We propose a convenient procedure for the matching strip method in determining the recession constant of the master recession curve using the ratio of flow over successive days (Q
n+1
/Q
n
). The ...method is applied to 29 basins (6.1-740 km
2
) in eastern Japan to develop linear regression models that estimate low flow indices through the recession constant (λ), and either mean annual precipitation or mean annual runoff. Significant models were developed for Q7
10
(seven-day 10-year low flow), and Q97
10
(10-year low flow exceeded 97% of the time) in the case of all basins, and in particular for basins classified into sedimentary or igneous geology (adjusted R
2
up to 0.784). When basins were not classified by geology, models based on mean annual runoff as the second independent variable performed better than those based on mean annual precipitation, with adjusted R
2
values of 0.705 and 0.717 for the Q7
10
and Q97
10
models, respectively.
Much has been written on the subject of objective functions to calibrate rainfall-runoff models. Many studies focus on the best choice for low-flow simulations or different multi-objective purposes. ...Only a few studies, however, investigate objective functions to optimize the simulations of low-flow indices that are important for water management. Here, we test different objective functions, from single objective functions with different discharge transformations or using low-flow indices, to combinations of single objective functions, and we evaluate their robustness and sensitivity to the rainfall-runoff model. We find that the Kling and Gupta efficiency (KGE) applied to a transformation of discharge is inadequate to fulfil all assessment criteria, whereas the mean of the KGE applied to the discharge and the KGE applied to the inverse of the discharge is sufficient. The robustness depends on the climate variability rather than the objective function and the results are insensitive to the model.
EDITOR A. Castellarin; ASSOCIATE EDITOR C. Perrin
Rising temperatures and changes in precipitation patterns in the last decades have led to an increased awareness on low flow and droughts even in temperate climate zones. The scientific community ...often considers low flow as a consequence of drought. However, when observing low flow, catchment processes play an important role alongside precipitation shortages. Therefore, it is crucial to not neglect the role of catchment characteristics. This paper seeks to investigate low flow and drought in an integrative catchment approach by observing the historical development of low flows and drought in a typical German low mountain range basin in the federal state of Hesse for the period 1980 to 2018. A trend analysis of drought and low flow indices was conducted and the results were analyzed with respect to the characteristics of the Gersprenz catchment and its subbasin, the Fischbach. It was shown that catchments comprising characteristics that are likely to evoke low flow are probably more likely to experience short-term, seasonal low flow events, while catchments incorporating characteristics that are more robust towards fluctuations of water availability will show long-term sensitivities towards meteorological trends. This study emphasizes the importance of small-scale effects when dealing with low flow events.
•Effects of forest plantation cover on water available to downstream users are examined.•Forest cover flow change model is used to simulate forest plantation effects on streamflow.•Forest management ...strategies as forest cover proportion should be adopted to reduce fast-growing forest effects on streamflow.•Low flow indices (7Q10 and Q90) could be used to examine the thresholds effects of forest plantation.•Planning forest plantation area could contribute to hydrosolidarity concept.
São Paulo State, Brazil.
This study assessed the influence of forest plantations on streamflow in a gauged catchment (85 ha), covered with fast-growing Eucalyptus sp. plantations. One strategy for reducing the effects of plantations on streamflow is to reduce the area of a catchment occupied by forest, and in this context, our objectives were to simulate the effects on streamflow of different proportions of forest cover (70%, 50% and 0% of the forest cover). Moreover, we used low-flow indices (Q90 and 7Q10) to examine the effects of such scenarios on water availability for downstream users.
Fast-growing forest plantation areas have been expanding globally, with simultaneously increasing concerns about the water consumption of these forests, especially in water-limited regions with consequences for downstream users. Simulations of scenarios with varying forest cover proportions showed an annual streamflow increase of 90% when clear-cutting had removed the forest cover in the catchment. The 100% forest cover scenario produced rates of streamflow below the low flow indices, resulting in less water availability for downstream water users. The reduction in forest cover proportion at the catchment scale promoted an attenuation of water use. Therefore, forest plantation management should adopt management strategies such as regulating the forest cover proportion to minimize the effects on water supply for downstream water users.
At the beginning of the 21st century, ongoing climate change led to research into extreme streamflow phenomena. This study aimed to assess the patterns of low-flow changes in different hydrological ...regions of Lithuania using selected hydrological indices (the annual minimum 30-day flow (m3 s−1) of the warm period—30Q), its duration, and deficit volume (below the 80th and 95th percentile flow: 30Q80 and 30Q95). Differences in low-flow indices in separate hydrological regions and over different periods (1961–2020, 1961–1990, 1991–2020) were analyzed, applying the HydroOffice tool, the TREND software package, and mapping using the Kriging interpolation. The highest specific indices of 30Q were estimated in the Southeastern hydrological region (3.97 L/s·km2) and the lowest in the Central hydrological region (1.47 L/s·km2). In general, the 30Q values in the periods 1961–2020 and 1991–2020 had no trends. In 1961–1990, trends in 30Q data were significantly positive, and positive in most investigated rivers of the Western and Central hydrological regions. The average number of dry days at both thresholds decreased in the Western and Southeastern hydrological regions and increased in the Central hydrological region comparing two subperiods.
•The paper presents a regional investigation of flow duration curves.•The investigated region is mainly characterized by an highly fractured geological area and by a Mediterranean climate.•Flow ...duration curve shape is mainly affected by hydro-geological settings.
The flow duration curve (FDC) can provide information about the integral catchment response to rainfall events that span from low volume events to events of flood magnitude, and the FDC is particularly useful for low flow regime characterization. The focus of this study was to introduce a statistical, parsimonious approach with a conceptually based parameterization that can lead to simple and practical tools for FDC predictions that can be applied to contexts, such as the Mediterranean climate, that involve scarce data and regional geological and hydro-geological features that strongly affect low-flow hydrological regimes. At-site, dimensionless, empirical FDCs were represented with three-parameter log normal distributions, the variations in the corresponding parameters versus the base flow index (BFI) were explored, and the conceptual relationship of these parameters is further discussed. In cases of ungauged catchments for which the BFI is not known, a priori estimates of such indices can be derived from permeability indices, as BFIs are strongly related to permeability indices in the studied region (Longobardi and Villani, 2008). For moderate to large permeability catchments, which represent the largest fraction of the investigated catchments, prediction errors associated with the proposed regional method of FDC assessment, which is particularly suited for regions for which only scarce or poor data are available, averaged approximately 18%.
Low flow is one of the very effectual hydrologic parameters on the state of aquatic ecosystems as well as power production, reservoir management and industry. Therefore, it is necessary to ...investigate the changes in this parameter in the future periods under affecting factors such as climate change. In this regard, the impacts of climate change on low flows of Sepid dasht sezar catchment were evaluated, in this research. First, the ability of IHACRES rainfall-runoff model for simulation of low flows of this catchment was evaluated. After calibration and verification of model, in this study observed that the model has a good ability for simulating of mean daily flow (R2-log>0.7), also low flow (R2-inv>0.6). In addition, the ability of model to low flow indices (including Q95, AM7Q with different return period and QdefS)was evaluated. Then, The outputs of the temperature and precipitation of 10 general circulation models of the atmosphere under A2 emission scenario was used in order to assess the effects of climate change over the period 2015-2044. LARS-WG model was applied for downscaling of the output of these 10 models. Finally, downscaled values of temperature and precipitation were introduced to the IHACRES rainfall - runoff model and the low flow in the future was assessed based on the low flow indices. Changes of two indices Q95 and AM7Q in the future period to the past, based on the median of 10 AOGCM model results is decreasing (-40% for Q95 and from -52% to -79% for AM7Q with different return period). Also, the QdefS index show the increasing change (30% based on the median of AOGCM model results). All three indices have confirmed each other's results and show that the expected climate change in the future, greatly affect the low flows.
L'estimation d'indices d'étiage est d'une grande importance pour une meilleure connaissance de la ressource en eau disponible et en déduire des règles de gestion de cette ressource et des risques ...associés. Idéalement, ces indices sont calculés en sites jaugés à partir de longues chroniques de débits mesurés. En sites non jaugés, ces indices doivent être estimés. Cette thèse s'inscrit dans le projet d'amélioration de l'outil informatique " LoiEau " utilisé par les DREAL et les Agences de l'eau. Le principal objectif est de développer un modèle hydrologique simple et flexible pour estimer tous les indices d'étiage souhaités à des intervalles de temps journaliers ou supérieurs en sites non jaugés. La simplicité du modèle repose sur l'hypothèse forte que deux paramètres plus facilement régionalisables suffisent à estimer les indices avec une précision voulue. Cette précision dépend de la fonction objectif qu'il a fallu adapter aux faibles débits pour caler convenablement les paramètres du modèle sur des sites jaugés. Le modèle se veut flexible dans le sens où il est applicable à une large variété de bassins versants. Il a été comparé au modèle journalier à quatre paramètres GR4J et au modèle mensuel à deux paramètres LoiEau en s'intéressant aussi à la façon de régionaliser les paramètres. Des comparaisons ont également été réalisées avec une méthode d'estimation dite stochastique d'un indice d'étiage classique. Ces travaux montrent le potentiel du modèle à deux paramètres et l'avantage du pas de temps journalier, la variabilité temporelle des précipitations n'étant pas sans conséquence sur l'estimation de débits moyens en raison de la non-linéarité des modèles pluies-débits.
Estimating low-flow indices is of paramount importance to understand low flows and to manage water resources and risk assessments. These indices are derived from time-series of river discharges that are measured at gauged sites over long periods. At ungauged sites, the indices must be estimated. This research work is part of a project to improve “LoiEau”, a software package that is used by French regional environmental or water agencies. The main objective is to develop a simple and flexible rainfall-runoff model to simulate low-flow indices of ungauged sites at daily or longer time intervals. The model simplicity relies on the strong assumption that two free parameters are sufficient to provide accurate enough estimates of low-flow indices, yet making easier the regionalisation of models. The model accuracy depends on the objective function that is used to calibrate model parameters on gauged sites and had to be adapted to low-flow simulations. The model is flexible in the sense that it is designed to fit to a wide variety of catchments and hydro-meteorological behaviours. This model was compared with GR4J, a daily rainfall-runoff model which involves four parameters, and LoiEau, a monthly model. Comparisons were also carried out with a stochastic estimation method applied to a specific low-flow index. This research work shows the potential of the two-parameter model, but also the advantage of a daily time step to account for the temporal variability of precipitations, which is not without consequence on the assessment of average discharges due to the nonlinearity of rainfall-runoff models.
Low flow indices are of interest for a number of water‐related applications. Conventionally, low flow indices are derived from continuous streamflow data; however, these data may not always be ...available for analysis. A number of techniques have therefore been developed for low flow estimation in ungauged catchments. These approaches vary in complexity and in the amount of initial data required to generate the low flow model. In the UK, software is available which assists in low flow estimation for ungauged catchments. However, certain desktop studies only require a simple evaluation of low flows, with specific low flow indices, such as the Q95 index, being of interest. In this case, the use of such software may not be justified or required in the first instance. This paper demonstrates that a simple regression model is adequate for low flow estimation for multisite analysis where the order magnitude of the low flow index is of importance.
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