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Various methods for determining environmental flows can be based on hydrological characteristics, a combination of morphological and hydrological characteristics, or solely on hydraulic characteristics. Such methods may also be based on multi-criteria decision-making, where a low flow regime and its variability are considered. The methods for determining environmental flows as hydrological limits (sometime called desktop methods) are solely based on hydrological statistics and are believed to implicitly incorporate links to the state of river ecosystems. In the paper, we compared the performance of several methods in the set of the 137 official water balance inventory profiles of the Slovak Hydrometeorological Institute, which are evenly distributed over the territory of Slovakia. The analysis also accounted for the dependence between hydrological characteristics and environmental flow values. We also compared the frequency of the occurrence of their critical values (ecohydrological) in the reference periods 1931-1960 and 1991-2019. We proposed an intermediate system of regionalized relationships based on simple Tennant methods, which does not disturb the existing system of water allocations and uses in the water balance inventory. [ABSTRACT FROM AUTHOR]

This study explored the potential of three calibration approaches – single-site, multisite, and multisite–multivariable – to simulate the streamflow and sediment yield of the Upper Blue Nile (UBN) river basin using the Soil and Water Assessment Tool (SWAT). Several statistical indices were used to verify the SWAT model performance. While all three approaches reasonably estimate the streamflow and sediment yield, the multisite calibration approach was found to perform better in handling the spatial variability of parameters and their influence on streamflow and sediment yield over the entire catchment. Further, evaluations of hydropower potential at the selected location were conducted to demonstrate the importance of calibration approaches in planning and designing various water resource structures. [ABSTRACT FROM AUTHOR]

The article presents the characteristics of the Flow Duration Frequency (FDC) curve statistics of the Hornád River and its tributaries for a period of 60 years (1961-2020) and compares the flow duration curves divided into decades (1961-1970, 1971-1980, 1981- 1990, 1991-2000, 2001-2010 and 2011-2020). High flows corresponding to the flow of 10% (Q10) and 25% (Q25), medium flows corresponding to the flow of 50% (Q50) and low flows corresponding to the flow of 70% (Q75) and 90% (Q90) were analyzed. The study covered 7 catchments located in the Hornád river catchment (eastern Slovakia). The greatest variability of flows in individual decades in relation to the multi-year period 1961-2020 was recorded in all threshold ranges at the station in Prešov Sekčov. The highest values were recorded in the range of low flows (Q90), for which the coefficient of variation was 0.38 (Q90) and 0.27 (Q75). A high coefficient of variation Cv was also recorded for the Košické Olšany station in terms of low flows for Q75 and Q90, which were 0.21 and 0.19, respectively. At the remaining stations, the variability of Cv ranged from 0.08 to 0.15 for Q75 and Q90. The variability of high flows (Q10 and Q25) ranged from 0.11 to 0.17 for all catchments except for the Prešov Sekčov station, for which the values were 0.21 and 0.27, and Stratená 0.19 and 0.18, respectively.

ABSTRACT The objective of this study was to analyze the influence of climate change on the flow duration curves of five small rural catchments in the Amazon, as well as the hydroelectric power duration curves of micro hydroelectric power plants (MHPs) which can be implemented in the respective hydroelectric sites. The scenarios used were RCP 4.5 and RCP 8.5, defined during the 5th IPCC Report; these are the main optimistic and realistic greenhouse gas emission scenarios in the future. They projected on the flow duration curves of the small catchments under study and, consequently, on the hydroelectric power duration curves. Future precipitation was obtained via the PROJETA platform. For the simulation of flow duration curves, a rainfall-runoff model was used. The determination of the power duration curves was considered with the observed and simulated flow duration curves and with design parameters available in the literature. Based on the simulations, the reduction of high duration flows (minimum flows) was verified for the future scenarios studied, mainly for RCP 8.5, reflecting directly in the reduction of the hydro energetic potential of the analyzed rural catchments.

The article presents the characteristics of the Flow Duration Frequency (FDC) curve statistics of the Hornád River and its tributaries for a period of 60 years (1961-2020) and compares the flow duration curves divided into decades (1961-1970, 1971-1980, 1981-1990, 1991-2000, 2001-2010 and 2011-2020). High flows corresponding to the flow of 10% (Q10) and 25% (Q25), medium flows corresponding to the flow of 50% (Q50) and low flows corresponding to the flow of 70% (Q75) and 90% (Q90) were analyzed. The study covered 7 catchments located in the Hornád river catchment (eastern Slovakia). The greatest variability of flows in individual decades in relation to the multi-year period 1961-2020 was recorded in all threshold ranges at the station in Prešov Sekčov. The highest values were recorded in the range of low flows (Q90), for which the coefficient of variation was 0.38 (Q90) and 0.27 (Q75). A high coefficient of variation Cv was also recorded for the Košické Olšany station in terms of low flows for Q75 and Q90, which were 0.21 and 0.19, respectively. At the remaining stations, the variability of Cv ranged from 0.08 to 0.15 for Q75 and Q90. The variability of high flows (Q10 and Q25) ranged from 0.11 to 0.17 for all catchments except for the Prešov Sekčov station, for which the values were 0.21 and 0.27, and Stratená 0.19 and 0.18, respectively. [ABSTRACT FROM AUTHOR]

• A blueprint for calculating probabilistic future streamflow and flow duration curves in a mountainous cold region. • Integrating fine spatial and temporal resolution forcings from an atmospheric model (WRF) with a hydrological model (MESH) • A novel method to incorporate uncertainty from a regional (CanRCM4) climate model to perturb WRF Pseudo Global Warming. In cold regions, climate change, including warming and changes in snowmelt dynamics, have profound impacts on streamflow patterns, often leading to flooding events. Understanding the projected changes in hydrometeorological factors contributing to streamflow, such as snowmelt runoff and rain-on-snowmelt, is crucial for effective adaptation and mitigation strategies. It is also essential to consider uncertainty in streamflow projections and incorporate this uncertainty into flood predictions. This study presents a blueprint for calculating probabilistic future streamflow and flow duration curves in a mountainous cold region. The methodology integrated forcings from an atmospheric model (WRF) with a hydrological model (MESH) at fine spatial (4 km) and temporal (3-hourly) resolutions. To account for uncertainty, an ensemble of 15 CanRCM4 regional climate simulations with varying boundary conditions for the RCP 8.5 scenario was utilized. A novel method was developed to perturb the CanRCM4 simulations' precipitation using a WRF Pseudo Global Warming run to incorporate uncertainty. This comprehensive approach revealed significant uncertainty in streamflow driven by internal variability. WRF-driven simulations without uncertainty showed a decrease in future streamflow extremes, while the perturbed simulations demonstrated the potential for substantially higher values under climate change. Moreover, the study derived probabilistic flow duration curves from the streamflow projections, aiding in estimating flood frequency for floodplain mapping when driving local hydraulic models. The methodology developed in this work can be extended to other river basins in Canada and elsewhere where gridded downscaled climate model outputs are available. [ABSTRACT FROM AUTHOR]

Planning and management of water resource infrastructure requires a depth of knowledge on the characteristics of hydrological extremes, floods and droughts. Infrastructure design is traditionally based upon historically observed extreme events, assuming that they are independent and identically distributed (i.i.d.) and stationary, i.e. they fluctuate within a fixed envelope of variability. Information on historical hydroclimate provides a limited range of hydrological extremes, which rarely includes long-term worst droughts. This study demonstrates the application of a paleo-environmental dataset, 900 years of weekly streamflow stochastically derived from a tree-ring reconstruction of annual streamflow, to assess the hydrological drought risk. The historic and prehistoric hydrological drought characteristics, i.e. severity–duration–frequency (SDF) relationships, are evaluated. The results indicate that the severity and duration of hydrological drought with the same recurrence interval is substantially larger and longer than those observed over the 100-year historical period. Historic and prehistoric drought SDF relationships established in this study demonstrate the implications of non-stationary climate in the analysis of extreme droughts. Therefore, projected droughts of the 21st century may not exceed the drought severity found in the prehistoric record to the same extent that they exceed historical droughts in the instrumental record. This study emphasizes the importance of paleohydrology in comprehending the region's drought. HIGHLIGHTS The results from the study indicate that the drought characteristics over the past millennium differed substantially from those which occurred over the past century.; Defining drought response triggers based on the historical data alone could underestimate the potential drought severity.; Our results also indicate that it is irrational to assume stationary climate in determining the frequency of severe droughts.;

Flow duration curves (FDCs) that represent streamflow regime function through an empirical relationship between the FDC parameters and basin descriptors are widely adopted for hydrologic applications. However, the applications of this method are highly dependent on the availability of observation data. Hence, it is still of great significance to explore the process controls of underpinning regional patterns on streamflow regimes. In this study, we developed a new regionalization method of FDCs to solve the problem of runoff prediction for ungauged mountainous basins. Five empirical equations (power, exponential, logarithmic, quadratic, and cubic) were used to fit the observed FDCs in the 64 mountainous basins in eastern China, and the power model outperforms other models. Stepwise regression was used to explore the differentiated control of 23 basin descriptors on the 13 percentile flows of FDCs, and seven descriptors remained as independent variables for further developing the regional FDCs. Application results with different combinations of these selected descriptors showed that five indices, i.e., average annual rainfall (P), average elevation (H), average gradient (β), average topographic index (TI), and maximum 7d of annual rainfall (Max7d), were the main control factors of FDCs in these areas. Through the regional method, we found that 95.31% of all the basins have NSE values greater than 0.60 and ε (namely the relative mean square error) values less than 20%. In conclusion, our study can guide runoff predictions to help manage booming demands for water resources and hydropower developments in mountainous areas. [ABSTRACT FROM AUTHOR]

Climate change models for southern Africa predict less frequent, but more intense, rainfall events, and an increased frequency of tropical cyclones. With their steep topography and small catchments, headwater streams generate large floods following intense rainfall events. Large flooding events in headwater streams are under studied in southern Africa. In this paper, we explore flooding in the upper Klaserie River, Limpopo River System, South Africa, to determine the flow distribution and flood frequency for the catchment. In addition, we determine the return level for a large, economically damaging, flood generated following the landfall of a sub-tropical depression in January 2012 and, attempt to identify rainfall patterns that resulted in similar floods. An annual hydrological cycle with summer maxima and winter minima for both rainfall and flow was identified. The flood frequency analysis demonstrated that the January 2012 flood had an estimated return level of 225 years. This flood had a peak flowrate exceeding 1200 m3s-1 in a system with an average daily flowrate of 1 m3s-1. Regression tree analysis showed that a two-day rainfall in excess of 240 was a predictor for four of the five largest floods. A two-day rainfall in excess of 400 mm distinguished the January 2012 flood from other floods. Non-stationarity analyses for the flow and rainfall data and a SWAT hydrological model are recommend for the upper Klaserie River to evaluate climate and land cover changes, and their relationship to the magnitude of the 2012 flood. Our study demonstrates that South African river monitoring data can be used to detect and characterize major floods, despite deficiencies in these data. Continuation of these monitoring programs is vital for river health monitoring and the detection of trends in floods resulting from human activities and climate change. [ABSTRACT FROM AUTHOR]

The quantification of the consequences of climate change (CC) on the hydrology of the West Africa region was performed using a validated Hydrologiska Byrans Vattenbalansavdelning hydrological model and regional climate models which was driven by different general circulation models (GCMs) from the Coordinated Regional Downscaling Experiment (CORDEX) and the Regional Climate Division of the Institute of Meteorology and Climate Research at Karlsruhe Institute of Technology (IMK-IFU). The quantile mapping and linear-scaling bias adjustment methods were used to correct the inherent errors in the climate simulations. Flow duration curves (FDCs) and generic annual discharge cycles were used in determining the impacts of the change on hydrology (river flow) in the Black Volta catchment within the subregion. It was found out that, in the first segment of the FDCs representing high flows, there was a slight increase in the future flow characterizing a higher watershed water yield from high rainfall events in the future. The 10–40% exceedance probabilities of flow representing wet conditions; 40–60% relating to mid-range flows; 60–90% representing dry period conditions; and low flows (90–100%) all show a decrease in the future flows for four out of the five GCM driving models. Most worrying is the reduction in flows for the 90–100% exceedance probabilities in the future relating to the sustainability of streamflow in the long term. It was concluded that CC could negatively impact and decrease the hydrology of the subregion in the future with most of the rivers in the catchment running dry in most months of the annual discharge cycle. HIGHLIGHTS The study demonstrates the effectiveness of using simple and less data demanding tools in quantifying the hydrological consequences of climate change in the subregion.; We were able to bias correct the climate simulations using measured (observed) rainfall and temperature data as the ‘correct’ data.; We used two different correction methods in this study and their accompanying effects on the hydrology of the region.;

Drought has been among the priority issues for a long time because of its effects that vary depending on duration and severity. Hydrological drought can be explained as the decrease in clean water resources caused by climate change. In this paper, Arsuz Plain, one of the agricultural protected area in the Asi River Basin, was selected as the case study for the hydrological drought analysis. Firstly, discharge-time and flow duration curves (FDC) were created by using monthly average discharge data between the years of 1990 and 2015 which were obtained from three different Flow Observation Stations (FOSs) (numbered D19A021, D19A022 and D19A023), located close to each other. With the help of these data, Streamflow Drought Index (SDI) values were calculated for different time scales such as 3, 6 and 12 months. Consequently, it has been seen that all three stations have similar results in terms of the peak flow rate values excluding a few periods. As of 2000, it has been observed that Extreme Drought and Extremely Wet periods have started to occur in the basin for these stations. While the most wet period began between the years 2009 and 2010, the driest period was 2014. Considering the course of the drought event in different time scales, it can be concluded that the number of dry periods has increased in recent years.

Ugandan rivers are being tapped as a resource for the generation of hydropower in addition to other uses. Studies on the reliability of these hydropower plants due to climate and land-use/land cover changes on the hydrology of these rivers are scanty. Therefore, this study aimed to model the impact of the changing climate and land-use/cover on hydropower reliability to aid proper planning and management. The hydropower reliability of Muzizi River catchment was determined from its past (1998–2010) and midcentury (2041–2060) discharge at 30 and 95% exceedance probability under Representative Concentration Pathways (RCPs) of 4.5 and 8.5, respectively. The past and projected hydropower were compared to determine how future climate and land-use changes will impact the discharge and hydropower reliability of Muzizi River catchment. Six LULC scenarios (deforestation, 31–20%; grassland, 19–3%; cropland, 50–77%; water bodies, 0.02–0.01%; settlement, 0.23–0.37%, and Barren land 0.055–0.046% between 2014 and 2060) and three downscaled Regional Climate Model (REMO and RCA4 for precipitation and RACMO22T for temperature from a pool of four CORDEX (Coordinated Regional Climate Downscaling Experiment) Africa RCMs) were examined. A calibrated SWAT simulation model was applied for the midcentury (2041–2060) period, and a potential change in hydropower energy in reference to mean daily flow (designflow ≥ 30% exceedance probability), firm flow (flow ≥ 95% exceedance probability), and mean annual flow was evaluated under the condition of altered runoff under RCP4.5 and RCP8.5 climate change scenarios for an average of REMO and RCA4 RCM. The future land use (2060) was projected using the MOLUSCE (Module for Land Use Change Evaluation) plugin in QGIS using CA-ANN. Three scenarios have been described in this study, including LULC change, climate change, and combined (climate and LULC change). The results suggest that there will be a significant increase in annual hydropower generation capacity (from 386.27 and 488.1 GWh to 867.82 and 862.53 GWh under RCP4.5 and RCP8.5, respectively) for the combined future effect of climate and land-use/cover changes. Energy utilities need to put in place mechanisms to effectively manage, operate, and maintain the hydropower plant amidst climate and land-use change impacts, to ensure reliability at all times. HIGHLIGHTS Innovative approaches for hydrological modeling in data-scarce scenarios.; The possibility to utilize bias-corrected reanalysis and historical discharge data to build a climate model in data-scarce scenarios.; Sheds light on the potential risks of land-use and climate change on hydropower reliability in data scarcity areas.; Informs the need to implement prudent catchment management practices and develop policies.;

Agricultural irrigation projects require information on the quantity and frequency of streamflow to design irrigation systems. On the one hand, this information is obtained from gauging stations or hydrologic models. On the other hand, there are few gauging stations, and hydrologic models are expensive to implement, especially for small irrigation projects. This work proposes a method for estimating spatially distributed Flow Duration Curves (FDC), and describes the SanAntonioApp interactive application with open access and repository, which is used to share the results of this work. The proposed framework uses three years of records of a rich hydrometeorological network to implement, optimise and cross-validate the WFLOW-HBV distributed hydrologic model in San Antonio Creek (Salto, Uruguay). Then, FDC are generated by extending the simulation period with the long records of an agro-climatological station (30 years). The results of this work contribute to evaluate the water availability of the San Antonio catchment and provide information on how often this availability is guaranteed. In addition, the application allows estimating the probability of exceedance of the daily streamflow for a given month and location. This function could be used to estimate the environmental flow established in the current water regulation in Uruguay.

In developing countries with data scarcity challenges, an integrated approach is required to enhance the estimation of streamflow variability for the design of water supply systems, hydropower generation, environmental flows, water allocation and pollution studies. The Flow Duration Curve (FDC) was adopted as a tool that is influenced by topography, land use land cover, discharge and climate change. The data from Global Climate Model (GCM) projections, based on Representative Concentration Pathways (RCP) 4.5 and RCP 8.5 climate scenarios, were used as input data for the SWAT model for the simulation of streamflow. The FDCs were then derived from the simulated streamflow. The FDC for RCP 4.5 showed insignificant differences, whilst for RCP 8.5 it showed an increase of 5–10% in FDC from the baseline period, which is likely to increase the hydropower generation potential with some considerable streamflow variability. The integrated approach of utilizing FDC, GIS and SWAT for the estimation of flow variability and hydropower generation potential could be useful in data scarce regions. [ABSTRACT FROM AUTHOR]

Tropical regions are experiencing high rates of forest cover loss coupled with changes in the volume and timing of rainfall. These shifts can compromise streamflow and water provision, highlighting the need to identify how forest cover influences streamflow generation under variable rainfall conditions. Although rainfall is the key driver of streamflow regimes, the role of forests is less clear, particularly in tropical regions where forest loss is an ongoing risk. Forest cover loss alters evapotranspiration, rainfall infiltration and storage, and may increase stream ecosystem vulnerability to rainfall extremes. Puerto Rico, an island with spatially heterogenous forest cover and a marked geographic rainfall gradient, is projected to experience more frequent droughts and flash flooding. Using 15‐min streamflow data collected between 2005 and 2016 from 20 US Geological Survey stream gages and 3‐hourly Multi‐Source Weighted‐Ensemble Precipitation rainfall estimates, we utilized flow‐duration curves and linear mixed regression models to examine the role of forest cover in regulating the timing and volume of streamflow. The mixed model approach helps to account for differences in watershed characteristics. We determined the effects of rainfall and forest cover on low and peak flows in Puerto Rican streams, then evaluated changes in these relationships under dry and wet antecedent rainfall conditions. Watersheds with high forest cover had consistently greater low and peak streamflow than deforested ones under all rainfall conditions, although the effect was more marked during wet antecedent conditions, suggesting that peak flow is largely the result of saturation excess overland flow. During dry antecedent rainfall conditions, highly forested watersheds had higher streamflow than deforested ones, suggesting greater hillslope storage and release may also be at play. Our results demonstrate that forest cover generated a net increase in hillslope infiltration and storage and may lessen drought impacts on streamflow in Puerto Rico. Resilience to prolonged drought may be limited by finite water storage potential in this steep, mountainous setting, highlighting maintenance of forest cover as an important water management strategy to increase infiltration. [ABSTRACT FROM AUTHOR]

The impacts on global water resources may be more intense due to climate change, making access to water more difficult and, consequently, maintaining life. In the Amazon, the effect may be even worse, as it is one of the region’s most vulnerable to these changes. Thus, the objective is to analyze future variations in the volumes and duration curves of the flow of the Amazon River to verify the hydrological response to climate changes. The daily flows observed were from the database of the National Water Agency of Brazil. Future flow data was generated for the Representative Concentration Pathways (RCPs) 6.0 and 8.5 scenarios of the Global hydrological model WaterGAP2 forced by the General Circulation Models MIROC5 and HadGEM2-ES, obtained from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) platform. The flow duration curves of the base periods were created from the last 20 years of observed data for each flow meter station, as well as the simulated base period curves (2000–2019), to compare with the curves of future scenarios (from 2020). For a more punctual analysis, decadal volumes were also analyzed. WaterGAP2 was efficient, presenting the classification “very good” for most stations analyzed according to the adopted statistical indicators. Most of the extreme flows were observed from 2080 to 2099. For WaterGAP2 (MIROC5), in most stations, volumes were below the expected decadal average for the century generally from 2020 to 2059. Increasing again after 2060 for WaterGAP2 (HadGEM2-ES) projections, the volumes are usually close or below the decadal average, with a decrease from 2060 (generally for RCP 8.5). [ABSTRACT FROM AUTHOR]

In developing countries with data scarcity challenges, an integrated approach is required to enhance the estimation of streamflow variability for the design of water supply systems, hydropower generation, environmental flows, water allocation and pollution studies. The Flow Duration Curve (FDC) was adopted as a tool that is influenced by topography, land use land cover, discharge and climate change. The data from Global Climate Model (GCM) projections, based on Representative Concentration Pathways (RCP) 4.5 and RCP 8.5 climate scenarios, were used as input data for the SWAT model for the simulation of streamflow. The FDCs were then derived from the simulated streamflow. The FDC for RCP 4.5 showed insignificant differences, whilst for RCP 8.5 it showed an increase of 5–10% in FDC from the baseline period, which is likely to increase the hydropower generation potential with some considerable streamflow variability. The integrated approach of utilizing FDC, GIS and SWAT for the estimation of flow variability and hydropower generation potential could be useful in data scarce regions.

ABSTRACT The Atrato river basin is located in the Pacific fringe of Colombia, region with one of the highest precipitation rates in the world. The main purpose of this study is to determine the dominant processes in the hydrological responses along 17 sub-basins within the basin using principal component analysis. Watersheds located at the headwater presented a fast or medium response to the precipitation events, while higher flow homogeneity was observed in watersheds located at the lower portions of the basin. Three principal components were responsible for explaining 85.18% of the total variance. The component PC1 revealed the largest contributions for low flow behavior, being associated to precipitation, characteristic discharge values, compactness index, soil coverage and soil coarse textures. The component PC2 was assigned to the geological variables, fine and average texture soil and the average basin slope. Finally, the component PC3 has shown to be related to high flow patterns (maximum characteristic discharge values Q5 and Q1), igneous rocks and length of the basin. Highest specific discharge was associated to alluvial deposits and forest cover, whereas the slope was considered determinant for the run-off generation.

There are different methods in hydrological approach for estimating the environmental flow and a comparative assessment is necessary. The low flow indexes (7Q2 and 7Q10), Smakhtin, Tennent and flow duration curve were used to estimate the environmental flow of Zohreh River in the southwest of Iran. The Smakhtin, 7Q2, 7Q10 and Tennant methods resulted in the estimation of constant values of 27.2, 12.7, 5.9 and (8 and 24) cms, so that, on average 52.8, 26.9 and 12.3, 36.7 percent of the monthly flow is allocated to the environmental flow. The monthly environmental flow pattern for these methods does not fit well with the monthly flow pattern, and thus it can be concluded that the Smakhtin, 7Q2, 7Q10 and Tennant methods cannot be used in the initial form. The application of the flow duration curve leads to an environmental flow assessment in the range of 6.8–38 cms in different months, whose time pattern completely matched with the monthly flow pattern. In this method, on average, 30.8% (range 18–48%) of the monthly flow allocated to the environmental flow, which is reasonable and acceptable amounts. Investigating the results of this study shows that the time pattern of the results should be analyzed in comparison with the observational flow pattern to estimate the environmental flow with a hydrological approach. The results also suggest that the methods that provide a constant amount of environmental flow in different months of the year should be interpreted cautiously along with other methods. [ABSTRACT FROM AUTHOR]

Seeking a process-based understanding for the shape of the flow duration curve (FDC) uniqueness to a catchment, this study applied a data-based rainfall-runoff modeling approach in perennial, intermittent and ephemeral catchments which would have different dominant rainfall-runoff processes. Using this approach, we identified (1) the number of dominant runoff processes in a catchment, (2) rainwater storage in all processes, (3) infiltrations and return flows between the processes. We then identified reasons for different FDC shapes in the catchments in terms of identified dominant processes. Our results showed a humid climate with lower aridity index (AI) would cause perennial flow created by the combination of four dominant processes of fast flow, faster and slower interflows and base flow components. On the contrary, an arid climate with higher AI would cause ephemeral flow created by the combination of two dominant processes of fast and faster interflow components. These indicate a FDC in arid catchments would become ephemeral because of less dominant runoff processes occurring only near ground surface, whereas a humid catchment would become perennial because of more dominant runoff processes occurring from near ground surface to deep underground. These findings contribute in estimating FDCs in ungauged catchments from climatic conditions. [ABSTRACT FROM AUTHOR]

Predicting the proportion of the water year a given stream will remain at or above various flow thresholds is critically important for making sound water management decisions. Flow duration curves (FDCs) succinctly capture this information using all data available over some historical period, while annual flow duration curves (AFDCs) instead use data from each individual water year. Analyzing the population of AFDCs, and in particular the tails of this distribution, can allow water managers to better prepare for years with extreme streamflow conditions. However, long time series of observations are necessary to capture interannual streamflow variations and are problematic to obtain in rapidly changing and poorly gauged catchments. By incorporating a process‐based model to construct AFDCs based on daily rainfall statistics and flow recession characteristics, the proposed approach is a first step toward addressing this challenge. Results indicate that prediction performance varies substantially across flow quantiles and that the current model fails to properly capture the interannual variability of low flows. Numerical analyses attributed these errors to nonlinearity in storage‐discharge relation, rather than cross‐scale streamflow correlations and non‐Poissonian rainfall, explaining the origin of commonly observed heavy‐tailed behavior in low flow quantiles. We present a case study on hydroelectric power generation, showing that faithfully capturing both interannual streamflow variability and recession nonlinearity has important implications for installation profitability. Key Points: Process‐based model of streamflow distribution distinguishes intraannual and interannual variabilityA nonlinear recession model improves performance; cross‐scale correlations and non‐Poissonian rainfall do notPredicting interannual variability of low flows improves infrastructure decisions [ABSTRACT FROM AUTHOR]

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Climate change is projected to affect the flow regime in urban waterways adversely. This study investigates the climate change impacts on the flow regime in the Lucas Creek catchment under three Representative Concentration Pathways (RCPs): RCP 2.6, RCP 4.5 and RCP 8.5. Flow Duration Curves (FDCs) and Indicators of Hydrological Alteration (IHA) methods are used to assess flow regime variations. Results of FDCs show a maximum rise of 370% in peak flow under RCP 4.5 however, low flow increases by 40%. Monthly streamflow increases up to 380% except for October and December. Similarly, the majority of the IHA parameters also show at least a 10% increase in their magnitudes under RCP 8.5. However, some parameters such as high pulse duration and rise rate decrease by 50% under RCP 4.5. The catchment would mainly suffer severe impact variations under RCP 4.5 and RCP 8.5 in the future. [ABSTRACT FROM AUTHOR]

Streamflow recession analysis characterizes the storage‐outflow relationship in catchments. This relationship, which typically follows a power law, summarizes all catchment‐scale subsurface hydrological processes and has long been known to be a key descriptor of the hydrologic response. In this paper, we tested a range of common recession analysis methods (RAMs) and propose the use of an analytic streamflow distribution model as an alternative method for recession parameter estimation and to objectively compare different RAMs. The used analytical model assumes power law recessions, in combination with a stochastic process for streamflow triggering rainfall events. This streamflow distribution model is used in the present framework to establish reference values for the recession parameters via maximum likelihood estimation. The model‐based method has two main advantages: (a) joint estimation of both power law recession parameters (coefficient and exponent), which are known to be strongly correlated, and (b) parameter estimation based on all available streamflow data (no recession selection). The approach is applied to five rainfall‐dominated catchments in Switzerland with 40 years of continuous streamflow observations. The results show that the estimated recession parameters are highly dependent on methodological choices and that some RAMs lead to biased estimates. The recession selection method is shown to be of prime importance for a reliable description of catchment‐scale recession behaviour, in particular in presence of short streamflow records. The newly proposed model‐based RAM yields robust results, which supports the further development of this method for comparative hydrology and opens new perspectives for understanding the recession behaviour of catchments. [ABSTRACT FROM AUTHOR]

ABSTRACT The main objective of the study was the evaluation of Characteristic Values and Exponential Curve methods as alternatives for flow permanence curves regionalization. Additionally, the use of regional flow indicators for the appropriation of reference flows associated with flow permanence curves was evaluated. The study area covered the Itapemirim and Itabapoana rivers watersheds, the most important located in the southern portion of the Espírito Santo state (Brazil). The Characteristic Values method presented best results in the flow permanence curves regionalization work. It was also concluded that the regional indicators represent a simple and consistent alternative for study area reference flows estimation.

Abstract Integrated hydrometeorological investigations are not frequently available at a regional scale over a longer time period, especially near the terminus of Indian Himalayan glaciers. An integrated approach to the collection of hydrological data has major advantages for understanding the runoff generation mechanisms at basin scale, particularly when coupled with meteorological observations. The current study involves time series analysis of hydrometeorological records collected near the terminus of the Chorabari Glacier, for four consecutive ablation seasons (June–Sept.) 2009–2012. The analysis shows that variation in rainfall was higher (c v = 0.9) at the same elevation over proximal sites, while the intensity of extreme rainfall events was 121–160 mm/d. The diurnal temperature range (DTR) has a tendency to reduce over the ablation season because of the onset of the Indian Summer Monsoon (ISM) and then further increases during the ISM withdrawal indicating humid-temperate conditions. The peak discharge (Q peak) was found to be higher during July and August. Snow and glacier melt contributed 76% of the total suspended sediment transport during peak ISM months (July and August) reflecting seasonal evolution of the hydrologic conduits. The results indicate that Karakoram and western Himalayan glaciers produce comparatively low sediment yield compared to central Himalayan glaciers. The hydrological variations are depicted through flow duration curves (FDC) for meltwater discharge and sediment load. The flow corresponding to Q 50 , Q 75 , and Q 90 (where Q x is the discharge that is exceeded x percent of the time referred to as % dependability) are 4.2, 3.7, and 2.8 m3/s; and the corresponding dependability for suspended sediment loads (SSLs) are 409.0, 266.0, and 157.2 t/d, respectively. The daily SSL and discharge (Q) from 2009 to 2012 were used to develop a sediment rating curve (SSL = 39.55 × Q1.588, R2 = 0.8). Multiple regressions are used to determine the impacts of meteorological parameters on glacier melt. The meteorological conditions, hydrological characteristics, and suspended sediment delivery for the Chorabari Glacier provide insight on meltwater generation processes and sediment transport patterns during the ISM season. Highlights • High paucity in hydrometeorological records at higher elevations above 2000 m in the Indian Himalayan region. • Rainfall and temperature are dominant meteorological factors controlling melting processes and sediment delivery patterns. • Himalayan glaciers generate very high sediment yield during peak monsoon months (July and August). • Hydrometeorological records should be standardized for the glaciers of the Indian Himalayan region. [ABSTRACT FROM AUTHOR]

Abstract The Mana Pools flood plain along the Middle Zambezi River and part of the popular Mana Pools National Park of Zimbabwe has been experiencing both ecological and morphological changes since the construction of upstream hydropower reservoirs. This study investigated the hydro-dynamics from natural and human influenced flows, particularly at the Mana Pools floodplains which are downstream of Kariba and Kafue hydropower dams. Descriptive statistics were used to analyse the differences in flow regime upstream and downstream of the hydropower reservoirs. A standard t -test was done to compare the natural and modified mean annual flows. Results show that the presence of upstream reservoirs has reduced the high peak average monthly flows by 17% and increased the average monthly low flows by 5% at Mana Pools. However, the mean annual runoff has not significantly changed. Results also established that. In line with recent calls for ecological considerations in reservoir management, the study recommends that the reservoir operation in the Middle Zambezi River should mimic the pre-impoundment Middle Zambezi River flow regime at Mana Pools. Highlights • Hydro-dynamics from natural and human influenced flows at Mana Pools floodplains investigated. • Flow duration curves, statistics and tracing contours from water levels used. • Upstream reservoirs reduced the peak and low average monthly flows by 17% and 5% respectively. • Effects observed at monthly level have not significantly affected the mean annual runoff. • Mana Pools catchment contributes 7.2% of the total flows at Mana Pools. [ABSTRACT FROM AUTHOR]

Streamflow records play important role for design, planning and management of water structures in any region. In order to use the streamflow efficiently for these purposes, the length of data records must be statistically sufficient and complete. But, there are usually some gaps at the streamflow records and these gaps must be infilled by means of reliable methods. In this study, the missing streamflow records in the gauge stations 2119, 2151, 2149, 2158 and 2122, which are located in the upper and middle parts of the Euphrates Basin, were estimated using Flow Duration Curves and Regression Models. To define the best model among alternatives, determination coefficient (R2) and Root Mean Square Error (RMSE) were used. According to the results, both of the models produced successful results with a high value of R2. Moreover, the results showed that the Regression Models for the stations 2151, 2119, 2122 and 2158 and Flow Duration Curves for the station 2149 were more capable to preserve the main statistical properties of the historical data. [ABSTRACT FROM AUTHOR]

Runoff variability is investigated separately for the Wei, the Bei, and the Qing Rivers in China with a focus on their respective differences in monthly flow patterns and flow duration curves (FDCs) between years with and without annual runoff deficit. The number of deficit runoff years increased in the Wei River and changed slightly in the Bei and Qing Rivers, respectively. Monthly flow variation patterns and FDCs differ between deficit and non-deficit years. The deficit years generally demonstrate earlier and more dispersed flow maxima. Deficit runoff years are contingent with the negative phase of the Polar-Eurasian Oscillation and vice versa, while generally they show contingency with the positive phase of the SST (Niño 3.4) and vice versa. The correlation between the human activity factors and the weights obtained by decomposing the runoff series into empirical orthogonal functions indicated that the human impact on the runoff variation was detectable: 22-25% in the Wei River, 28% in the Bei River, and negligible in the Qing River. We projected FDCs by weighting the distinctly different FDCs for deficit/non-deficit years according to several precipitation scenarios. [ABSTRACT FROM AUTHOR]

Future streamflow patterns of three subbasins, i.e., East Holland, Beaver, and Pefferlaw River basins, located in the upstream of Lake Simcoe of Canada are assessed for 2021–2099. The individual set of parameters of a conceptual hydrological model, HBV (Hydrologiska Byråns Vattenbalansavdelning)-light, are first calibrated for these three subbasins. The calibrated model was validated and further used to estimate the future stream flow driven by statistically down scaled projected precipitation and air temperature from the Pacific Climate Impacts Consortium under Representative Concentration Pathways 8.5 and 4.5 scenarios. The uncertainty of annual stream flow, hydro graph, flow duration curve (FDC), and flood frequency were evaluated. The results reveal that the annual streamflows of the Beaver and Pefferlaw River Basins (PRB) are projected to slightly increase in 2020–2099 while the annual stream flows of the East Holland River Basin (EHRB) are expected to be similar in 2020–2099. The monthly streamflow in winter is projected to increase but to decrease in spring across three subbasins. Based on the projected FDCs, daily stream flow of EHRB and PRB will likely increase by 2070–2099. [ABSTRACT FROM AUTHOR]

This paper presents a novel method to estimate flow duration curves (FDCs) for ungauged catchments with permanent flow. It is based on a dataset of 521 catchments located throughout France. The method consists in a three-step procedure called the Quantile Solidarity (QS) approach. First, a regression-based model is built to estimate FDCs in ungauged catchments, linking each flow quantile independently to physical descriptors. The second step involves imposing the continuity of the regression-based model parameters along the quantiles (hence quantile solidarity) to obtain a large reduction in the number of parameters used to estimate the FDC. The last step consists in spatially interpolating the model residuals to further improve the performance of the FDC estimation. The QS approach yields a robust and parsimonious FDC estimation without any loss in simulation efficiency and ensures strictly monotonic FDCs. [ABSTRACT FROM AUTHOR]

This study presents novel models for prediction of flow Duration Curves (FDCs) at ungauged basins using artificial neural networks (ANN) and Gene Expression Programming (GEP) trained and tested using historical flow records from 171 unregulated and 89 regulated basins across North America. For the 89 regulated basins, FDCs were generated for both before and after flow regulation. Topographic, climatic, and land use characteristics are used to develop relationships between these basin characteristics and FDC statistical distribution parameters: mean ( m ) and variance ( ν ). The two main hypotheses that flow regulation has negligible effect on the mean ( m ) while it the variance ( ν ) were confirmed. The novel GEP model that predicts the mean (GEP- m ) performed very well with high R 2 (0.9) and D (0.95) values and low RAE value of 0.25. The simple regression model that predicts the variance (REG- v ) was developed as a function of the mean ( m ) and a flow regulation index (R). The measured performance and uncertainty analysis indicated that the ANN -m was the best performing model with R 2 (0.97), RAE (0.21), D (0.93) and the lowest 95% confidence prediction error interval (+0.22 to +3.49). Both GEP and ANN models were most sensitive to drainage area followed by mean annual precipitation, apportionment entropy disorder index, and shape factor. [ABSTRACT FROM AUTHOR]

Prediction of natural streamflow in regulated rivers for derivation of ecologically relevant streamflow metrics (ERSFMs) and prediction in ungauged basins (PUB) are important in management of water resources. However, specific studies on comparison of methods for predicting hourly flow regime relevant to ecological study in regulated (hydropeaking) rivers are rare in literature. Therefore, using catchments in mid Norway, we performed comparative evaluation of prediction of hourly streamflow series and flow duration curves (FDCs) in ungauged basins. We developed a regional regression model based on relationships among streamflow percentiles and drainage areas and performed a regional calibration of a streamflow recession based precipitation-runoff (P-R) model. A leave one out cross-validation procedure was used to evaluate the regional models. The results indicate that the regional regression model with transferring of streamflow information based on the nearest neighbour performed better than both transferring optimal parameters from local calibration and regional parameter sets corresponding to maximum regional weighted average Nash-Sutcliffe efficiency of the P-R model (NSEMRWA). We also evaluated the models based on prediction of some environmental indices: the daily range, daily standard deviation, flashiness, maximum ramping rate, number of rise and falls and daily flow changes. However, both modelling strategies predicted hourly streamflow indices well and appeared stable over most indices while the largest differences occurred in the rise and fall counts. The models were further applied for prediction of the natural streamflow time series at Sokna hydropeaking plant. The observed hydrograph exhibits continuous sudden fluctuations while the predicted natural flow hydrograph exhibits smooth pattern. The within a year FDCs for observed flow exhibits sharp transitions from high to low flows. There is clear differences between the environmental indices obtained for the observed and the modelled data series, with the general observation that the NSEMRWA computing a smaller variability than the regression model. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The issue of lack of donor basins for prediction of flow duration curves (FDCs) in ungauged basins (PUB) is an important area of research that is not resolved in the literature. We present a distance based approach to predict FDCs at ungauged basins by quantifying the dissimilarity between FDCs and characteristics data of basins. This enables us to bracket hydrologically similar basins and thus allowing us to estimate FDCs at ungauged basins. Generally, a single regression model is selected to make hydrological estimates at an ungauged basin. Based on established laws and theories of hydrology, we work to devise a method to improve the output of selected model for an ungauged basin by swapping it with another model in case the latter gives better coverage and statistical estimates of the nearest neighbors of an ungauged basin. We report two examples to demonstrate the effectiveness of model swapping. Out of 124 basins used in analysis, 34 basins in example 1 and 41 basins in example 2 fulfill the set criteria of model swapping and subsequently their estimates are improved significantly. [ABSTRACT FROM AUTHOR]

In this study, the potential impacts of road topography on hydrologic responses at the watershed scale were simulated. The method considered used a geographic information system to identify road embankment locations and subsequently remove them from the baseline elevation data. Starting from both the 'with' and 'without' road elevation model, the surface and near-surface hydrological responses for 20 watersheds in Sweden were modeled in HEC-HMS under three different storm intensities. Flow duration curves (FDCs) were used to compare hydrologic responses for the different modeling scenarios under the various storm intensities. Specifically, L-moment ratios of the FDCs were calculated and their variation compared. Results showed an increase in peak flow amounts and reduction in time to peak with increased storm intensity. In addition, variations of the L-moment ratios were larger in larger watersheds. However, the impact of the roads on the modeled hydrologic responses was much smaller than anticipated and only identifiable through detailed examination of the L-moment statistical descriptors. Our findings not only highlight the potential impacts of road topography on watershed-scale hydrology (especially concerning high intensity storms) but also provide a methodology for detecting the even rather small changes that could manifest, for example, under coupled road network and climatic changes. [ABSTRACT FROM AUTHOR]

The aim of this study is to determine the hydro-power potentials of selected rivers in Edo State using hydrological indices. Four Rivers were investigated namely Ovia, Ikpoba Edion, Orlie Rivers. Discharge measurement was carried out for 12 calendar months, from January 2013 to December 2013 using the grid point technique, commonly known as velocity-area method while Gross Hydropower Potential GHP was determined using model developed by UNIDO. Highest monthly hydropower yields were recorded in September for Ovia, Ikpoba and Edion Rivers and in August for Orlie River. On annual basis, Ovia River, recorded the highest power yield of 61.619MW (suggesting that Ovia river may be suitable for a Medium hydropower scheme, 10MW-100MW) with the highest monthly power yield of 42.381MW recorded in September, followed by August (7.047MW). Lowest power yield of 0.019MW was recorded in February. In Ikpoba River, annual hydropower yield was recorded as 14.78MW, while the lowest power yield of 0.02MW was recorded in April. Highest yield of 5.76MW was recorded in september. River Orlie recorded an annual hydropower yield of 9.819 MW, with August having the highest power yield of 3.296MW. Other significant hydropower yield values were recorded in September and July. Edion River has an annual power yield of 5.49MW. Lowest yield in this river was recorded in April. The dependability of flow for hydropower operations were evaluated using the Flow Duration Curve (FDC). The results showed that extreme high monthly discharge volumes of 544.8m³in Ovia river, 172m³ in Ikpoba river, 102.1m³ in Orlie and 57.1m³ in Edion have dependability percentages of less than 10%. Notwithstanding the hydrological conditions of these rivers can be categorized as adequate (15%-40%) to average moisture conditions (40%-60%). [ABSTRACT FROM AUTHOR]

Summary Hydrologic systems can be altered by anthropogenic and climatic influences. While there are a number of statistical frameworks for describing and evaluating the extent of hydrologic alteration, here we present a new framework for assessing whether statistically significant hydrologic alteration has occurred, or whether the shift in the hydrologic regime is consistent with the natural variability of the system. Four hypothesis tests based on shifts of flow duration curves (FDCs) are developed and tested using three different experimental designs based on different strategies for resampling of annual FDCs. The four hypothesis tests examined are the Kolmogorov–Smirnov (KS), Kuiper ( K ), confidence interval (CI), and ecosurplus and ecodeficit (Eco). Here 117 streamflow sites that have potentially undergone hydrologic alteration due to reservoir construction are examined. 20 years of pre-reservoir record is used to develop the critical value of the test statistic for type I errors of 5% and 10%, while 10 years of post-alteration record is used to examine the power of each test. The best experimental design, based on calculating the mean annual FDC from an exhaustive jackknife resampling regime, provided a larger number of unique values of each test statistic and properly reproduced type I errors. Of the four tests, the CI test consistently had the highest power, while the K test had the second highest power; KS and Eco always had the lowest power. The power of the CI test appeared related to the storage ratio of the reservoir, a rough measure of the hydrologic alteration of the system. [ABSTRACT FROM AUTHOR]

The three-parameter Burr XII distribution has been seldom used in hydrological applications, although it is particularly appealing because its range covers positive values only, which is convenient when modeling streamflows or rainfall data. Moreover, it has two shape parameters, allowing it to be quite adaptable to different samples because it covers a wide range of skewness and kurtosis values. Parameter estimation methods currently available in the literature require the numerical solution of two joint nonlinear equations to estimate the shape parameters of the distribution. This work proposes a simplified, although accurate, method to analytically compute the two shape parameters starting from the dimensionless L-moments ratios representing the distribution's variability (L-CV) and skewness (L-skewness). The obtained parameters can be directly used in practical applications or otherwise may be useful to properly initialize the algorithms to obtain a numerical solution for the shape parameters. A detailed analysis of the accuracy of the approximated solution is performed, showing that the errors in the estimation of the distribution quantiles are negligible compared with the sample variability typically affecting hydrological samples. An extensive data set of empirical flow duration curves from stations located in northwestern Italy is considered to demonstrate the suitability of the extended Burr XII distribution to represent flow duration curves in a wide range of situations. [ABSTRACT FROM AUTHOR]

Streamflow can be drastically perturbed in urban basins with important implications for stream, floodplain, and riparian ecosystems. Normally, the dynamic influence of urbanization on streamflow is studied via space-for-time substitution. Here we explicitly consider urban growth when determining the flow regime of 14 urban basins. To synthetically represent the flow regime, we employ flow duration curves (FDCs) determined using a stochastic model. The model permits derivation of FDCs that are dependent on few parameters representing climatic, land use, conventional stormwater management, and geomorphological conditions in an urban basin. We use the model, under conditions of urban growth, to assess the influence of urbanization on key model parameters and to determine different indicators of hydrologic alteration. Overall, results indicate consistent changes in the temporal evolution of the perturbed flow regimes, which in this case can largely be explained by the progressive redistribution with urban growth of water from slow subsurface runoff and evapotranspiration to fast urban runoff. [ABSTRACT FROM AUTHOR]

To better understand the driving forces of changes in streamflow ( Q), this study analyzed the changes in the hydro-meteorological series by the Mann-Kendall, Pettitt's test and the flow duration curve (FDC) in the Wuding River Basin (WRB), which is a typical river basin in the Loess Plateau. The response of Q variability to climate change and human activities were also quantified by the elasticity method and decomposition method based on the Budyko framework. The results showed that Q exhibited an obvious downward trend at the rate of 0.44 mm/y with a changing point occurred in 1980. Compared with 1961-1980, the greatest reduction in monthly Q during 1981-2007 was found in April (41 %) and the low flows have more distinct decrease than high flows. The precipitation ( P), potential evapotranspiration ( E) and catchment characteristics parameter n elasticity of Q are 2.40, −1.40 and −2.51, respectively, indicating that Q variability is most sensitive to human activities. The contribution of climate change and human activities to changes in Q from the two methods are 35 and 65 %, respectively. The ecological restoration (ER) measures, including channel measures and slope measures, were found to be the dominant factors responsible for the decreased Q. Furthermore, changes in Q in 1970-1990 could be mainly ascribed to channel measures while slope measures have played more important roles after 1999 when the Grain-for-Green (GFG) project was implemented. This study could provide scientific basis for how to mitigate effectively and efficiently changes in water resources and guide measures to be implemented in the region under the future climate change. [ABSTRACT FROM AUTHOR]

Bedload yields were calculated by 39 methods at the East Tributary gauge, nine methods at Upper Swift Creek gauge and 11 methods at Swift Creek gauge in the Ngarradj Creek catchment in northern Australia. These methods involved combining various significant bedload rating curves determined for a measured bedload data set for a 4-year period with either the hourly or daily hydrographs or flow duration curves for the same period, 1 September 1998 to 31 August 2002. Bedload ratings were both statistically significant ( ρ ≤ 0.05) and explained at least 60% of the variance in bedload flux. Bias corrections were used with all methods based on log10-transformed ratings. Estimated mean annual bedload yields varied by three orders of magnitude at the East Tributary gauge and by two orders of magnitude at Upper Swift Creek and Swift Creek gauges. Hourly discharges usually produced higher estimated yields than daily discharges. The bedload rating-flow duration curve technique overestimates yields and bias correction methods always produce even higher yields. Ratings using both immersed bedload weight and adjusted immersed bedload weight always under-predicted yields because they contain an implicit threshold of motion condition that is at least four times greater than that predicted by Bagnold's threshold equation. Such a result questions the applicability of Bagnold's threshold equation to the Ngarradj Creek catchment. The best estimates of mean annual bedload yield at East Tributary, Upper Swift Creek and Swift Creek gauges are 600 ± 170 (SE), 1065 ± 150 and 1795 ± 270 t/year, respectively. © 2015 Commonwealth of Australia. Hydrological Processes © 2015 John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Few studies have examined how insect outbreaks affect landscape-level hydrologic processes. We report the hydrologic effects of the invasive, exotic hemlock woolly adelgid (HWA) in a headwater catchment in the southern Appalachian Mountains. The study watershed experienced complete mortality of an evergreen tree species, Tsuga canadensis (L.) Carr. (eastern hemlock), after infestation was first detected in 2003. Hemlock mortality resulted in a ~6% reduction in basal area in the watershed, and this loss was primarily concentrated in riparian zones. We used a paired-watershed approach to quantify changes in water yield and peak stormflow using streamflow data from the infested watershed and a nearby watershed with significantly lower hemlock basal area. We hypothesized that yieldwould increase shortly after hemlock infestation but decrease over the longer-term. Wefound that annual yield did not increase significantly in any year after infestation but decreased significantly by 12·0cm (~8%) in 2010. Monthly yield also decreased after infestation, but changes were limited to the dormant season. The decline in yield is likely to persist as hemlock is replaced by species with higher transpiration rates. Peakflow increased significantly after infestation during the two largest flow events in the post-infestation period. Changes in stormflow during extreme events may have been temporary as another evergreen, Rhododendron maximum, may have mitigated some of the changes after hemlock loss. Thus, streams draining watersheds where eastern hemlock has been lost due to HWA infestation demonstrate permanent reductions in yield and transient increases in peakflow during large-flow events. Published 2014. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

There is growing evidence that changes in the current hydrological behaviour of urbanising catchments are a major source of impacts on the downstream water bodies. However, current flow-rates are rarely considered in studies on urban stormwater management, usually focused on extreme flow-rates. We argue that taking into account receiving water bodies is possible with relatively small modifications in current practices of urban stormwater modelling, through the use of Flow duration curves (FDCs). In this paper, we discuss advantages and requirements of the use of FDCs. Then, we present an example of application comparing source control regulations over an urbanised catchment (178 ha) in Nantes, France. [ABSTRACT FROM AUTHOR]