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28 - Detecting change in river flow series
- from Part IV - New methods for evaluating effects of land-use change
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- By Z. W. Kundzewicz, Research Centre of Agricultural and Forest Environment, Polish Academy of Sciences, Bukowska 19, 60-809 Poznań, Poland also Potsdam Institute for Climate Impact Research Potsdam, Germany, A. J. Robson, Centre for Ecology and Hydrology, Wallingford, OX10 8BB, UK
- Edited by M. Bonell, L. A. Bruijnzeel, Vrije Universiteit, Amsterdam
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- Book:
- Forests, Water and People in the Humid Tropics
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- 12 January 2010
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- 13 January 2005, pp 703-716
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Summary
INTRODUCTION
Detection of trends in long time series of hydrological data is of paramount scientific and practical importance. Water resources systems are typically designed and operated based on the assumption of stationary hydrology (in particular, an assumption of stationarity of the stochastic proces of river stage or discharge). If this assumption is incorrect then existing procedures for example in the design of levees, dams and reservoirs will have to be revised. Without revision, the systems can be over- or underdesigned and either not serve their purpose adequately or be overly costly.
Studies of change are also of importance because of our need to understand the impact that man is having on the ‘natural’ world. Changes caused directly by man (deforestation, land-use changes, changes in agricultural practices, drainage systems, dam construction, water abstraction, river regulation, urbanisation, etc.) or indirectly via emissions of greenhouse gases, are just a few examples of anthropogenic activities that may be altering important aspects of the hydrological cycle. In addition, natural catchment changes, such as to the channel morphology, can also occur.
The search for climate change signatures in hydrological data has been of much interest recently, driven by the possibility of climate change causing more frequent and severe floods in the future. There are several non-climate mechanisms which may contribute to this effect. Some of them relate to the anthropogenic pressures such as reduction in water resources storage capacity, acceleration of flow in water courses, plus those arising from increasing populations and wealth accumulated in endangered areas.
1 - Hydrological uncertainty in perspective
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- By Z. W. Kundzewicz, Research Centre of Agricultural and Forest Environment Studies, Polish Academy of Sciences, Poznań, Poland
- Edited by Zbigniew W. Kundzewicz, World Meteorological Organization, Geneva
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- Book:
- New Uncertainty Concepts in Hydrology and Water Resources
- Published online:
- 07 May 2010
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- 13 July 1995, pp 3-10
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Summary
ABSTRACT Different aspects and meanings of uncertainty are reviewed. This introductory review forms a basis for putting recent developments in hydrological and water resources applications of uncertainty concepts into perspective. The understanding of the term uncertainty followed herein is a logical sum of all the notions discussed. An attempt is made to justify the structure of the present volume and to sketch the areas of particular contributions in the volume and to point out their connections to different facets of uncertainty.
INTRODUCTION
It seems that there is no consensus within the profession about the very term of uncertainty, which is conceived with differing degrees of generality. Moreover, the word has several meanings and connotations in different areas, that are not always consistent with the colloquial understanding.
In the following section the notions and concepts of uncertainty both beyond and within the water resources research are discussed. Further, particular contributions in this volume are reviewed in the context of their connections to different facets of uncertainty. This is done in the systematic way, following the structure of the book.
NOTIONS OF UNCERTAINTY
Let us take recourse to established dictionaries and see how the words ‘uncertain’ and ‘uncertainty’ are explained. Among the meanings of the word ‘uncertain’, given by Hornby (1974) and Webster's (1987) dictionaries, are the following: not certain to occur, problematical, not certainly knowing or known, doubtful or dubious, not reliable, untrustworthy, not clearly identified or defined, indefinite, indeterminate, changeable, variable (not constant).
5 - Analysis of outliers in Norwegian flood data
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- By L. Gottschalk, Department of Geophysics, University of Oslo, Norway, Z. W. Kundzewicz, Research Centre for Agricultural and Forest Environment Studies, Pol. Acad. Sci., Poznan and Institute of Geophysics, Pol. Acad. Sci., Warsaw, Poland
- Edited by Zbigniew W. Kundzewicz, World Meteorological Organization, Geneva
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- Book:
- New Uncertainty Concepts in Hydrology and Water Resources
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- 07 May 2010
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- 13 July 1995, pp 245-251
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Summary
ABSTRACT Plausibility analysis of annual maximum flows of Norwegian rivers is performed. The data embrace time series of 60 years (1921–80) gathered at 42 observation stations and time series of 30 years (1921–50 and 1951–80) collected at 86 and 83 observation stations, respectively. Six different tests for outliers detection have been used (Shapiro-Wilk, skewness, Student, RST, probability plot coefficient and Anderson-Darling). The tests are based on the assumption of normal distribution, so the normalization (logarithmic or cube root transformation) of the raw data may be a prerequisite. The empirical orthogonal functions approach was used to simulate regional samples with preserved first and second order moments. Outliers analysis of the simulated data was performed and the results were compared with observations.
INTRODUCTION
The existence of outliers in hydrological observation series can possibly explain many of the problems faced in the regional analysis of hydrological data. Figs. 1 and 2 show some examples of hydrographs and probability plots, containing suspicious outliers conceived as observations strongly deviating from the remainder of the data set.
Processing outliers consists of two stages – detection and treatment. Depending on the way the outliers are treated, one can get quite a different representation of the process. In practice outliers are detected and removed in accordance with some intuitive rule. It is so because one finds it difficult to properly choose the theoretical distribution function for an individual observation series and to estimate its parameters. If the parent distribution was known these problems could have been easily solved.
Preface
- Edited by Zbigniew W. Kundzewicz, World Meteorological Organization, Geneva
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- Book:
- New Uncertainty Concepts in Hydrology and Water Resources
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- 07 May 2010
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- 13 July 1995, pp xiii-xiv
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Summary
The present volume contains the edited proceedings of the International Workshop on New Uncertainty Concepts in Hydrology and Water Resources, held in Madralin near Warsaw, Poland from 24 to 26 September 1990. It was organized under the auspices of the Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland, and the International Commission on Water Resources Systems (ICWRS) – a body within the International Association of Hydrological Sciences (IAHS). The Organization and Programme Committee for the Workshop consisted of the following individuals: Professor Lars Gottschalk (Norway/ ICWRS/IAHS), Professor Zdzislaw Kaczmarek (Poland/IIASA), Professor Janusz Kindler (Poland), Professor Zbigniew W. Kundzewicz (Poland), who acted as the Secretary, Professor Uri Shamir (Israel/ICWRS/IAHS) and Professor Witold Strupczewski (Poland).
The Workshop was a continuation of series of meetings organized under the aegis of the International Commission of Water Resources Systems (ICWRS) within the IAHS. This series of meetings was initiated by the former ICWRS President, Professor Mike Hamlin in Birmingham, 1984. Last Workshop of similar character was organized by the ICWRS Secretary, Professor Lars Gottschalk in Oslo (1989).
The Workshop was primarily devoted to recent methods of representation of uncertainty in hydrology and water resources. This embraces newly introduced methods and approaches that, albeit not new, have raised considerable recent interest. In the menu of topics tackled at the Workshop were, among others, such diverse items, as fractals, risk and reliability-related criteria, fuzzy sets, pattern recognition, random fields, time series, outliers detection, nonparametric methods, etc.
6 - Detecting outliers in flood data with geostatistical methods
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- By L. Gottschalk, Department of Geophysics, University of Oslo, Norway, I. Krasovskaia, Hydroconsult AB, Uppsala, Sweden, Z. W. Kundzewicz, Research Centre for Agricultural and Forest Environment Studies, Pol. Acad. Sci., Poznan and Institute of Geophysics, Pol. Acad. Sci., Warsaw, Poland
- Edited by Zbigniew W. Kundzewicz, World Meteorological Organization, Geneva
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- Book:
- New Uncertainty Concepts in Hydrology and Water Resources
- Published online:
- 07 May 2010
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- 13 July 1995, pp 206-214
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Summary
ABSTRACT The plausibility analysis of the regional flood data of Southern Norway is performed with the help of geostatistical methods. As the data at a number of sites are analyzed, one can account the spatial relationships in the outliers detection problem. That is the results of outliers detection may differ in comparison to the non-structured (univariate) case. The geostatistical methods applied are block kriging and Switzer's location-specific covariance analysis, with catchment areas accounted.
INTRODUCTION
An intuitive definition of an outlier can be ‘an observation which deviates so much from other observations as to arise suspicions that it was generated by a different mechanism’ (Hawkins, 1980). An outlying observation can be interpreted in several ways. It may represent an event of extreme magnitude (e.g. due to rare natural causes) that has unexpectedly happened in the system. In flood frequency analysis such extreme events are of outmost importance, indicating a heavy right tail of the parent distribution. On the other hand, a value differing from the remainder of the data set may be an erroneous observation. This could have been caused by instrument malfunctioning or human mistakes (e.g. at the stage of interpretation of the rating curve for high flows). In this latter case outliers may contaminate the data and reduce the useful information about the natural process.
Detection of outliers in hydrological data can be performed in a number of ways. Kottegoda (1984) considered approaches based either on distributional, mixture, or slippage alternatives for investigation of a series of maximum annual flows.
4 - Reliability-related criteria in water supply system studies
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- By Z. W. Kundzewicz, Institute of Geophysics, Polish Academy of Sciences, Warsaw, and Research Centre of Agricultural and Forest Environment Studies, Poznań, Poland, A. Łaski, HYDROPROJEKT Consulting Engineers, Warsaw, Poland
- Edited by Zbigniew W. Kundzewicz, World Meteorological Organization, Geneva
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- Book:
- New Uncertainty Concepts in Hydrology and Water Resources
- Published online:
- 07 May 2010
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- 13 July 1995, pp 299-305
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Summary
ABSTRACT In the study of water supply system expansion in two areas of Poland, the design of a number of water storage reservoirs is considered. The reliability studies reported are based on a system simulation performed for a historical time series of observations of river flows, with and without the hypothetical reservoirs, for future water demands given in two variants. Periods of non-satisfactory and of satisfactory system performance and values of maximum and of cumulative deficits are analyzed. Frequency, duration and severity of nonsatisfactory system performance are assessed as reliability, resilience, and vulnerability. Assumption of exponential distribution of periods of non-satisfactory and satisfactory performance allows straightforward links between several criteria to be established.
INTRODUCTION
In order to evaluate various aspects of non-satisfactory performance of a technical, or natural system, it is necessary to use multiple performance criteria. The use of a set of criteria to describe the possible variants, scenarios and policies offers a perspective that cannot be achieved with a single objective.
The criteria of concern pertain to time-related characteristics (duration and frequency) of the non-satisfactory system performance and also to the amplitude-related characteristics (maximum instantaneous entry into the state of nonsatisfactory performance and the cumulated entry). The ultimate criteria, combining both above types of characteristics measure various aspects of severity and consequences of the non-satisfactory performance.
3 - Hydrological uncertainty – floods of Lake Eyre
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- By V. Kotwicki, Water Resources Branch, Engineering and Water Supply Department, Adelaide, Australia, Z. W. Kundzewicz, Research Centre of Agricultural and Forest Environment Studies, Pol. Acad. Sci., Poznań and Institute of Geophysics, Pol. Acad. Sci., Warsaw, Poland
- Edited by Zbigniew W. Kundzewicz, World Meteorological Organization, Geneva
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- Book:
- New Uncertainty Concepts in Hydrology and Water Resources
- Published online:
- 07 May 2010
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- 13 July 1995, pp 32-38
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ABSTRACT The uncertainty aspects of the process of floods of Lake Eyre are examined. The available records of floods cover the time span of 40 years only. As longer time series of precipitation records are available, one has extended the observed series of inflows to Lake Eyre with the help of a rainfall–runoff model. Further reconstruction of the inflow series has been achieved with the help of proxy data of coral fluorescence intensity. However the limitations of these extensions and reconstructions of inflows are severe. The process of inflows to Lake Eyre could be considered one of the most convincing manifestations of hydrological uncertainty.
LAKE EYRE AND ITS BASIN
Lake Eyre, a large depression in arid Australia, rarely filled with water, attracts the interest of limnologists, hydrologists, geomorphologists and ecologists all over the world. The process of inflows to Lake Eyre has been recently studied by Kotwicki (1986). The following general information draws from the data assembled there.
The Lake Eyre basin (Fig. 1) spreads over 1.14 million km2 of arid central Australia. Almost half of the basin area receives as little rainfall as 150 mm per year or less. The higher rainfalls of the order of 400 mm per year occur in the northern and eastern margins of the basin, influenced by the southern edges of the summer monsoon.