Flow Duration Curve Research Articles

Potensi Pembangunan Pembangkit Tenaga Mini Hidro (PLTM) pada Sungai Batang Kenaikan Kabupaten Pasaman Barat

Rivers that flow from hilly or mountainous areas can be used for various purposes including; sources of drinking water, irrigation, fisheries, power plants, and downstream shipping lanes. West Sumatra Province is mostly a mountainous area and has many rivers flowing east and west from the Barisan hills. This condition allows the development of hydroelectric power plants that utilize the head and discharge of rivers. One potential development of a mini hydro power plant (PLTM) is in Batang Panggang, which is located in Paraman Ampalu Village, Gunung Tuleh District, West Pasaman Regency. The potential for developing a PLTM on the Batang Panggang River is based on topographic conditions that allow for adequate head height and river flow that can produce electrical energy. For this reason, it is necessary to study the potential by selecting the planned discharge so that it can produce several power production values. These various power productions can be taken into consideration in relation to development costs and operating patterns agreed with PT. PLN (Persero). In this study, the data used includes daily discharge data from automatic water level record (AWLR) recording over the last 15 years. From the discharge data, a Flow Duration Curve (FDC) can be drawn to determine the relationship between discharge and the probability of its occurrence, and this is used as a basis for selecting generator discharge plans and annual energy production. Based on the topographic conditions of the location, the elevation of the lighthouse weir is planned at an altitude of +200 m above sea level, the calming tank is at an altitude of +197 m and the location of the power house is at an altitude of +150 m, while the length of the carrier channel is 2400 m. From this elevation, the height of the fall, H, is 50 m. Assuming the effective fall height, Heff is 90%xH, then Heff is obtained as 45 m. By trying the planned discharge used is Q40% to Q80%, from the FDC we get Q40% = 17.97 m3/s, Q50% = 14.99 m3/s, Q60% = 12.98 m3/s, Q70% = 11.17 m3/s, and Q80% = 9.54 m3/s. Based on the fall height and design discharge, the appropriate type of turbine is a French turbine and the generator efficiency is 0.95, then the annual energy for each Qplan is obtained, namely; W40 = 40413.97 MWh, W50 = 37108.22 MWh, W60 = 34744.17 MWh, W70 = 31296.90 MWh, and W80 = 27606.57 MWh.

Environmental flow assessment, evaluation, and suggestions for dying riverine ecosystem of the transboundary Amudarya River, Central Asia

The Amudarya River (ADR) is the largest source of freshwater in Central Asia providing livelihood to millions of people by extracting water for agriculture. However, the over-exploitation has created some critical environmental issues. For example, almost no water for the delta and the Aral Sea, which was once the 4th largest lake in the world. The present study focused on the assessment of environmental flow requirements (E-flows) in the basin. However, the main challenges in the accomplishment were the unavailability of natural streamflow, which is necessary for E-flow assessment, and sparse and limited hydroclimatic data. A hydrologic model was configured to simulate naturalized streamflow using the meteorological data from the Climate Research Unit. Four hydrological methods (i.e., Tennant, low flow index (7Q10), flow duration curve analysis (Q90, and Q95), and flow duration curve shifting (FDCS)) and all-method mean were applied to estimate E-flows at 34 sites on all tributaries of the ADR. According to FDCS, 7Q10, Q90, and Q95, E-flows should be 46%, 37%, 30%, and 25% of naturalized mean annual flow (NMAF), respectively, and on average, it should be 35% of NMAF, assessed by the all-methods mean. For low-flow (October–March) and high-flow (April–September) months, E-flows were determined to be 20–30% and 40–98% of NMAF, respectively. E-flow evaluation with the current environmental conditions showed very serious concerns because no sites met the environmental flow requirements below Kerki. This study will be guidelines to improve the riverine ecosystem and for future sustainable development in the region.

Potential for small hydropower development on the Pumpum River of Ghana using Remote Sensing and Soil Water Assessment Tool

This study focused on identifying potential locations for the implementation of Small Hydropower Systems to enhance the existing energy infrastructure in the Pumpum River Basin (PRB). Utilizing remote sensing and the Soil and Water Assessment Tool, basin parameters were generated and simulated for hydropower analysis. The energy potential of suitable sites was assessed through flow duration curves and power duration curves. The findings reveal that the PRB exhibits potential for small hydropower development, identifying nine sites along the river. The results of the model indicate power capacities of 1,521 kW for the Run of River and 2,290 kW for the dam sites respectively. The most promising hydropower sites were identified as dam site 1, river of run site 1, and dam site 6 with corresponding firm power of 2356.2 kW, 1567 kW and 264 kW, resulting in estimated firm energy production of 12.07 GWh, 8.03 GWh, and 1.35 GWh, respectively. Considering the suitable spacing of more than between 12 km among dam site 1, river of run site 1, and dam site 6 and a combined annual energy production of 21.65 GWh, a recommended approach involves establishing a cascade hydropower arrangement at sites dam site 1, river of run site 1, and dam site 6 along the Pumpum River. With a plant capacity of 65% to 90% dependability range, incorporating an installed Francis turbine, the total annual firm energy that can be produced from the nine (9) (Run of river and dam) projected sites ranges between 0.69 and 12.07 GWh.

Combining Hydrological Modeling and Regional Climate Projections to Assess the Climate Change Impact on the Water Resources of Dam Reservoirs

Climate change may significantly impact the availability and quality of water resources in dam reservoirs by potentially altering the hydrological regime of lake tributaries and the corresponding flow–duration curves. Hydrological models driven by climate projections (downscaled to the watershed scale and bias corrected to eliminate systematic errors) are effective tools for assessing this potential impact. To assess the uncertainty in future water resource availability, resulting from the inherent uncertainty in climate model projections, an ensemble of climate models and different climate scenarios can be considered. The reliability and effectiveness of this approach were illustrated by analyzing the potential impact of climate change on the water availability at Brugneto Lake in northern Italy. This analysis was based on climate projections derived from an ensemble of 13 combinations of General Circulation Models and Regional Climate Models under two distinct scenarios (RCP4.5 and RCP8.5). The semi-distributed HEC-HMS model was adopted to simulate the hydrological response of the basin upstream of the lake. The hydrological model parameters were calibrated automatically via the PEST software package using the inflows to the lake, estimated through a reverse level pool routing method, as observed values. Future water availability was predicted for short- (2010–2039), medium- (2040–2069), and long-term (2070–2099) periods. The results indicate that the uncertainty in reservoir inflow is primarily due to the uncertainty in future rainfall. A moderate reduction in water availability is expected for Brugneto Lake by the end of the current century, accompanied by modifications in the flow regime. These changes should be considered when planning future adaptation measures and adjusting reservoir management rules.

Which range of streamflow data is most informative in the calibration of an hourly hydrological model?

ABSTRACT From which part of the streamflow time series does a hydrological model learn most about the behaviour of a catchment? How does this part change with the objective function used for model calibration? We calibrated the hourly model GR4H (Génie Rural à 4 paramètres au pas de temps Horaire) on data subsets selected based on the flow duration curve, which narrowed the range of streamflow that influenced the identification of model parameters the most. Using 658 catchments in the United States and France, we found that calibrating GR4H on the highest 50% of streamflow values of a given period provided similar parameters to calibration on the whole period, with the top 10% dominating the identification of parameters. The logarithmic transformation of streamflow balanced the contribution from high and low flows, but only the reciprocal transformation emphasized low flows. The proposed methodology identifies the informative ranges of streamflow data and allows anticipating potential model failures in nonstationary hydroclimatic conditions.

Regionalization of flow duration curves for catchments in southern India using a hierarchical cluster approach

Abstract The present study on the hydrologic regionalization was taken up to evaluate the utility of hierarchical cluster analysis for the delineation of hydrologically homogeneous regions and multiple linear regression (MLR) models for information transfer to derive flow duration curve (FDC) in ungauged basins. For this purpose, 50 catchments with largely unregulated flows located in South India were identified and a dataset of historical streamflow records and 16 catchment attributes was created. Using selected catchment attributes, three hydrologically homogenous regions were delineated using a hierarchical agglomerative cluster approach, and nine flow quantiles (10–90%) for each of the catchments in the respective clusters was derived. Regionalization approach was then adopted, whereby using step-wise regression, flow quantiles were related with readily derived basin-physical characteristics through MLR models. Cluster-wise performance analysis of the developed models indicated excellent performance with an average coefficient of determination (R2) values of 0.85, 0.97, and 0.8 for Cluster-1, -2, and -3, respectively, in comparison to poor performance when all 50 stations were considered to be in a single region. However, Jackknife cross-validation showed mixed performances with regard to the reliability of developed models with performance being good for high-flow quantiles and poor for low-flow quantiles.

Integrated hydrological modelling of two contrasting watersheds with a terminal reservoir in the Upper Tapi River basin, India

Abstract The present study developed an integrated hydrologic model for sustainable utilisation and water management in two complex watersheds with varying physioclimatic features and reservoirs. The soil and water assessment tool (SWAT) is used for predicting integrated inflows into the Hatnur reservoir from the Burhanpur and Purna watersheds of the Upper Tapi River basin, while outflows are simulated using a rule curve. The influence of watershed complexities on hydrological model parameters and the watershed processes are investigated using extensive multisite and multivariable calibration (1998–2007) and validation (2008–2013) approaches, including sensitivity and uncertainty analyses. The sensitive parameters are related to curve number (CN), groundwater, slope, and main channel characteristics. The annual streamflow (m3/km2/mm of rainfall) in the Burhanpur watershed is 568.7, which is 4.2 times higher than the Purna watershed's streamflow of 136.2. The hypsometric analysis, areal rainfall, and flow duration curves revealed a substantially different streamflow pattern and a larger coefficient of variation in the spatial distribution of water balance components over sub-watersheds in the Burhanpur watershed compared to the Purna watershed due to diverse topographic features. The developed model would be useful for planning controlled releases from the terminal reservoir to mitigate hazards in the downstream reaches of the Tapi River basin.

The Effect of Climate Change on the Hydropower Potential in the Kunhar River Watershed, Pakistan

Climate change plays a vital role in the hydrology of any river basin, which may have multidimensional consequences. There is a need to conduct climate change impact assessment studies with updated models and scenarios. This study aimed to assess the impact of climate change on the streamflow and hydropower in Pakistan’s Kunhar River basin. Three general circulation models (GCMs), under two Shared Socioeconomic Pathway scenarios (SSPs 2–45 and 5–85), the Soil and Water Assessment Tool, and the flow duration curve were used to project the change in climatic parameters, streamflow, and hydropower potential, respectively. The findings indicated that in the 2080s, the precipitation, maximum, and minimum temperatures are projected to increase by 10%, 2.0 °C, and 3.0 °C under the SSP 2–45 scenario and are projected to increase by 8%, 3.7 °C, and 4.4 °C under the SSP 5–85 scenario, respectively. The annual streamflow may increase by 15 to 11%, and the seasonal fluctuations are more likely to be dominant compared with the annual fluctuations. The hydropower potential will probably increase by 24 to 16% under the SSP 2–45 and 5–85 scenarios in the 2080s. However, seasonal changes in streamflow and hydropower may impact the hydropower plant operation in the basin. The Kunhar River’s hydrology may change from snow-fed to a rainfall–runoff river.

Parallelization of AMALGAM algorithm for a multi-objective optimization of a hydrological model

A calibration procedure is essential step to achieve a realistic model simulation particularly in hydrological model which simulates water cycle in the basin. This process is always faced with challenges due to selection of objective function and highly time-consuming. This study aimed to take advantage of parallel processing to accelerate the computations involved with simulation process of hydrologic model linked with the multi-objective optimization algorithm of AMALGAM for multi-site calibration of SWAT hydrologic model parameters. In order to illustrate how meaningful SWAT model calibration trade-off between the four objective functions involved in AMALGAM optimization program, the Pareto solution sets were provided. Furthermore, it is implemented a group of model runs with a number of cores involved (from one to eight) to demonstrate and evaluate the running of parallelized AMALGAM with taking advantages of “spmd” method to decrease the running time of the SWAT model. The results revealed the robustness of the method in reducing computational time of the parameter calibration significantly. This strategy with 4-objective functions focuses on high streamflow (Nash–Sutcliffe coefficient), low streamflow (Box–Cox transformed root–mean–square error), water balance (runoff coefficient error), and flashiness (slope of the flow duration curve error) provided an efficient tool to decide about the best simulation based on the investigated objective functions. This study also provides a strong basis for multi-objective optimization of hydrological and water quality models and its general analytical framework could be applied to other parts of the world.

Damming consequences: Quantifying the effects on channel geometry and floodplain inundation

Dams have a profound effect on floodplain inundation and channel geometry. Still, few studies have analyzed detailed channel geometry changes, especially as they affect downstream floodplain inundation on large rivers. This research compared the Apalachicola River depths and floodplain inundation downstream of the Jim Woodruff Dam between early and late post-dam periods. We used hydrographic data for 1960 and 2010 collected by the U.S. Army Corps of Engineers. A ≤1.2 point/m2 LiDAR point cloud covering the entire floodplain was fused with the hydrographic data. After a forward and inverse transformation between coordinate systems, the combined data was converted into a riverbed digital elevation model (DEM). River geometric properties were calculated (Area, channel width, mean depth, thalweg elevation, and width-to-mean-depth ratio) for 1960 and 2010. Daily discharge and stage data (1928–2020) were collected for Chattahoochee and Blountstown gauge stations. Eleven flows, between the 10th and 99th percentile extracted from the daily flow duration curve for early and late post-dam periods, were used in a 2D hydrodynamic model, Hydrologic Engineering Center's River Analysis System (HEC-RAS) to simulate floodplain inundation. The result reveals that the riverbed degraded by about 1.5 m near the dam. Geometric changes between early and late post-dam periods include upper reaches deepening and narrowing (mean depth changed from ∼6.0 to ∼7.3 m with a consistent width), while the lower reach exhibited shallowing and widening (mean depth went from ∼6.0 m to ∼5.0 m). The channel area generally increased between the periods. Inundation depth was reduced by ∼1.0 m, for most flow categories, and decreased by 15 % from 1960 to 2010 for similar flows between the periods, particularly for the upper and middle reaches. Floodplain inundation extent deacreased by about 24.1 % for flow of ∼513 m3/s. The inundation decreases was partly due to alteration in geometric properties. This study highlights the need for comprehensive river morphology assessments to address human-induced degradation, changing inundation patterns, and their global implications in similar riverine ecosystems.

Ecological flow research and optimal selection of the most ecologically relevant hydrologic indicators at the Jingjiang River's three outlets

Abstract Scientific ecological hydrological indicators provide constraints that contribute to the healthy operation and restoration of river ecosystems. Daily flow data from three Jing River outlets (SongZiKou (SZK), TaiPingKou (TPK), and OuChiKou (OCK)) spanning 1955–2019 were used. We employed innovative methods, such as IHA–RVA and annual distribution, to establish ecological flow thresholds. Surplus and deficit indicators were used to analyze annual and seasonal runoff dynamics. The PCA/RVA method identified relevant hydrological indicators and assessed hydrological changes influenced by the Three Gorges Reservoir (TGR). Key findings include suitable ecological flow thresholds for the flood season (SZK/TPK/OCK – 218.6/94.5, 51.7/96.0, and 60.9–4,494.5 m3/s, respectively). The TGR impacted the flow duration curve, causing deficits during the flood season (up to 0.99, OCK) and surpluses in non-flood seasons (up to 5.04, OCK). The study assessed the Jing River watershed's response to hydrological changes, notably due to the reservoir's water storage and flow interruption during the dry season, revealing declining low pulse count (SDG) and duration (MTS) and increasing high pulse duration (GJP). This research employs innovative methods and hydrological indicators, enhancing understanding of Jing River watershed ecological hydrology, and offering essential data for water resource management and ecosystem health.

Effect of dam construction on changes in river's environmental flow (case study: Gorganrood river in the south of the Caspian Sea)

Human activities such as dam construction can lead to significant river flow regime changes and, consequently, river environments and habitats. Different approaches for estimating the environmental flow have developed to improve the river ecosystem's environmental and habitat conditions. The hydrological approach is considered in many studies to estimate environmental flows considering its advantages. Vimba vimba persa is an economically and ecologically valuable species in the Caspian Sea that spawns and reproduces naturally in the Gorganrood River downstream in April–May. After the construction of the Voshmgir dam on the Gorganrood River, the fish population has drastically reduced in recent decades. In this study, to investigate the effect of constructing the Voshmgir dam on the environmental flow of Gorganrood River, a wide range of hydrological methods, including Tennant, Tessman, Arkansas, Aquatic Base Flow, Flow Duration Curve, High Flow-Low Flow, and FDC Shifting have been used. Comparing the correlation between the mean monthly flow time series before and after the Voshmgir dam demonstrates remarkable changes, including Pearson (0.95 to 0.86), Spearman's rho (0.93 to 0.78), and Kendall's τ (0.78 to 0.61) as a consequence of dam construction. The results indicate that estimated environmental flow from Tennant (1.1, 3.4 to 1.3, 3.8 cms) and Aquatic Base Flow (0.5 to 1.8 cms) methods have led to inadequate estimation due to significant changes in flow in different months. The amount of environmental flow during April–May estimated from investigated methods indicates the dam negatively affected water allocation to meet the river downstream's ecological and environmental needs. The flow duration curve analysis confirms that the dam construction has caused the river flow to fluctuate significantly within the year. The dam construction has dramatically reduced the flow in April–May, a critical environmental and ecological season. The April–May period coincides with the river's flood season. The construction of the Voshmgir dam has caused the components of high flow in the environmental flow to face severe shortages.

A graphical non-parametric hydrologic alteration test using flow duration curves

ABSTRACT Utilizing annual flow duration curves (FDCs), the modified Mood’s median test (MMMT) was applied to quantiles of the median annual FDCs at 122 disturbed sites in the conterminous US. A simple graphical tool based on the MMMT was combined with a false discovery rate multiple comparison procedure to illustrate the field significance of hydrologic alteration over a wide range of streamflow conditions. Hydrologic disturbance was mostly caused by dams, although other forms of alteration were explored. In addition, 249 minimally regulated Hydro-Climatic Data Network (HCDN) sites were investigated to assess regional climatic drivers of hydrologic alteration. Results indicate that dams can have varying effects on the hydrologic regime, but generally impact low flows more often than high flows in the US. At HCDN sites, we observe significant changes to hydrologic regimes in many regions, especially to low and median flows in the upper midwestern and eastern US.

Impact of interbasin transfer hydroelectric project on downstream aquatic habitat

AbstractThe recent surge of anthropogenic activities like damming is causing a severe threat to the aquatic ecosystem. A scope of minimizing the degradation of biota exists by modifying the dam operation policy. This can be achieved by releasing a minimum environmental flow (EF), which further requires more scientific investigations. The present study investigated the impact of an interbasin transfer hydropower dam on the downstream habitat of an endangered fish species, Tor putitora, using an adaptive modelling framework. The framework consists of coupling a reservoir operation and a hydrodynamic model. This study analyses the scope of releasing different EFs from a hydropower dam to meet the environmental flow requirement (EFR) at downstream with satisfactory power production efficiency. The EFR was estimated using flow duration curve and Tennant's method. A lean period inflow hydrograph was incorporated into the model with a series of alternate EFs. Two scenarios were explored, with 4 and 6 h of peaking hours, along with the three cases of different initial reservoir storage. The total usable area over the river reach of the mentioned fish species was evaluated from the flow parameters simulated by the hydrodynamic component of the model. The power production efficiencies and area utilization rates were assessed in all these cases to prepare an easy‐to‐use decision support tool in a tabular form depicting the possible states of EF. The generalized methodology adopted in this analysis will help the decision‐makers quantify EF to be released from the dam within an acceptable power generation efficiency.

A geostatistical approach to estimate flow duration curve parameters in ungauged basins

Flow duration curve represents the percentage of time that a river flow is equal to or greater. As these curves provide a direct response to the behavior of water resources in a basin, which is used widely in hydropower projects, it is important to predict flow duration curves in no metering basins, named “ungagged basins.” The geostatistical approach to predict the values of these curves in non-measured stations shows the expansion of the range of studies in this topic. The aim of this study is to predict the flow duration curve over long periods of time in a basin with ungauged regions using probability kriging, inverse distance weighting (IDW) and maximum likelihood (ML) methods. Flow data from 38 flow measuring stations in the Dez Basin were used to map different discharges of the flow duration curve, and as a result, in order to complete their values, zone and quantify them, three different values of Q10, Q50 and Q90 of the flow duration curve acquired. The results show that as the flow rate increases (or the time percentage decreases), the amount of computational error increases and in all cases, the probability kriging method has a smaller error (0.96) than the IDW (1.65) and ML (1.15) methods.

Evaluation of reservoir-induced ecological flow with consideration of ecological responses to multiple hydrological alterations: A case study in the Feiyun River Basin, China

With rapid economic and social development, human activities, such as the construction of reservoirs, have satisfied many needs. However, these activities have also caused changes in the hydrological ecosystem of the basin, impacting river biodiversity. The establishment of the Shanxi Reservoir within the Feiyun River Basin has inevitably altered the hydrological system, which was previously shaped primarily by precipitation. This study comprehensively evaluates the impact of Shanxi Reservoir on the hydrological alteration of the basin. Two ecological flow indicators, ecosurplus and ecodeficit, were used based on flow duration curves, along with the Shannon Index of river biodiversity (SI) and several hydrological indicators: the Indicator of Hydrological Alteration (IHA), the Degree of Integrated Hydrological Alteration (D0), and the Dundee Hydrological Regime Alteration Method (DHRAM). The results of the study show that: (1) the previously observed correlation between ecological flow and precipitation was disrupted following the construction of the reservoir. As a result, there was a notable ecological deficit in the spring season, with a maximum of 0.43, and a considerable increase in ecological surplus during winter, reaching a maximum of 4.80. (2) The flow regime of the river has undergone significant changes, resulting in a combined hydrological variability of 66. 44% and an ecological hazard level of 4. This indicates a high risk to the river’s ecological environment. (3) The total seasonal ecological surplus has increased and remained consistently high, which has contributed to a decline in the SI of river biodiversity, the river's biology has degraded over time (4) The use of ecological flow indicators is closely tied to IHA32 indicators. Combining ecological flow indicators with ERHIs has shown to be a successful approach for assessing ecohydrological regimes. These findings have significant implications for future studies in similar cases and offer valuable guidance for managing water resources.

Hybrid model for daily streamflow and phosphorus load prediction.

Environmental factors, such as climate change and land use changes, affect water quality drastically. To consider these, various predictive models, both process-based and data-driven, have been used. However, each model has distinct limitations. In this study, a hybrid model combining the soil and water assessment tool and the reverse time attention mechanism (SWAT-RETAIN) was proposed for predicting daily streamflow and total phosphorus (TP) load of a watershed. SWAT-RETAIN was applied to Hwangryong River, South Korea. The hybrid model uses the SWAT output as input data for the RETAIN. Spatial, meteorological, and hydrological data were collected to develop the SWAT to generate high temporal resolution data. RETAIN facilitated effective simultaneous prediction. The SWAT-RETAIN exhibited high accuracy in predicting streamflow (Nash-Sutcliffe efficiency (NSE): 0.45, root mean square error (RMSE): 27.74, percent bias (PBIAS): 22.63 for test sets), and TP load (NSE: 0.50, RMSE: 423.93, PBIAS: 22.09 for test sets). This result was evident in the performance evaluation using flow duration and load duration curves. The SWAT-RETAIN provides enhanced temporal resolution and performance, enabling the simultaneous prediction of multiple variables. It can be applied to predict various water quality variables in larger watersheds.

Water Resources Assessment for Raw Water Purposes in Serang Watershed, Kulonprogro

One source of raw water for drinking water is river water. The raw water source for drinking water must meet the requirements for quantity, continuity, and quality. Raw water for drinking water must meet class I water quality requirements. This study aims to assess of the potential for water availability and water quality in the Serang River. Analysis of water availability used statistical methods and simulated rainfall-runoff with the HEC-HMS model. Calibration of the hydrological model was carried out in sub-watersheds where there were observational discharge data. Water availability is reviewed in the second-order river. Water quality status was analyzed using the Pollutant Index and Storet methods. The results of the analysis of water availability for reliable discharge with a probability of 80%, 90%, and 95% in several sections of the Serang River to order 2 rivers can be presented in the form of a flow duration curve. The results of the analysis of the status of water quality in several sections of the upstream Serang river based on the Storet method and the Polluter Index method show that in general, it is in a slightly polluted condition.

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.

Exploring Signature‐Based Model Calibration for Streamflow Prediction in Ungauged Basins

AbstractCalibration of precipitation‐streamflow models to streamflow signatures is a promising approach for streamflow prediction in ungauged basins (PUB). The estimation of parameter and prediction uncertainty in this case is not trivial because: (a) calibration takes place in the signature domain, while predictions are required in the time domain, and (b) streamflow signatures are estimated (e.g., from donor catchments) rather than “observed” (computed from observed streamflow in the target catchment), and therefore particularly uncertain. This study investigates model calibration using estimated signatures in an Approximate Bayesian Computation framework. First, we construct a stochastic signature transfer model, based on seasonal flow duration curves. Second, we calibrate a precipitation‐streamflow model to the estimated signatures, accounting for their uncertainty. The proposed method is tested in six catchments of the Thur basin, Switzerland. Three data availability scenarios are considered: (a) concomitant scenario, where signatures are “observed,” (b) non‐concomitant scenario, where signatures are transferred from a different time period, and (c) regionalization scenario, where signatures are transferred from (neighboring) donor catchments. In this study, the switch from observed to regionalized signatures increases predictive streamflow uncertainty by 38% and worsens the (deterministic) fit to observations by 17% (in terms of Nash‐Sutcliffe efficiency). Despite this deterioration, posterior predictive uncertainty remains lower than prior predictive uncertainty generated using uniform priors over representative parameter ranges (“uncalibrated” model), which demonstrates the effectiveness of the proposed signature‐based calibration. More importantly, uncertainty is reliably estimated at the ungauged catchments, which represents a key advance in stochastic streamflow PUB.