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  • 51.
    Sikorska, A. E.
    et al.
    Univ Zurich, Dept Geog, Zürich.; Warsaw Univ Life Sci SGGW, Dept Hydraul Engn, Warsaw.
    Seibert, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Univ Zurich, Dept Geog, Zürich, Switzerland.
    Value of different precipitation data for flood prediction in an alpine catchment: A Bayesian approach2018In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 556, p. 961-971Article in journal (Refereed)
    Abstract [en]

    Flooding induced by heavy precipitation is one of the most severe natural hazards in alpine catchments. To accurately predict such events, accurate and representative precipitation data are required. Estimating catchment precipitation is, however, difficult due to its high spatial, and, in the mountains, elevation-dependent variability. These inaccuracies, together with runoff model limitations, translate into uncertainty in runoff estimates. Thus, in this study, we investigate the value of three precipitation datasets, commonly used in hydrological studies, i.e., station network precipitation (SNP), interpolated grid precipitation (IGP) and radar-based precipitation (RBP), for flood predictions in an alpine catchment. To quantify their effects on runoff simulations, we perform a Bayesian uncertainty analysis with an improved description of model systematic errors. By using periods of different lengths for model calibration, we explore the information content of these three datasets for runoff predictions. Our results from an alpine catchment showed that using SNP resulted in the largest predictive uncertainty and the lowest model performance evaluated by the Nash–Sutcliffe efficiency. This performance improved from 0.674 to 0.774 with IGP, and to 0.829 with RBP. The latter two datasets were also much more informative than SNP, as half as many calibration data points were required to obtain a good model performance. Thus, our results show that the various types of precipitation data differ in their value for flood predictions in an alpine catchment and indicate RBP as the most useful dataset.

  • 52.
    Sikorska, A. E.
    et al.
    Univ Zurich, Dept Geog, Zürich.; Warsaw Univ Life Sci SGGW, Dept Hydraul Engn, Warsaw.
    Viviroli, D.
    Univ Zurich, Dept Geog, Zürich.
    Seibert, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Univ Zurich, Dept Geog, Zürich.
    Effective precipitation duration for runoff peaks based on catchment modelling2018In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 556, p. 510-522Article in journal (Refereed)
    Abstract [en]

    Despite precipitation intensities may greatly vary during one flood event, detailed information about these intensities may not be required to accurately simulate floods with a hydrological model which rather reacts to cumulative precipitation sums. This raises two questions: to which extent is it important to preserve sub-daily precipitation intensities and how long does it effectively rain from the hydrological point of view? Both questions might seem straightforward to answer with a direct analysis of past precipitation events but require some arbitrary choices regarding the length of a precipitation event. To avoid these arbitrary decisions, here we present an alternative approach to characterize the effective length of precipitation event which is based on runoff simulations with respect to large floods. More precisely, we quantify the fraction of a day over which the daily precipitation has to be distributed to faithfully reproduce the large annual and seasonal floods which were generated by the hourly precipitation rate time series. New precipitation time series were generated by first aggregating the hourly observed data into daily totals and then evenly distributing them over sub-daily periods (n hours). These simulated time series were used as input to a hydrological bucket-type model and the resulting runoff flood peaks were compared to those obtained when using the original precipitation time series. We define then the effective daily precipitation duration as the number of hours n, for which the largest peaks are simulated best. For nine mesoscale Swiss catchments this effective daily precipitation duration was about half a day, which indicates that detailed information on precipitation intensities is not necessarily required to accurately estimate peaks of the largest annual and seasonal floods. These findings support the use of simple disaggregation approaches to make usage of past daily precipitation observations or daily precipitation simulations (e.g. from climate models) for hydrological modeling at an hourly time step.

  • 53. Staudinger, Maria
    et al.
    Seibert, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Predictability of low flow - An assessment with simulation experiments2014In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 519, no Part B, p. 1383-1393Article in journal (Refereed)
    Abstract [en]

    Summary Since the extreme summer of 2003 the importance of early drought warning has become increasingly recognized even in water-rich countries such as Switzerland. Spring 2011 illustrated drought conditions in Switzerland again, which are expected to become more frequent in the future. Two fundamental questions related to drought early warning are: (1) How long before a hydrological drought occurs can it be predicted? (2) How long are initial conditions important for streamflow simulations? To address these questions, we assessed the relative importance of the current hydrological state and weather during the prediction period. Ensemble streamflow prediction (ESP) and reverse ESP ( ESP rev ) experiments were performed with the conceptual catchment model, HBV, for 21 Swiss catchments. The relative importance of the initial hydrological state and weather during the prediction period was evaluated by comparing the simulations of both experiments to a common reference simulation. To further distinguish between effects of weather and catchment properties, a catchment relaxation time was calculated using temporally constant average meteorological input. The relative importance of the initial conditions varied with the start of the simulation. The maximum detectable influences of initial conditions ranged from 50 days to at least a year. Drier initial conditions of soil moisture and groundwater as well as more initial snow resulted in longer influences of initial conditions. The catchment relaxation varied seasonally for higher elevation catchments, but remained constant for lower catchments, which indicates the importance of snow for streamflow predictability. Longer persistence seemed to also stem from larger groundwater storages in mountainous catchments, which may motivate a reconsideration of the sensitivity of these catchments to low flows in a changing climate.

  • 54.
    Sterte, Elin Jutebring
    et al.
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, Umeå, Sweden; DHI Sweden AB, Stockholm, Sweden.
    Johansson, Emma
    Swedish Nucl Fuel & Waste Management Co, Solna, Sweden.
    Sjoberg, Ylva
    Stockholm Univ, Dept Phys Geog, Stockholm, Sweden; Stockholm Univ, Bolin Ctr Climate Res, Stockholm, Sweden.
    Karlsen, Reinert Huseby
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Laudon, Hjalmar
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, Umeå, Sweden.
    Groundwater-surface water interactions across scales in a boreal landscape investigated using a numerical modelling approach2018In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 560, p. 184-201Article in journal (Refereed)
    Abstract [en]

    Groundwater and surface-water interactions are regulated by catchment characteristics and complex inter- and intra-annual variations in climatic conditions that are not yet fully understood. Our objective was to investigate the influence of catchment characteristics and freeze-thaw processes on surface and groundwater interactions in a boreal landscape, the Krycklan catchment in Sweden. We used a numerical modelling approach and sub-catchment evaluation method to identify and evaluate fundamental catchment characteristics and processes. The model reproduced observed stream discharge patterns of the 14 sub-catchments and the dynamics of the 15 groundwater wells with an average accumulated discharge error of 1% (15% standard deviation) and an average groundwater-level mean error of 0.1 m (0.23 m standard deviation). We show how peatland characteristics dampen the effect of intense rain, and how soil freeze-thaw processes regulate surface and groundwater partitioning during snowmelt. With these results, we demonstrate the importance of defining, understanding and quantifying the role of landscape heterogeneity and sub-catchment characteristics for accurately representing catchment hydrological functioning.

  • 55.
    Teutschbein, Claudia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Grabs, T.homas J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Laudon, Hjalmar
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, SE-90183 Umea, Sweden.
    Karlsen, Reinert H.
    Uppsala Univ, Dept Earth Sci, Villavagen 16, SE-75236 Uppsala, Sweden.
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Uppsala Centre for Sustainable Development, CSD Uppsala, Centre for Environment and Development Studies.
    Simulating streamflow in ungauged basins under a changing climate: The importance of landscape characteristics2018In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 561, p. 160-178Article in journal (Refereed)
    Abstract [en]

    In this paper we explored how landscape characteristics such as topography, geology, soils and land cover influence the way catchments respond to changing climate conditions. Based on an ensemble of 15 regional climate models bias-corrected with a distribution-mapping approach, present and future streamflow in 14 neighboring and rather similar catchments in Northern Sweden was simulated with the HBV model. We established functional relationships between a range of landscape characteristics and projected changes in streamflow signatures. These were then used to analyze hydrological consequences of physical perturbations in a hypothetically ungauged basin in a climate change context. Our analysis showed a strong connection between the forest cover extent and the sensitivity of different components of a catchment's hydrological regime to changing climate conditions. This emphasizes the need to redefine forestry goals and practices in advance of climate change-related risks and uncertainties.

  • 56. Teutschbein, Claudia
    et al.
    Seibert, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bias correction of regional climate model simulations for hydrological climate-change impact studies: Review and evaluation of different methods2012In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 456-457, p. 12-29Article in journal (Refereed)
    Abstract [en]

    Despite the increasing use of regional climate model (RCM) simulations in hydrological climate-change impact studies, their application is challenging due to the risk of considerable biases. To deal with these biases, several bias correction methods have been developed recently, ranging from simple scaling to rather sophisticated approaches. This paper provides a review of available bias correction methods and demonstrates how they can be used to correct for deviations in an ensemble of 11 different RCM-simulated temperature and precipitation series. The performance of all methods was assessed in several ways: At first, differently corrected RCM data was compared to observed climate data. The second evaluation was based on the combined influence of corrected RCM-simulated temperature and precipitation on hydrological simulations of monthly mean streamflow as well as spring and autumn flood peaks for five catchments in Sweden under current (1961-1990) climate conditions. Finally, the impact on hydrological simulations based on projected future (2021-2050) climate conditions was compared for the different bias correction methods. Improvement of uncorrected RCM climate variables was achieved with all bias correction approaches. While all methods were able to correct the mean values, there were clear differences in their ability to correct other statistical properties such as standard deviation or percentiles. Simulated streamflow characteristics were sensitive to the quality of driving input data: Simulations driven with bias-corrected RCM variables fitted observed values better than simulations forced with uncorrected RCM climate variables and had more narrow variability bounds.

  • 57.
    Thomas, Zahra
    et al.
    Agrocampus Ouest, Soil Agro & hydroSyst, UMR 1069, F-35000 Rennes, France..
    Rousseau-Gueutin, Pauline
    Sorbonne Paris Cite, EHESP Rennes, Paris, France..
    Kolbe, Tamara
    Univ Rennes 1, CNRS, Geosci Rennes, UMR 6118, Campus Beaulieu, F-35042 Rennes, France.;Univ Rennes 1, CNRS, OSUR, ECOBIO, Campus Beaulieu, F-35042 Rennes, France..
    Abbott, Benjamin W.
    Univ Rennes 1, CNRS, OSUR, ECOBIO, Campus Beaulieu, F-35042 Rennes, France..
    Marcais, Jean
    Univ Rennes 1, CNRS, Geosci Rennes, UMR 6118, Campus Beaulieu, F-35042 Rennes, France..
    Peiffer, Stefan
    Bayreuth Ctr Ecol & Environm Res, Bayreuth, Germany..
    Frei, Sven
    Bayreuth Ctr Ecol & Environm Res, Bayreuth, Germany..
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pichelin, Pascal
    Agrocampus Ouest, Soil Agro & hydroSyst, UMR 1069, F-35000 Rennes, France..
    Pinay, Gilles
    Univ Rennes 1, CNRS, OSUR, ECOBIO, Campus Beaulieu, F-35042 Rennes, France..
    de Dreuzy, Jean-Raynald
    Univ Rennes 1, CNRS, Geosci Rennes, UMR 6118, Campus Beaulieu, F-35042 Rennes, France..
    Constitution of a catchment virtual observatory for sharing flow and transport models outputs2016In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 543, p. 59-66Article in journal (Refereed)
    Abstract [en]

    Predicting hydrological catchment behavior based on measurable (and preferably widely available) catchment characteristics has been one of the main goals of hydrological modelling. Residence time distributions provide synoptic information about catchment functioning and can be useful metrics to predict their behaviors. Moreover, residence time distributions highlight a wide range of characteristic scales (spatial and temporal) and mixing processes. However, catchment-specific heterogeneity means that the link between residence time distributions and catchment characteristics is complex. Investigating this link for a wide range of catchments could reveal the role of topography, geology, land-use, climate and other factors in controlling catchment hydrology. Meaningful comparison is often challenging given the diversity of data and model structures and formats. To address this need, we are introducing a new virtual platform called Catchment virtual Observatory for Sharing flow and transport models outputs (COnSOrT). The goal of COnSOrT is to promote catchment intercomparison by sharing calibrated model outputs. Compiling commensurable results in COnSOrT will help evaluate model performance, quantify inter-catchment controls on hydrology, and identify research gaps and priorities in catchment science. Researchers interested in sharing or using calibrated model results are invited to participate in the virtual observatory. Participants may test post-processing methods on a wide range of catchment environments to evaluate the generality of their findings.

  • 58. Thorndahl, S.
    et al.
    Beven, Keith
    Institute of Environmental and Natural Sciences, Lancaster University, Lancaster, UK.
    Jensen, J. B.
    Schaarup-Jensen, K.
    Event based uncertainty assessment in urban drainage modelling, applying the GLUE methodology2008In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 357, no 3-4, p. 421-437Article in journal (Refereed)
    Abstract [en]

    In the present paper an uncertainty analysis on an application of the commercial urban drainage model. MOUSE is conducted. Applying the Generalized Likelihood Uncertainty Estimation (GLUE) methodology the model. is conditioned on observation time series from two flow gauges as well as the occurrence of combined sewer overflow. The GLUE methodology is used to test different conceptual setups in order to determine if one model, setup gives a better goodness of fit conditional on the observations than the other. Moreover, different methodological investigations of GLUE are conducted in order to test if the uncertainty analysis is unambiguous. It is shown that the GLUE methodology is very applicable in uncertainty analysis of this application of an urban drainage model, although it was shown to be quite difficult to get good fits of the whole time series. (c) 2008 Elsevier B.V. All rights reserved.

  • 59. Vigiak, Olga
    et al.
    Romanowicz, Renata J
    van Loon, Emiel E
    Sterk, Gert
    Beven, Keith
    A disaggregating approach to describe overland flow occurrence within a catchment2006In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 323, no 1-4, p. 22-40Article in journal (Refereed)
    Abstract [en]

    A parametrically parsimonious, data-based model was built on observations at hillslope and catchment scale to simulate the distribution of overland flow within a small East African Highlands catchment (Kwalei, Tanzania). A rainfall-flow Data Based Mechanistic model identified catchment effective rainfall and separated the discharge quick flow, interpreted as the combination of overland flow plus reinfiltration along the slopes, and the slow flow, interpreted as ground water displacement. Observations of overland flow occurrence along the slopes were used to derive probability distribution functions (pdfs) of overland flow in relation to effective rainfall for two pre-defined hydrologic response units (HRUs): perennial (HRU_1) versus other crops (HRU_2). At low effective rainfall, overland flow was more frequent in HRU_2, while at high effective rainfall overland flow in the two HRUs was similar. The pdfs were employed to disaggregate the quick flow into HRU overland flow depth. Reinfiltration was accounted for by assuming that only the overland flow generated in the lower part of the field would drain downslope. Effective reinfiltration length was about 4 m. Comparison of model simulations versus Gerlach trough measurements indicated that rainfall intensity was not accounted for sufficiently. The use of smaller time steps or, alternatively, of a rainfall intensity threshold could improve model performance. However, given the high variability of overland flow observed along the slopes and the limited dataset, model simulations were considered satisfactory. Though the model needs further testing on other datasets, the disaggregating approach represents an inductive alternative to the use of infiltration equations to model overland flow within a catchment. (c) 2005 Elsevier B.V. All rights reserved.

  • 60. Viglione, Alberto
    et al.
    Di Baldassarre, Giuliano
    Brandimarte, Luigia
    Kuil, Linda
    Carr, Gemma
    Scolobig, Anna
    Bloeschl, Guenter
    Insights from socio-hydrology modelling on dealing with flood risk–roles of collective memory, risk-taking attitude and trust2014In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 518, no PartA, p. 71-82Article in journal (Refereed)
  • 61. Viviroli, Daniel
    et al.
    Seibert, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Can a regionalized model parameterisation be improved with a limited number of runoff measurements?2015In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 529, p. 49-61Article in journal (Refereed)
    Abstract [en]

    Application of hydrological models to ungauged basins is both a highly relevant and challenging task. While research has brought forth various approaches for inferring or transferring tuneable model parameters from gauged and calibrated catchments, it has also been recently shown that a few short measurements can support predictions in an ungauged basin by constraining the acceptable range of the parameters. For the present study, we examined a combination of both parameter regionalisation and short-term runoff measurements. More precisely, we attempted to select complete parameter sets from a range of calibrated catchments using a few measurements. Then, we tested a number of ways to combine the hydrographs simulated with these parameter sets with those simulated using a well-established Nearest Neighbour scheme, in order to make use of both actually measured runoff data as well as hydrological similarity. The experimental basis for our study were 49 representative catchments in Switzerland which have been successfully calibrated and regionalised with the hydrological modelling system PREVAH. Results show that even a few short measurements during mean runoff conditions can lead to models that are more efficient than those achieved with hydrological similarity alone. The possible improvement depends largely on the regime type of the catchment examined. Also, the most suitable season to perform measurements varies: In catchments dominated by snow melt or ice melt or both, considerable improvements can be achieved with as few as two measurements during spring or summer, whereas rainfall-dominated catchments show only moderate improvements with no particular season being more suitable for the measurements. Our findings highlight the value of field measurements in mountain areas. The information gained in these regions from short measurements may act as a counterbalance to the sparse operational observation networks. (C) 2015 Elsevier B.V. All rights reserved.

  • 62.
    Vrugt, Jasper A.
    et al.
    Univ Calif Irvine, Dept Civil & Environm Engn, Irvine, CA USA; Univ Calif Irvine, Dept Earth Syst Sci, Irvine, CA USA; Univ Amsterdam, IBED, Amsterdam, Netherlands.
    Beven, Keith
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Univ Lancaster, Lancaster Environm Ctr, Lancaster, England; London Sch Econ, CATS, London, England.
    Embracing equifinality with efficiency: Limits of Acceptability sampling using the DREAM(LOA) algorithm2018In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 559, p. 954-971Article in journal (Refereed)
    Abstract [en]

    This essay illustrates some recent developments to the DiffeRential Evolution Adaptive Metropolis (DREAM) MATLAB toolbox of Vrugt (2016) to delineate and sample the behavioural solution space of set-theoretic likelihood functions used within the GLUE (Limits of Acceptability) framework (Beven and Binley, 1992, 2014; Beven and Freer, 2001; Beven, 2006). This work builds on the DREAM(ABC) algorithm of Sadegh and Vrugt (2014) and enhances significantly the accuracy and CPU-efficiency of Bayesian inference with GLUE. In particular it is shown how lack of adequate sampling in the model space might lead to unjustified model rejection.

  • 63.
    Wetterhall, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Halldin, Sven
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Xu, Chong-Yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Statistical precipitation downscaling in central Sweden with the analogue method2005In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 306, no 1-4, p. 174-190Article in journal (Refereed)
    Abstract [en]

    Most climate predictions show significant consequences globally and regionally, but many of its critical impacts will occur at sub-regional and local scales. Downscaling methods are, thus, needed to assess effects of large-scale atmospheric circulation on local parameters such as precipitation and runoff. This study aims at evaluating the analogue method (AM) as a benchmark method for precipitation downscaling in northern Europe. The predictors used in this study were daily and monthly gridded sea-level pressures from 1960 to 1997 in an area 45-75 degrees N and 30 degrees W-40 degrees E with a resolution of 5 X 5 degrees long-lat. Analogues for daily and monthly precipitation at seven precipitation stations in south-central Sweden were established with two techniques, principal-component analysis (PCA) and the Teweles-Wobus score (TWS). The results showed that AM downscaling on both daily and monthly basis was commonly generally much better than a random baseline but depended on the objective function used for assessment; PCA and TWS produced similar results in most cases but TWS was superior in simulating precipitation duration and intensity. Downscaling was improved when seasonality was included and when the SLP field was confined to those geographical areas that contributed most to precipitation in south-central Sweden.

  • 64.
    Widén-Nilsson, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Halldin, Sven
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Xu, Chong-yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Global water-balance modelling with WASMOD-M: parameter estimation and regionalisation2007In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 340, no 1-2, p. 105-118Article in journal (Refereed)
    Abstract [en]

    Limitations in water quantity and quality are among the greatest social and economic problems facing mankind. However, difficulties in estimating the global long-term average runoff have led to differences of as much as 30% when integrated to the whole earth. Model estimates of runoff are especially uncertain for the 50% of the global land surface lacking consistent runoff data. In this study, we present the WASMOD-M global water-balance model, constructed to provide robust runoff estimates both for gauged and ungauged basins. WASMOD-M is a conceptual water-budgeting model with two state-variables and five tunable parameters. A simple parameter-value estimation procedure allowed “acceptable” parameter values to be identified both for the majority of gauged basins, and for most ungauged basins. Acceptable global simulations could be accomplished with continentally constant parameter values but at the cost of compensating errors on a basin scale. A “standard”, spatially-distributed parameter-value set was derived for a ”best” global simulation. Of the simulated 59132 0.5° × 0.5° cells, 45% got “good” parameter values as a by-product of regionalisation, 41% from regionalisation, whereas 14% were given a default value set. This global set allowed simulation of the 1915–2000 world water balance. The simulation was in the same range as previously published model results and compilations of runoff measurements. Long-term average within-year runoff variations agreed well with previously published results for most of the studied runoff stations although WASMOD-M was only calibrated against long-term average runoff. Improvement of WASMOD-M and other global water-balance models should be simplified by a common definition of basin boundaries and areas, as well as runoff. Further, modelling progress will depend on improved global datasets of precipitation and runoff regulation.

  • 65.
    Xu, Chong-yu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Gong, Lebing
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Jiang, T.
    Chen, D.
    Singh, V. P.
    Analysis of spatial distribution and temporal trend of reference evapotranspiration and pan evaporation in Changjiang (Yangtze River) catchment2006In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 327, no 1-2, p. 81-93Article in journal (Refereed)
    Abstract [en]

    In this study the Penman–Monteith reference evapotranspiration, pan evaporation measured by a 20 cm pan, and pan coefficient, i.e., the ratio of Penman–Monteith evapotranspiration to pan evaporation, at 150 meteorological stations during 1960–2000 in the Changjiang (Yangtze River) catchment in China are calculated, compared and regionally mapped. Their spatial distributions and temporal variations are examined and the causes for the variations are discussed. The spatial distributions of temporal trends in the reference evapotranspiration as well as in the meteorological variables that determine evapotranspiration are analyzed. The contributions of various meteorological variables to the temporal trend detected in the reference evapotranspiration and pan evaporation are then determined. The results show that: (1) the spatial distributions of reference evapotranspiration and pan evaporation are roughly similar. Spatial correlation coefficients between the reference evapotranspiration and the pan evaporation are high for both the seasonal and annual values. The temporal correlation between the two estimates is higher in the lower (humid) region than in the upper (semi-arid) region. The spatial distribution pattern of the pan coefficient is significantly influenced by wind speed and relative humidity in the region. Higher values of the pan coefficient were found in the central area of the catchment with a relatively high humidity (as compared with the upper area) and a very low wind speed (as compared with other areas); (2) for the whole catchment, there is a significant decreasing trend in both the reference evapotranspiration and the pan evaporation, which is mainly caused by a significant decrease in the net total radiation and to a lesser extent by a significant decrease in the wind speed over the catchment. No temporal trend is detected for the pan coefficient; (3) sensitivity analysis shows that the reference evapotranspiration is most sensitive to the net total radiation, followed by relative humidity, air temperature and wind speed.

  • 66.
    Xu, Chong-yu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Singh, V. P.
    Evaluation of three complementary relationship evapotranspiration models by water balance approach to estimate actual regional evapotranspiration in different climatic regions2005In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 308, no 1-4, p. 105-121Article in journal (Refereed)
  • 67.
    Xu, Chong-yu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Tunemar, Liselotte
    Chen, Yongqin David
    Singh, V. P.
    Evaluation of seasonal and spatial variations of lumped water balance model sensitivity to precipitation data errors2006In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 324, no 1-4, p. 80-93Article in journal (Refereed)
    Abstract [en]

    Sensitivity of hydrological models to input data errors have been reported in the literature for particular models on a single or a few catchments. A more important issue, i.e. how model's response to input data error changes as the catchment conditions change has not been addressed previously. This study investigates the seasonal and spatial effects of precipitation data errors on the performance of conceptual hydrological models. For this study, a monthly conceptual water balance model, NOPEX-6, was applied to 26 catchments in the Mälaren basin in Central Sweden. Both systematic and random errors were considered. For the systematic errors, 5–15% of mean monthly precipitation values were added to the original precipitation to form the corrupted input scenarios. Random values were generated by Monte Carlo simulation and were assumed to be (1) independent between months, and (2) distributed according to a Gaussian law of zero mean and constant standard deviation that were taken as 5, 10, 15, 20, and 25% of the mean monthly standard deviation of precipitation. The results show that the response of the model parameters and model performance depends, among others, on the type of the error, the magnitude of the error, physical characteristics of the catchment, and the season of the year. In particular, the model appears less sensitive to the random error than to the systematic error. The catchments with smaller values of runoff coefficients were more influenced by input data errors than were the catchments with higher values. Dry months were more sensitive to precipitation errors than were wet months. Recalibration of the model with erroneous data compensated in part for the data errors by altering the model parameters.

  • 68. Yang, Tao
    et al.
    Shao, Quanxi
    Hao, Zhen-Chun
    Chen, Xi
    Zhang, Zengxin
    Xu, Chong-Yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sun, Limin
    Regional frequency analysis and spatio-temporal pattern characterization of rainfall extremes in the Pearl River Basin, China2010In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 380, no 3-4, p. 386-405Article in journal (Refereed)
    Abstract [en]

    This paper presents a method for regional frequency analysis and spatio-temporal pattern characterization of rainfall-extreme regimes (i.e. extremes, durations and timings) in the Pearl River Basin (PRB) using the well-known L-moments approach together with advanced statistical tests including stationarity test and serial correlation check, which are crucial to the valid use of L-moments for frequency analysis. Results indicate that: (1) the entire Pearl River Basin (40 sites) can be categorized into six regions by cluster analysis together with consideration of the topography and spatial patterns of mean precipitation in the basin. The results of goodness-of-fit measures indicate that the GNO, GLO, GEV, and PE3 distributions fit well for most of the basin for different HOM regions, but their performances are slightly different in term of curve fitting; (2) the estimated quantiles and their biases approximated by Monte Carlo simulation demonstrate that the results are reliable enough for the return periods of less than 100 years; (3) excessive precipitation magnitude records are observed at Guilin region of Guangxi Province and Fogang region of Guangdong Province, which have sufficient climate conditions (e.g. precipitation and humidity) responsible for the frequently occurred flood disasters in the regions. In addition, the spatial variations of precipitation in different return periods (Return period = 1, 10, 50 years to 100 years) increase from the upstream to downstream at the regional scale; (4) the seasonal patterns of precipitation extremes for different topographical regions are different. The major precipitation events of AM1R, AM3R, AM5R and AM7R in regions of low-elevation in lower (south-eastern) part of the basin occur mainly in May, June, July and August, while the main precipitation periods for the mountainous region upstream are June, July and August. Further analysis of the NCAR/NCEP reanalysis data indicates that the eastern Asian summer monsoon and typhoons (or hurricanes) are major metrological driving forces on the precipitation regimes. Additionally, topographical features (i.e. elevation, distance to the sea, and mountain’s influences) also exert different impacts on the spatial patterns of such regimes. To the best of our knowledge, this study is the first attempt to conduct a systematic regional frequency analysis on various annual precipitation extremes (based on consecutive 1-, 3-, 5-, 7-day averages) and to establish the possible links to climate pattern and topographical features in the Pearl River Basin and even in China. These findings are expected to contribute to exploring the complex spatio-temporal patterns of extreme rainfall in this basin in order to reveal the underlying linkages between precipitation and floods from a broad geographical perspective. (C) 2009 Published by Elsevier B.V.

  • 69. Ye, Xuchun
    et al.
    Zhang, Qi
    Liu, Jian
    Li, Xianghu
    Xu, Chong-yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Distinguishing the relative impacts of climate change and human activities on variation of streamflow in the Poyang Lake catchment, China2013In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 494, p. 83-95Article in journal (Refereed)
    Abstract [en]

    Under the background of global climate change and local anthropogenic stresses, many regions of the world have suffered from frequent droughts and floods in recent decades. Assessing the relative effect of climate change and human activities is essential not only for understanding the mechanism of hydrological response in the catchment, but also for local water resources management as well as floods and droughts protection. The Poyang Lake catchment in the middle reaches of the Yangtze River has experienced significant changes in hydro-climatic variables and human activities during the past decades and therefore provides an excellent site for studying the hydrological impact of climate change and human activities. In this study, the characteristics of hydro-climatic changes of the Poyang Lake catchment were analyzed based on the observed data for the period 1960-2007. The relative effect of climate change and human activities was first empirically distinguished by a coupled water and energy budgets analysis, and then the result was further confirmed by a quantitative assessment. A major finding of this study is that the relative effects of climate change and human activities varied among sub-catchments as well as the whole catchment under different decades. For the whole Poyang Lake catchment, the variations of mean annual streamflow in 1970-2007 were primarily affected by climate change with reference to 1960s, while human activities played a complementary role. However, due to the intensified water utilization, the decrease of streamflow in the Fuhe River sub-catchment in 2000s was primarily affected by human activities, rather than climate change. For the catchment average water balance, quantitative assessment revealed that climate change resulted in an increased annual runoff of 75.3-261.7 mm in 1970s-2000s for the Poyang Lake catchment, accounting for 105.0-212.1% of runoff changes relative to 1960s. However, human activities should be responsible for the decreased annual runoff of 5.4-56.3 mm in the other decades, accounting for -5.0% to -112.1% of runoff changes. It is noted that the effects of human activities including soil conservation, water conservancy projects and changes in land cover might accumulate or counteract each other simultaneously, and attempts were not made in this paper to further distinguish them.

  • 70. Zhang, Q.
    et al.
    Liu, C. L.
    Xu, Chong-Yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Xu, Y. P.
    Jiang, T.
    Observed trends of annual maximum water level and streamflow during past 130 years in the Yangtze River basin, China2006In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 324, no 1-4, p. 255-265Article in journal (Refereed)
    Abstract [en]

    Annual maximum streamflow and annual maximum water level and their variations exert most serious influences on human society. In this paper, temporal trends and frequency changes at three major stations of Yangtze River, i.e. Yichang, Hankou and Datong representing upper, middle and lower reaches, respectively, were detected with the help of parametric t-test, Mann-Kendall (MK) analysis and wavelet transform methods. The results show that: (1) there is a significant upward trend in streamflow at middle Yangtze River, indicating that flood hazard in the middle reach of the river, the flood rich region, will be more serious; (2) there is a consistent increase of water level from upper to lower reaches of the river which does not always coincide with the maximum streamflow variations; and (3) the periods of water level changes are decreasing over time, indicating the increasing occurrence frequency of annual maximum water level over time. This phenomenon is more obvious from upper Yangtze River to the lower Yangtze River. Human activities like destruction of vegetation, land reclamation and construction of levees reduced lake sizes and filled up the river bed, reducing the flood storage capacity of lakes and fluvial channel. These factors led to higher water level even some times the streamflow is small. Human should adjust his activity to enhance his adaptive capacity to flood hazard in the future.

  • 71. Zhang, Q.
    et al.
    Xu, Chong-yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Becker, S.
    Jiang, T.
    Sediment and runoff changes in the Yangtze River basin during past 50 years2006In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 311, no 3-4, p. 511-523Article in journal (Refereed)
    Abstract [en]

    Annual runoff and annual suspended sediment loads of hydrological gauging stations along the mainstream of the Yangtze River basin (Pingshan station, Yichang station, Hankou station and Datong station) and main tributaries (Beipei station in Jialingjiang River, Wulong station in Wujiang River and Huangzhuang station in Hanjiang River) were analyzed with the help of Mann–Kendall trend analysis and linear regression analysis. Research results indicate that (1) changing patterns of runoff and sediment loads are different in different parts of the Yangtze River basin. No significant trend is detected for annual runoff at all stations at >95% confidence level. Changes of sediment loads, however, demonstrate different pictures in the Yangtze River basin. The sediment loads are in increasing trend in Pingshan station- the most upstream station on the Yangtze River basin (this increasing trend is significant at >95% confidence level after about 1990), but are in decreasing trend at other stations (including stations in the tributaries studied in this paper). This decreasing trend becomes more obvious from Yichang station to Datong station. (2) Water reservoirs exerted more influences on changes of sediment loads than on runoff, which is the main reason for the decreasing trend of sediment loads found in most stations. (3) Influences of water reservoirs on sediment loads are more obvious in the tributaries than in the mainstream of the Yangtze River basin, while in the mainstream the variation patterns of sediment loads are determined by multiple factors.

  • 72. Zhang, Q.
    et al.
    Xu, Chong-yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Jiang, T.
    Wu, Y.
    Possible influence of ENSO on annual maximum streamflow of the Yangtze River, China2007In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 333, no 2-4, p. 265-277Article in journal (Refereed)
    Abstract [en]

    Variability and possible teleconnections between annual maximum streamflow from the lower, the middle and the upper Yangtze River basin and El Niño/Southern Oscillation (ENSO) are detected by continuous wavelet transform (CWT), cross-wavelet and wavelet coherence methods. The results show that: (1) different phase relations are found between annual maximum streamflow of the Yangtze River and El Niño/Southern Oscillation (ENSO) in the lower, the middle and the upper Yangtze River basin. In-phase relations are detected between annual maximum streamflow of the lower Yangtze River and anti-phase relations are found in the upper Yangtze River. But ambiguous phase relations occur in the middle Yangtze River, showing that the middle Yangtze River basin is a transition zone. Different climatic systems control the upper and the lower Yangtze River. The upper Yangtze River is mainly influenced by the Indian summer monsoon and the lower Yangtze is mainly influenced by the East Asian summer monsoon; (2) as for the individual stations, different phase relations are found in the longer and the shorter periods, respectively. In the longer periods, the annual maximum streamflow is more influenced by climatic variabilities, while in the shorter periods, it is influenced by other factors, e.g. human activities. The results of the study provide valuable information for improving the long-term forecasting of the streamflow using its relationship with ENSO and the Indian Monsoon.

  • 73. Zhang, Qiang
    et al.
    Xu, Chong-Yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Chen, David
    Jiang, Jianmin
    Abrupt behaviors of the streamflow of the Pearl River basin and implications for hydrological alterations across the Pearl River Delta, China2009In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 377, p. 274-283Article in journal (Refereed)
    Abstract [en]

    In this study, we analyze the long streamflow series of three hydrological stations of the lower Pearl River basin and the streamflow ratio between Makou and Sanshui stations by using statistical techniques. Furthermore, we also attempt to address influences of precipitation and human activities (human-induced deepening of river channels) on streamflow ratio. The results indicate that: (1) the streamflow variations show remarkable relations with precipitation changes in West and East River basins, implying tremendous influences of climate changes on hydrological processes. Decreasing precipitation was observed in North River basin. However, the streamflow, amount of the Sanshui station largely increased due to enlarged streamflow allocation from the West River to the North River; (2) increasing streamflow ratio of Sanshui/(Makou + Sanshui) is the result of morphological changes (downcut) of river channels in the upper Pearl River Delta. The fast downcut of river channels is mainly due to intensive sand mining. Larger magnitude of increase in streamflow ratio corresponds well to the higher intensity of in-channel sand dredging; (3) after late-1990s, decreasing precipitation of the Pearl River basin abates the streamflow amount and also the streamflow ratio. The influences of human activities and climate changes are varying in different time intervals and in different river basins. Due to tremendous impacts of increased streamflow ratio between Sanshui and Makou station. relations between streamflow and precipitation relations in the North River basin are not statistically good. This study helps to improve understandings of the causes underlying altered streamflow variations in the lower Pearl River basin and the hydrological alterations within the Pearl River Delta region. (C) 2009 Elsevier B.V. All rights reserved.

  • 74. Zhang, Qiang
    et al.
    Xu, Chong-Yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Singh, P
    Yang, Tao
    Multiscale variability of sediment load and streamflow of the lower Yangtze River basin: Possible causes and implications2009In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 368, p. 96-104Article in journal (Refereed)
    Abstract [en]

    Long monthly streamflow and sediment load series observed at the Datong station located in the lower Yangtze River basin were analyzed using the scanning t-test, F-test and coherency analysis techniques. The results indicated that: (1) different changing properties of the first and the second moments of the hydrological series on different time scales were observed, reflecting different driving factors influencing the hydrological processes of the lower Yangtze River basin; (2) a generally decreasing trend can be identified after the mid-1980s. Significant abrupt changes in sediment load were analyzed in the sediment load series. However, more complicated changing patterns can be observed in the changes in streamflow. Generally decreasing sediment load and increasing streamflow gave rise to anti-phase relations between sediment load and the streamflow on longer time scales. In-phase relations between sediment load and streamflow, on shorter time scales may imply a considerable influence of the hydrological dynamics on sediment transport; and (3) human activities, particularly the construction of water storage reservoirs, exerted a massive influence on sediment load variations. Construction of a large amount of water reservoirs on the tributaries of the Yangtze River and the Gezhouba Dam on the mainstem of the Yangtze River seem to be the main factors responsible for abrupt changes in the sediment load. Construction of the Three Gorges Dam causes a sharp decrease and unstable variability in sediment load variations, which may pose new challenges for the ecological environment conservation and the deltaic management of the Yangtze Delta region. (c) 2009 Elsevier B.V. All rights reserved.

  • 75. Zhang, Qiang
    et al.
    Xu, Chong-Yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Zhang, Zengxin
    Chen, Yongqin David
    Liu, Chun-ling
    Lin, Hui
    Spatial and temporal variability of precipitation maxima during 1960-2005 in the Yangtze River basin and possible association with large-scale circulation2008In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 353, no 3-4, p. 215-227Article in journal (Refereed)
    Abstract [en]

    This study investigated spatial and temporal patterns of trends of the precipitation maxima (defined as the annual./seasonal. maximum precipitation) in the Yangtze River basin for 1960-2005 using Mann-Kendall trend test, and explored association of changing patterns of the precipitation maxima with large-scale circulation using NCEP/NCAR reanalysis data. The research results indicate changes of precipitation maxima from relative stable patterns to the significant increasing/decreasing trend in the middle 1970s. With respect to annual variability, the rainy days are decreasing and precipitation intensity is increasing, and significant increasing trend of precipitation intensity was detected in the middle and lower Yangtze River basin. Number of rain days with daily precipitation exceeding 95th and 99th percentiles and related precipitation intensities are in increasing tendency in summer. Large-scale atmospheric circulation analysis indicates decreasing strength of East Asian summer monsoon during 1975-2005 as compared to that during 1961-1974 and increasing geopotential height in the north China, South China Sea and west Pacific regions, all of which combine to negatively impact the northward propagation of the vapor flux. This circulation pattern will be beneficial for the longer stay of the Meiyu front in the Yangtze River basin, leading to more precipitation in the middle and lower Yangtze River basin in summer months. The significant increasing summer precipitation intensity and changing frequency in the rain/no-rain days in the middle and lower Yangtze River basin have potential to result in higher occurrence probability of flood and drought hazards in the region.

  • 76. Zhang, Zengxin
    et al.
    Chen, Xi
    Xu, Chong-Yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Hong, Yang
    Hardy, Jill
    Sun, Zhonghua
    Examining the influence of river-lake interaction on the drought and water resources in the Poyang Lake basin2015In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 522, p. 510-521Article in journal (Refereed)
    Abstract [en]

    In recent years, the Poyang Lake basin is in a prolonged drought which has placed immense pressure on the water resources utilization. In this paper, we explore the spatial and temporal distributions of extreme droughts in the Poyang Lake basin by using the methods of SPI (Standardized Precipitation Index) and EOF (Empirical Orthogonal Function) for the period of 1956-2009, which are influenced by regional precipitation anomalies and river-lake interaction due to water impounding of the Three Gorges Dam (TGD). The results show that: (I) the Poyang Lake basin experienced six extreme droughts during the past 60 years, which lead to decreases in streamflow from five tributary rivers down to the Poyang Lake. The droughts in the 1960s and the 2000s were the most serious ones. However, there was an increasing trend of streamflow in the upper and middle Yangtze in the 1960s, and a decreasing trend appeared in the 2000s. The decline of streamflow in the upper Yangtze reaches has lowered the water level of lower Yangtze River which has-caused more outflow from the Poyang Lake to the Yangtze River; (2) the operation of the Three Gorges Dam (TGD) has altered the seasonal pattern of flow regimes in the Poyang Lake and significantly reduced the water level in the lower Yangtze River during the TGD impounding period from late September to early November; and (3) the conjunction of extreme droughts in the Poyang lake and the upper Yangtze reaches coincided with the impounding of the TGD is the main cause of the low water level in the Poyang Lake. Although the impact of the recent droughts in the Poyang Lake and upper Yangtze reaches has played a crucial role in the low water level of Poyang lake, more attention should be paid to its sensitivity to the influence of the large dam-induced changes in the interaction between river and lake, particularly during impounding periods.

  • 77. Zhang, Zengxin
    et al.
    Chen, Xi
    Xu, Chong-Yu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Yuan, Lifeng
    Yong, Bin
    Yan, Shaofeng
    Evaluating the non-stationary relationship between precipitation and streamflow in nine major basins of China during the past 50 years2011In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 409, no 1-2, p. 81-93Article in journal (Refereed)
    Abstract [en]

    In this paper, the trends of the annual streamflow and precipitation and cross correlations between them were analyzed in nine large river basins of China during 1956-2005. The results indicate that: (1) the annual mean streamflow decreases in arid and semi-arid regions of north China; however, increasing trends occur in south and Southwest China; (2) the annual streamflow and precipitation exhibit reasonable correlation in nine large river basins except those located in inland areas. The annual streamflow over most areas of China is fed by precipitation; however, the decline in streamflow is faster than the decreases of precipitation since 1970s in the arid and semi-arid regions of north China. The relationship between the annual precipitation and streamflow presents a non-stationary state in north China. This non-stationary relationship is strongly influenced by both human activities and precipitation changes; (3) a significant increase of water use might be the major factor responsible for the steeper decline in streamflow than in precipitation in Haihe River, Yellow River and Songliao River basins in north China. In inland river areas, increase of water use and actual evapotranspiration might result in decline in streamflow although precipitation has an increase tendency. This paper sheds light on the non-stationary relationship between annual precipitation and streamflow and possible underlying causes, which will be helpful for a better understanding of the changes of precipitation and streamflow in China at large scale and in other regions of the world.

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