for the majority of the GEMS stations, while the interannual variability as derived from the USGS and NOAA data was captured reasonably well. Results are poorest for the Arctic rivers because the timing of ice breakup is predicted too late in the year due to the lack of including a mechanical breakup mechanism. Moreover, surface water temperatures for tropical rivers were overestimated, most likely due to an overestimation of rainfall temperature and incoming shortwave radiation. The spatiotemporal variation of water temperature reveals large temperature differences between water and atmosphere for the higher latitudes, while considerable lateral transport of heat can be observed for rivers crossing hydroclimatic zones, such as the Nile, the Mississippi, and the large rivers flowing to the Arctic. Overall, our model results show promise for future projection of global surface freshwater temperature under global change.

The future of the Rhine: stranded ships and no more salmon?

Climate studies show high likelihood of changing hydrological regimes in European rivers. Concerned authorities increasingly question the sustainability of current river management strategies. The aim of this paper is to apply the adaptation turning point (ATP) approach and demonstrates its potential for analysing turning points in river management strategies as a method to support authorities in decisions on adaptation to climate change. Two management strategies in the Rhine River basin were selected as case studies: (1) reintroduction of a sustainable population of Atlantic salmon and (2) inland shipping in relation to water depth variability. By applying the turning point approach, we search for answers to the following questions: when will these management strategies fail due to climate change impacts on the river’s hydrology? What adaptation measures exist to delay or avoid failure? The identification of adaption turning points is not easy, due to large scenario and model uncertainties in transient future projections of low-flow discharges and water temperatures. But the case studies demonstrate that the ATP approach is salient from a decision-maker’s perspective, because it addresses the timing of possible failure of current management strategies. Analysis of results allows policy makers to assess risks and the urgency for action and provides them with a time horizon for adaptation planning. It is also a valuable first step in the application of methods of formal appraisal of adaptation options when flexibility in planning is required.

Climate Impacts in Europe Under +1.5°C Global Warming

The Paris Agreement of the United Nations Framework Convention on Climate Change aims not only at avoiding +2°C warming (and even limit the temperature increase further to +1.5°C), but also sets long-term goals to guide mitigation. Therefore, the best available science is required to inform policymakers on the importance of and the adaptation needs in a +1.5°C warmer world. Seven research institutes from Europe and Turkey integrated their competencies to provide a cross-sectoral assessment of the potential impacts at a pan-European scale. The initial findings of this initiative are presented and key messages communicated. The approach is to select periods based on global warming thresholds rather than the more typical approach of selecting time periods (e.g., end of century). The results indicate that the world is likely to pass the +1.5°C threshold in the coming decades. Cross-sectoral dimensions are taken into account to show the impacts of global warming that occur in parallel in more than one sector. Also, impacts differ across sectors and regions. Alongside the negative impacts for certain sectors and regions, some positive impacts are projected. Summer tourism in parts of Western Europe may be favored by climate change; electricity demand decreases outweigh increases over most of Europe and catchment yields in hydropower regions will increase. However, such positive findings should be interpreted carefully as we do not take into account exogenous factors that can and will influence Europe such as migration patterns, food production, and economic and political instability.

Comments on “Effects of Environmental Temperature Change on the Efficiency of Coal- and Natural Gas-Fired Power Plants”

Efficiency of Coaland Natural Gas-Fired Power Plants” I their August 1, 2016 paper, Henry and Pratson use available historical power plant data and air and water temperatures to argue that the efficiency of power plants in the United States changes little with variations in air and water temperatures. Furthermore, they conclude that thermoelectric power plants are more resilient to climate change than previously concluded in Van Vliet et al. Here, we argue that this conclusion is only valid under the assumption that environmental regulations are ignored and that future cooling water availability will not change. Henry and Pratson estimate useable power plant capacity under conditions of climate change based on estimates of water temperatures for the year 2080 from van Vliet et al, concluding that “the summer average useable capacity of a 40-plant region (similar sample size to that of van Vliet et al. with n = 39 will be reduced by 0.4%”. They then conflate their work with van Vliet et al. and a similar study by Bartos and Chester and suggest, without further analysis, that the drought component on plant usable capacity is much greater than the temperature component. van Vliet et al. estimate useable capacity of power plants by simulating streamflows with a large-scale hydrologic model, stream temperatures with a one-dimensional, time-dependent numerical model and thermoelectric power plant characteristics derived from power plant databases. Furthermore, van Vliet et al. estimate useable capacity given limitations on available streamflow and assume that environmental jurisdictions in Europe and the United States will enforce environmental regulations for stream temperature. van Vliet et al. did not separate the impacts of drought and water temperature impacts, but it seems likely that the latter is at least as important as the impacts of drought. Nevertheless, Henry and Pratson appear to compare the percentage change in plant efficiency as a result of historical air and water temperature variations with the percentage change in useable capacity under climate change due to restrictions on available water supply and violations of state water temperature standards in van Vliet et al. Specifically, in section 4.3, Henry and Pratson state that their estimate of the impact of climate change on electricity production is significantly lower than those of van Vliet et al. and Bartos and Chester for the open-loop power plants they examined. Henry and Pratson further found reductions in η with increased Tw (for open-loop plants) up to 1 order of magnitude less than previous estimates. Finally they conclude that their results did not “support the conclusions of previous studies that increases in dry-bulb or wet-bulb air temperature will reduce the efficiency of all openand closed-loop plants”. Based on the Henry and Pratson paper Dominic Lenton, states that “A new study based on real-world data casts doubt on predictions from model-based studies that rising global temperatures will significantly reduce output from many power stations.” The analysis and conclusions in Henry and Pratson are based on their eq 2, which estimates power plant efficiency by regression analyses of plant efficiency on plant operating characteristics, and air and water temperature. This approach is entirely different than that of eqs 3a and 3b in van Vliet et al. (Supporting Information), used to estimate the impact of climate change and changing water resources and temperatures on plant useable capacity rather than plant efficiency. Based on historical analyses presented in Figure 4 and citing Madden et al., Henry and Pratson conclude that regulation on discharges of thermal effluent as regulated by section 316(a) of the Clean Water are not enforced. Henry and Pratson, therefore, state that “studies that have assumed open-loop plants reduce output at 27−30 °C will have overestimated the impact of water temperature on efficiency”. In their follow up analyses, Henry and Pratson assume that these regulation will also be ignored in the future. In addition, in their climate change impacts assessment, described in section 4.3, Henry and Pratson seem to ignore future changes in water availability, more or less assuming that in the future unlimited water or at least the same amount of water is available, although summer water availability is expected to decrease for many river systems in the US. Despite their finding on the low impacts of climate change on the electricity production the authors recommend the switch from once-through to closed-loop cooling system because they provide “the added benefit of reducing the temperature impact of climate warming on the efficiency and thus useable generating capacity of existing power plants”. In short, the “one order of magnitude” difference between Henry and Pratson and van Vliet et al. appears to be mostly (if not entirely) due to Henry and Pratson’s use of data-based efficiency estimators in combination with the assumption the environmental regulations will not be enforced and ignoring water scarcity. Under these assumptions it is not surprising that the “usable capacity” (efficiencies) they estimate, are not very sensitive to changes in air and water temperature and global warming. The results that Henry and Pratson report are not appropriate for comparing the impacts of climate change on power plant efficiency with the sensitivity of useable power plant capacity to climate change given existing environmental regulations in Europe and the U.S. and potential limits on the availability of cooling water, the primary objective of van Vliet et al. Therefore, we disagree with the conclusion of Henry and Pratson that power plants are (more) resilient to climate change. John R. Yearsley*,† Michelle T. H. van Vliet‡ Dennis P. Lettenmaier Fulco Ludwig‡ Stefan Vo ̈gele †UW-Hydro|Computational Hydrology Dept. of Civil and Environmental Engineering University of Washington Seattle, Washington 98195, United States

The Mekong's future flows under multiple drivers: How climate change, hydropower developments and irrigation expansions drive hydrological changes

The river flow regime and water resources are highly important for economic growths, flood security, and ecosystem dynamics in the Mekong basin - an important transboundary river basin in South East Asia. The river flow, although remains relatively unregulated, is expected to be increasingly perturbed by climate change and rapidly accelerating socioeconomic developments. Current understanding about hydrological changes under the combined impacts of these drivers, however, remains limited. This study presents projected hydrological changes caused by multiple drivers, namely climate change, large-scale hydropower developments, and irrigated land expansions by 2050s. We found that the future flow regime is highly susceptible to all considered drivers, shown by substantial changes in both annual and seasonal flow distribution. While hydropower developments exhibit limited impacts on annual total flows, climate change and irrigation expansions cause changes of +15% and -3% in annual flows, respectively. However, hydropower developments show the largest seasonal impacts characterized by higher dry season flows (up to +70%) and lower wet season flows (-15%). These strong seasonal impacts tend to outplay those of the other drivers, resulting in the overall hydrological change pattern of strong increases of the dry season flow (up to +160%); flow reduction in the first half of the wet season (up to -25%); and slight flow increase in the second half of the wet season (up to 40%). Furthermore, the cumulative impacts of all drivers cause substantial flow reductions during the early wet season (up to -25% in July), posing challenges for crop production and saltwater intrusion in the downstream Mekong Delta. Substantial flow changes and their consequences require careful considerations of future development activities, as well as timely adaptation to future changes.

Drought impacts on river salinity in the southern US : Implications for water scarcity

Hydrological droughts have a diverse range of effects on water resources. Whilst the impacts of drought on water quantity are well studied, the impacts on water quality have received far less attention. Similarly, quantifications of water scarcity have typically lacked water quality dimensions, whilst sectoral water uses are associated with both water quantity and quality requirements. Here we aim to combine these two elements, focussing on impacts of droughts on river salinity levels and including a salinity dimension in quantifications of water scarcity during drought and extreme drought conditions. The impact of historical droughts on river salinity (electrical conductivity (EC) was studied at 66 monitoring stations located across the Southern USA for 2000-2017. Salinity was found to increase strongly (median increase of 21%) and statistically significantly (p ≤ 0.05) during drought conditions for 59/66 stations compared to non-drought conditions. In a next step, a salinity dimension was added to water scarcity quantifications for 15 river basins in Texas. Water scarcity was quantified using data of sector water uses, water availability, river salinity levels and salinity thresholds for sector water uses. Results showed that the dominant factor driving water scarcity highly differed per basin. Increases in water scarcity were further compounded by drought-induced decreases in water availability, increases in sectoral water demands and increases in river water salinity. This study demonstrates that droughts are associated with important increases in river salinity, in addition to reduced water availability, and that both of these aspects should be considered when quantifying water scarcity. Alleviating water scarcity should therefore not only focus on increasing water availability and reducing water demands (quantity aspects), but also on improving water quality.