Water Resources System Performance Research Articles

Neglecting hydrological errors can severely impact predictions of water resource system performance

Risk-based decision making for water resource systems often relies on streamflow predictions from hydrological models. These predictions are integral for estimating the frequency of high consequence extreme events, such as floods and droughts. However, streamflow predictions are known to have errors due to various factors such as incomplete hydrological understanding, parameter misspecification, and uncertain data. Despite these errors being well known, they are frequently neglected when undertaking risk-based decision-making. This paper demonstrates that neglecting hydrological errors can impact on drought risk estimation for high stakes decisions with potentially severe consequences for water resource system performance. A generic framework is introduced to evaluate the impact of hydrological errors for a wide range of water resource system properties. This framework is applied in two Australian case study catchments, where we use a stochastic rainfall model, the GR4J hydrological model, a residual error model, and a simplified reservoir storage model to estimate water resource performance metrics (risk and yield). The results underscore the impact of neglecting hydrological errors on decision-making. In one case study catchment, the yield was over-estimated by ∼15%–55%, resulting in the (actual) risk of running out of water being ∼2–30 times larger than reservoir design. The magnitude of these errors in water resource performance metrics is striking, especially considering that the streamflow predictions appear reasonable based on typical performance metrics (e.g., NSE of ∼0.7). The errors in performance metrics stem from the complex propagation of hydrological errors through the water resource system modelling chain. By accounting for critically important hydrological errors we can mitigate highly erroneous risk estimates and improve decision-making related to water resource management.

Future potable water supply demand projection under climate change and socioeconomic scenarios: A case of Gshba subbasin, Northern Ethiopia

This paper aims to quantify the subbasin’s potable water supply demand forecast from 2023 to 2050 under various scenarios of climate change and socioeconomic development. The variability of the climate and the resulting problems with urbanization threaten the availability of water resources, especially in less developed countries like Ethiopia. Thus, the main objective of this study is showing the necessary to determine the amount of water needed in advance, in order to comply with the availability of water resources within a specified future period under different scenarios. Our indicator-based approach used a multicriteria decision-making technique. Accordingly, several important variables were considered, including climatological, anthropological, demographic, socioeconomic, and economic variables, in addition to water engineering-related factors (e.g. Water losses). The method also considered a number of factors, such as unexpected and extreme temperature changes, and forecasting factors studied by the Ethiopian Ministry of Water and Energy. The projected population in the subbasin is estimated at 2.52 million, so the total projected water supply demand i.e., for domestic, non-domestic, industrial, commercial, public, and institutional is approximately 126.53 MCM/yr by 2050. Our results revealed how changes in both climatic and socioeconomic factors strongly influence future water resource system performance, and this will help the water services provider better prioritize the refurbishment of existing infrastructure and investment in new infrastructure, and more importantly, manage the subbasin effectively by introducing resilient adaptation options.

Application of Sustainability Index of Tidal River Management (SITRM) in the Lower Ganges–Brahmaputra–Meghna Delta

The sustainability index (SI) is a relatively new concept for measuring the performance of water resource systems over long time periods. The purpose of its definition is to provide an indication of the integral behavior of the system with regard to possible undesired consequences if a misbalance in available and required waters occurs. Therefore, the tidal river management (TRM) approach has been implemented for the past three decades (from 1990 to 2020) within the polder system in Southwest Bangladesh to achieve water sustainability. TRM plan and watershed management plan (WMP) have commonalities as both are aimed at ensuring the sustainable use of watershed resources with the management of land, water, and the wider ecosystem of the watershed in an integrated way. The TRM plan focuses mostly on coastal regions, whereas the WMP focuses on both coastal and non-coastal regions. According to this, the aim of this study was to explore the application of the sustainability index of tidal river management (SITRM) in measuring the sustainability of tidal river management in the coastal area of the Lower Ganges–Brahmaputra–Meghna (GBM) delta. In order to quantify the sustainability of tidal river management, this research first provided the components and indicators of SITRM for the coastal region. The study follows a 5-point Likert scale for opinion survey of key informants and comprises households’ survey of farmers. In addition, it includes Landsat satellite images from Earth Explorer of the United States Geological Survey (USGS) and direct field observation to collect information regarding the indicators of SITRM. The study measures the index value of SITRM for identifying the water sustainability of Beel East Khukshia-TRM. The index value was 71.8 out of 100, showing good tidal river management for the Hari–Teka–Bhadra catchment. To achieve water sustainability and aid stakeholders and water managers in decision making, it may be possible to include the SITRM framework in tidal river management projects. In addition, the SITRM is more capable of facing drainage congestion, waterlogging, and climate change issues than watershed sustainability index (WSI), Canadian water sustainability index (CWSI), West Java water sustainability index (WJWSI), and water poverty index (WPI). Therefore, water professionals and policymakers can apply SITRM to assess the resilience of specific TRM schemes for greater sustainability in different coastal regions of the world.

Technical note: Statistical generation of climate-perturbed flow duration curves

Abstract. Assessing the robustness of a water resource system's performance under climate change involves exploring a wide range of streamflow conditions. This is often achieved through rainfall–runoff models, but these are commonly validated under historical conditions with no guarantee that calibrated parameters would still be valid in a different climate. In this note, we introduce a new method for the statistical generation of plausible streamflow futures. It flexibly combines changes in average flows with changes in the frequency and magnitude of high and low flows. It relies on a three-parameter analytical representation of the flow duration curve (FDC) that has been proved to perform well across a range of basins in different climates. We rigorously prove that, for common sets of streamflow statistics mirroring average behaviour, variability, and low flows, the parameterisation of the FDC under this representation is unique. We also show that conditions applied to these statistics for a solution to exist are commonly met in practice. These analytical results imply that streamflow futures can be explored by sampling wide ranges of three key flow statistics and by deriving the corresponding FDC in relation to model basin response across the full spectrum of flow conditions. We illustrate this method by exploring in which hydro-climatic futures a proposed run-of-river hydropower plant in eastern Turkey is financially viable. Results show that, contrary to approaches that modify streamflow statistics using multipliers applied uniformly throughout a time series, our approach seamlessly represents a large range of futures with increased frequencies of both high and low flows. This matches expected impacts of climate change in the region and supports analyses of the financial robustness of the proposed infrastructure to climate change. We conclude by highlighting how refinements to the approach could further support rigorous explorations of hydro-climatic futures without the help of rainfall–runoff models.

Contribution of the requirements engineering to the evaluation of water resources systems efficiency

In the water resources sector, the need to adopt a new way of thinking based on a systemic approach and analysis is justified by several situations: very complex constraints that accompany the development of the sector, functional interactions between various planned developments and the multitude of actors and stakeholders involved. System engineering is a general methodological approach that encompasses all the appropriate activities to design, evolve and verify a system providing an economical and efficient solution to the needs of customers while satisfying the whole of stakeholders. Based on these concepts of size, the purpose of this paper is to apply the principles of systems engineering for the exploration and evaluation of Boughrara water resources system performance. This system located in the north-west of Algeria involves subsystems in constant interaction, namely mobilization, treatment, purification and transfer of water. Its performance takes into account a number of parameters: compliance with customer satisfaction objectives, system constraints, stakeholder role and responsibility for achieving system-wide objectives, and not relationship with sectors of activity.

A simple drought risk analysis procedure to supplement water resources management planning in England and Wales

AbstractThe current ‘Deployable Output’ approach for assessing water resources system performance in England and Wales is a practical, communicable means for assessing the adequacy of a water supply system and determining the relative benefits of proposed system enhancements. A recognised flaw with this approach is that it fails to characterise the severity of potential supply shortfalls, leading to mischaracterisation of risks and benefits associated with alternative candidate investments. Here, we propose a Monte Carlo procedure that could supplement the existing process by exposing the magnitude (% water demand unserved) and duration (number of days) of supply curtailments under a range of drought scenarios. The method is demonstrated using a realistic, stylised water resources system and a discrete number of infrastructure investments. Results demonstrate that vulnerability assessments can expose previously unidentified risks that might radically alter a planner’s estimate of the cost‐effectiveness of a particular investment.

River management response to multi‐decade changes in timing of reservoir inflows, Columbia River Basin, USA

AbstractAround the world, long‐term changes in the timing and magnitude of streamflow are testing the ability of large managed water resource systems constructed in the 20th century to continue to meet objectives in the 21st century. Streamflow records for unregulated rivers upstream of reservoirs can be combined with records downstream of reservoirs using a paired‐watershed framework and concepts of water resource system performance to assess how reservoir management has responded to long‐term change. Using publicly available data, this study quantified how the intra‐annual timing of inflows and outflows of 25 major reservoirs has shifted, how management has responded, and how this has influenced reliability and vulnerability of the water resource system in the 668,000 km2 Columbia River basin from 1950 to 2012. Reservoir inflows increased slightly in early spring and declined in late spring to early fall, but reservoir outflows increased in late summer from 1950 to 2012. Average inflows to reservoirs in the low flow period exceeded outflows in the1950s, but inflows are now less than outflows. Reservoirs have increased hedging, that is, they have stored more water during the spring, in order to meet the widening gap between inflows and outflows during the summer low flow period. For a given level of reliability (the fraction of time flow targets were met), vulnerability (the maximum departure from the flow target) was greater during periods with lower than average inflows. Thus, the water management system in this large river basin has adjusted to multi‐decade trends of declining inflows, but vulnerability, that is, the potential for excess releases in spring and shortfalls in summer, has increased. This study demonstrates the value of combining publicly available historical data on streamflow with concepts from paired‐watershed analyses and metrics of water resource performance to detect, evaluate, and manage water resource systems in large river basins.

How Important Are Model Structural and Contextual Uncertainties when Estimating the Optimized Performance of Water Resource Systems?

AbstractUncertainty in simulating water resource systems (WRSs) makes it difficult to assess how effective different water management decisions will be. Uncertainty in simulation models can undermine the credibility of simulation and optimization studies and the uptake of their results. We identify different sources of uncertainty in WRS models and find that structural uncertainty (i.e., around definition of interrelationships within the system) and contextual uncertainty (i.e., around definition of the system boundaries) are rarely considered when simulating and optimizing WRSs. We propose a methodology to quantify the effects of structural and contextual uncertainties on the estimated performance of optimized water management decisions and demonstrate that they have a significant impact on a real‐world case study of a pumped‐storage system in the UK. To the best of the authors' knowledge, this is the first study to consider the impact of these types of uncertainty on optimized operating policies and their simulated performances. Our main finding is that of all the considered uncertainties, the assumptions made about context—specifically around the level of cooperation between neighboring water companies—had the greatest impact on performance estimates. This is important because few WRSs exist in isolation, yet discussion of the effects that a given definition of the system boundaries have on the simulation/optimization results is uncommon. We also highlight the significance of adequately considering aleatory uncertainty when evaluating performance estimates—something that few studies do—and present a simple technique to justify the sample size used for the evaluation of optimization results.

An Extension of the Sustainability Index Definition in Water Resources Planning and Management

The sustainability index (SI) is a relatively new concept for measuring the performance of water resource systems over long time periods. Its definition is aimed at providing an indication of the integral behaviour of the system with regards to possible undesired consequences if misbalance of available and required waters occurs. SI is initially defined as a product and later reformulated as a geometric mean of performance indicators: reliability, resilience and vulnerability. As an extension of a recently published methodology to compute and use SI, in this paper we propose introducing two more indicators of system performance: (1) reliability of annual firm (safe) water as a system yield and (2) deviation of reservoir levels from corresponding rule curves. The last indicator is of particular importance if there are multi-purpose reservoirs in the system because reservoirs are the most important and sensitive regulators of the water regime within the system. We also propose a framework for assessing system performance in a systematic manner to compute SI at various locations within the system if different operating strategies are applied and, finally, how to evaluate strategies according to the resulting SI by using multi-criteria methods. A case study example from Serbia is used to illustrate the results of measuring sustainability under alternative operating scenarios for a system with three reservoirs and two diversion structures.

Climate-induced alteration of hydrologic indicators in the Athabasca River Basin, Alberta, Canada

The hydrologic response of the Athabasca River Basin (ARB) in Alberta to projected changes in the future climate is investigated using the Variable Infiltration Capacity (VIC) process-based and distributed hydrologic model. The model forcings are derived from a selected set of GCMs from the latest Coupled Model Intercomparison Project (CMIP5) statistically downscaled to a higher resolution (10km) over Canada. Twelve hydrologic indicators that represent the magnitude and timing of the hydrologic regimes are evaluated for three 30-year time periods centered at the 1990s, 2050s and 2080s to identify significant alterations of hydrologic regimes between the reference and the two future periods using a t-test at 5% significance level. Hydrologic alteration factors (HAF) are also evaluated for each hydrologic indicator using the range of variability approach (RVA) to investigate projected changes in the distribution of these indicators. The results show increases in spring and winter flows for the two future periods at all hydrometric stations within the basin, resulting in an extended period of spring freshet. A higher rate of increase is projected for the stations located at the upper reach of the river because of the combined effects of increased precipitation and earlier snowmelt resulting from a warming climate. By contrast, summer flows are projected to decrease by up to 21% on average in the 2080s over most of the mainstem stations because of earlier snowmelt, increased evapotranspiration and no significant increase in summer precipitation. A water-management rule that optimizes impacts of water withdrawal from the lower reach of the Athabasca River under the current condition is also applied to the future scenarios to assess its relative performance under the projected climate conditions. The results indicate possible improvement in the water resources system performance in terms of increased reliability and resilience and reduced vulnerability during the two future periods as compared with those in the reference period mainly because of the projected increases in spring and winter flows, which has the potential to offset an expected future water deficit.

A bottom‐up approach to identifying the maximum operational adaptive capacity of water resource systems to a changing climate

AbstractMany water resource systems have been designed assuming that the statistical characteristics of future inflows are similar to those of the historical record. This assumption is no longer valid due to large‐scale changes in the global climate, potentially causing declines in water resource system performance, or even complete system failure. Upgrading system infrastructure to cope with climate change can require substantial financial outlay, so it might be preferable to optimize existing system performance when possible. This paper builds on decision scaling theory by proposing a bottom‐up approach to designing optimal feedback control policies for a water system exposed to a changing climate. This approach not only describes optimal operational policies for a range of potential climatic changes but also enables an assessment of a system's upper limit of its operational adaptive capacity, beyond which upgrades to infrastructure become unavoidable. The approach is illustrated using the Lake Como system in Northern Italy—a regulated system with a complex relationship between climate and system performance. By optimizing system operation under different hydrometeorological states, it is shown that the system can continue to meet its minimum performance requirements for more than three times as many states as it can under current operations. Importantly, a single management policy, no matter how robust, cannot fully utilize existing infrastructure as effectively as an ensemble of flexible management policies that are updated as the climate changes.

An inverse approach to perturb historical rainfall data for scenario-neutral climate impact studies

Summary Scenario-neutral approaches are being used increasingly for climate impact assessments, as they allow water resource system performance to be evaluated independently of climate change projections. An important element of these approaches is the generation of perturbed series of hydrometeorological variables that form the inputs to hydrologic and water resource assessment models, with most scenario-neutral studies to-date considering only shifts in the average and a limited number of other statistics of each climate variable. In this study, a stochastic generation approach is used to perturb not only the average of the relevant hydrometeorological variables, but also attributes such as the intermittency and extremes. An optimization-based inverse approach is developed to obtain hydrometeorological time series with uniform coverage across the possible ranges of rainfall attributes (referred to as the ‘exposure space’). The approach is demonstrated on a widely used rainfall generator, WGEN, for a case study at Adelaide, Australia, and is shown to be capable of producing evenly-distributed samples over the exposure space. The inverse approach expands the applicability of the scenario-neutral approach in evaluating a water resource system’s sensitivity to a wider range of plausible climate change scenarios.

Adaptive Reservoir Operation Rules Under Climatic Change

Increases in greenhouse gases caused by human activities have raised global temperature. Global warming affects water resources systems and the hydrologic cycle and may impact the performance of water resource systems. Water resources managers face challenges balancing conflicting goals in reservoir operation given the uncertainties introduced by climatic change. The HadCM3 climate model is used in this paper to estimate temperature and precipitation for early (2025–2039), middle (2055–2069) and late (2085–2099) periods of the 21st century under the A2 greenhouse gases emission scenario. The estimated temperature and precipitation from the climate model are input to a calibrated hydrologic model (IHACRES) to simulate inflow in a river basin draining to the Karoon-4 reservoir in Iran. A meta-heuristic multi-objective optimization algorithm (NSGA-II) is used in conjunction to predicted hydrologic variables to optimize dynamic operation rules in the Karoon-4 reservoir. The Karoon4 reservoir is operated non-adaptively and adaptively under climatic change. Our results show that adaptive reservoir management increases the reliability and reduces the vulnerability associated with hydropower generation in early, middle, and late simulation periods of the 21st century. These findings establish the importance of factoring in climatic change and considering adaptive strategies in future reservoir operations.

Paleo-reconstructed net basin supply scenarios and their effect on lake levels in the upper great lakes

Paleo-reconstructed hydrologic records offer the potential to evaluate water resources system performance under conditions that may be more extreme than seen in the historical record. This study uses a stochastic simulation framework consisting of a non-homogeneous Markov chain model (NHMM) to simulate the climate state using Palmer Drought Severity Index (PDSI)-reconstructed data, and K-nearest neighbor (K-NN) to resample observational net basin supply magnitudes for the Great Lakes of North America. The method was applied to generate 500 plausible simulations, each with 100 years of monthly net basin supply for the Upper Great Lakes, to place the observed data into a longer temporal context. The range of net basin supply sequences represents what may have occurred in the past 1,000 years and which can occur in future. The approach was used in evaluation of operational plans for regulation of Lake Superior outflows with implications for lake levels of Superior, Michigan, Huron and Erie, and their interconnecting rivers. The simulations generally preserved the statistics of the observed record while providing new variability statistics. The framework produced a variety of high and low net basin supply sequences that provide a broader estimate of the likelihood of extreme lake levels and their persistence than with the historical record. The method does not rely on parametrically generated net basin supply values unlike parametric stochastic simulation techniques, yet still generates new variability through the incorporation of the paleo-record. The process described here generated new scenarios that are plausible based on the paleo and historic record. The evaluation of Upper Great Lakes regulation plans, subject to these scenarios, was used to evaluate robustness of the regulation plans. While the uncertain future climate cannot be predicted, one can evaluate system performance on a wide range of plausible climate scenarios.

Linking climate projections to performance: A yield‐based decision scaling assessment of a large urban water resources system

AbstractDespite a decade of research into climate change impacts on water resources, the scientific community has delivered relatively few practical methodological developments for integrating uncertainty into water resources system design. This paper presents an application of the “decision scaling” methodology for assessing climate change impacts on water resources system performance and asks how such an approach might inform planning decisions. The decision scaling method reverses the conventional ethos of climate impact assessment by first establishing the climate conditions that would compel planners to intervene. Climate model projections are introduced at the end of the process to characterize climate risk in such a way that avoids the process of propagating those projections through hydrological models. Here we simulated 1000 multisite synthetic monthly streamflow traces in a model of the Melbourne bulk supply system to test the sensitivity of system performance to variations in streamflow statistics. An empirical relation was derived to convert decision‐critical flow statistics to climatic units, against which 138 alternative climate projections were plotted and compared. We defined the decision threshold in terms of a system yield metric constrained by multiple performance criteria. Our approach allows for fast and simple incorporation of demand forecast uncertainty and demonstrates the reach of the decision scaling method through successful execution in a large and complex water resources system. Scope for wider application in urban water resources planning is discussed.

Performance evaluation of a water resources system under varying climatic conditions: Reliability, Resilience, Vulnerability and beyond

Summary As introduced by Hashimoto et al. (1982), Reliability, Resilience, and Vulnerability (RRV) metrics measure different aspects of a water resources system performance. Together, RRV metrics provide one of the most comprehensive approaches for analyzing the probability of success or failure of a system, the rate of recovery (or rebound) of a system from unsatisfactory states, as well as quantifying the expected consequence of being in unsatisfactory states for extended periods. Assessing these comprehensive metrics at current (baseline) and future scenarios provide insight into system performance in changing or varying climatic conditions. Such an approach makes it possible to analyze different scenarios that could include specific mitigation or adaptation strategies to accommodate a varying climate. The method requires a subjective decision defining what constitutes an “unsatisfactory state” depending on acceptable risks. The application of this methodology is demonstrated using Tampa Bay Water’s Enhanced Surface Water System. In this case, for each scenario, a thousand ensembles of 300-years of monthly stream flow traces were first generated by a multi-site rainfall/runoff model. Second, a novel nonlinear disaggregation algorithm was developed to translate monthly outputs into daily values. The daily stream flow traces and their derivatives are then used to drive complex operational models that produce several system variables (e.g., permitted river withdrawals, reservoir storage volumes, and treatment plant production rates) at different locations. Outputs from the operational model were then used to define criteria over which the RRV and other metrics were evaluated. Several mitigation scenarios such as treatment and reservoir capacity expansion, as well as adaptation through operational changes were considered to evaluate system performance under varying climatic conditions. The approach highlights the benefits of comprehensive system performance metrics that are easy to understand by decision makers and stake holders and demonstrates the implementation of seemingly intractable ensemble size and simulation length in a distributed computing environment.

Modeling stakeholder‐defined climate risk on the Upper Great Lakes

Climate change is believed to pose potential risks to the stakeholders of the Great Lakes due to changes in lake levels. This paper presents a model of stakeholder‐defined risk as a function of climate change. It describes the development of a statistical model that links water resources system performance and climate changes developed for the Great Lakes of North America. The function is used in a process that links bottom‐up water system vulnerability assessment to top‐down climate change information. Vulnerabilities are defined based on input from stakeholders and resource experts and are used to determine system performance thresholds. These thresholds are used to measure performance over a wide range of climate changes mined from a large (55,590 year) stochastic data set. The performance and climate conditions are used to create a climate response function, a statistical model to predict lake performance based on climate statistics. This function facilitates exploration and analysis of performance over a wide range of climate conditions. It can also be used to estimate risk associated with change in climate mean and variability resulting from climate change. Problematic changes in climate can be identified and the probability of those conditions estimated using climate projections or other sources of climate information. The function can also be used to evaluate the robustness of a regulation plan and to compare performance of alternate plans. This paper demonstrates the utility of the climate response function as applied within the context of the International Upper Great Lakes Study.

Daily Time-Step Refinement of Optimized Flood Control Rule Curves for a Global Warming Scenario

Pacific Northwest temperatures have warmed by 0.8°C since 1920 and are predicted to increase in the 21st century. Streamflow timing shifts associated with climate change would degrade the water resources system performance for climate change scenarios using existing system operation policies for the Columbia River Basin. To mitigate the hydrologic impacts of anticipated climate change on this complex water resource system, optimized flood control operating rule curves were developed at a monthly time step in a previous study and were evaluated with a monthly time-step simulation model. Here, a daily time-step simulation model is used over a smaller portion of the domain to evaluate and refine the optimized flood-control curves derived from monthly time-step analysis. Daily time-step simulations demonstrate that maximum evacuation targets for flood control derived from the monthly analysis were remarkably robust. However, the evacuation schedules for Libby and Duncan Dams from February to April conflicted with Kootenay Lake level requirements specified in the 1938 International Joint Commission Order on Kootenay Lake. We refined the flood rule curves derived from monthly analysis by creating a gradual evacuation schedule, keeping the timing and magnitude of maximum evacuation the same as in the monthly analysis. After these refinements, the performance at monthly timescales reported in our previous study proved robust at daily timescales. Owing to a decrease in July storage deficits, additional benefits such as more revenue from hydropower generation and more July and August outflow for fish augmentation were observed when the optimized flood-control curves were used for a climate-change scenario.

Water Resources Implications of Global Warming: A U.S. Regional Perspective

The implications of global warming for the performance of six U.S. water resource systems are evaluated. The six case study sites represent a range of geographic and hydrologic, as well as institutional and social settings. Large, multi-reservoir systems (Columbia River, Missouri River, Apalachicola-Chatahoochee-Flint (ACF) Rivers), small, one or two reservoir systems (Tacoma and Boston) and medium size systems (Savannah River) are represented. The river basins range from mountainous to low relief and semi-humid to semi-arid, and the system operational purposes range from predominantly municipal to broadly multi-purpose. The studies inferred, using a chain of climate downscaling, hydrologic and water resources systems models, the sensitivity of six water resources systems to changes in precipitation, temperature and solar radiation. The climate change scenarios used in this study are based on results from transient climate change experiments performed with coupled ocean-atmosphere General Circulation Models (GCMs) for the 1995 Intergovernmental Panel on Climate Change (IPCC) assessment. An earlier doubled-CO2 scenario from one of the GCMs was also used in the evaluation. The GCM scenarios were transferred to the local level using a simple downscaling approach that scales local weather variables by fixed monthly ratios (for precipitation) and fixed monthly shifts (for temperature). For those river basins where snow plays an important role in the current climate hydrology (Tacoma, Columbia, Missouri and, to a lesser extent, Boston) changes in temperature result in important changes in seasonal streamflow hydrographs. In these systems, spring snowmelt peaks are reduced and winter flows increase, on average. Changes in precipitation are generally reflected in the annual total runoff volumes more than in the seasonal shape of the hydrographs. In the Savannah and ACF systems, where snow plays a minor hydrological role, changes in hydrological response are linked more directly to temperature and precipitation changes. Effects on system performance varied from system to system, from GCM to GCM, and for each system operating objective (such as hydropower production, municipal and industrial supply, flood control, recreation, navigation and instream flow protection). Effects were generally smaller for the transient scenarios than for the doubled CO2 scenario. In terms of streamflow, one of the transient scenarios tended to have increases at most sites, while another tended to have decreases at most sites. The third showed no general consistency over the six sites. Generally, the water resource system performance effects were determined by the hydrologic changes and the amount of buffering provided by the system's storage capacity. The effects of demand growth and other plausible future operational considerations were evaluated as well. For most sites, the effects of these non-climatic effects on future system performance would about equal or exceed the effects of climate change over system planning horizons.

Sensitivity of reservoir operation performance to climatic change

The potential impacts of changing climatic conditions on the operational performance of water resource systems was investigated in this paper. A multi-site streamflow generation model was used to synthesize potential monthly flow sequences reflecting two different sets of climatic conditions. The generated data were subsequently employed as input to a reservoir operation model that was used to determine the reservoir response to the inflow resulting from the implementation of the reservoir operating policy. The performance of an example reservoir system, the Shellmouth Reservoir located in the Canadian province of Manitoba, was evaluated and compared for the two sets of conditions. The operational performance was evaluated in terms of the reliability of the system for meeting the three purposes of the actual reservoir. The reservoir performance was determined to be sensitive to the inflow data. The results indicate that climatic change has potentially important implications for the operation of the example reservoir system.