Istvan Bogardi | University of Nebraska Lincoln (original) (raw)

Papers by Istvan Bogardi

Journal of Environmental Engineering-asce, 1991

... Titre du document / Document title. Fuzzy decision making in dredged-material management = Dé... more ... Titre du document / Document title. Fuzzy decision making in dredged-material management = Décision floue pour la gestion de matériel de dragage. Auteur(s) / Author(s). LEE YW (1) ; BOGARDI I. ; STANSBURY J. ; Affiliation(s) du ou des auteurs / Author(s) Affiliation(s). (1) Univ ...

… Engineering Risk Assessment, Nato ASI Series, …, 1991

Journal of the Engineering Mechanics Division

Water

A risk management methodology is presented for the adaptation of water supply to changing climate... more A risk management methodology is presented for the adaptation of water supply to changing climate and land-use activities, considering socio-economic aspects. Several management options were selected for the case of the public water supply of Ljubljana, the capital of Slovenia. The major management actions for improving drinking water safety are (1) land-use limitations within the drinking water protection areas and (2) drinking water treatment. Trends in groundwater level are decreasing, above all in the area of well fields; therefore, artificial recharge and setting up a new independent well field were also considered. The management actions were evaluated according to several criteria, such as water supply risk reduction for the various users (drinking, agricultural, and industrial) and realization of the actions (cost, flexibility, and leg time). For management options, the ranking “Fuzzy Decimaker” tool was applied, which is based on a Multiple Criterion Decision Making (MCDM) ...

Water Science and Technology

International Journal of Climatology, Sep 30, 1995

A fuzzy rule-based methodology is applied to the problem of classifying daily atmospheric circula... more A fuzzy rule-based methodology is applied to the problem of classifying daily atmospheric circulation patterns (CP). The purpose of the approach is to produce a semi-automated classification that combines the expert knowledge of the meteorologist and the speed and objectivity of the computer. Rules are defined corresponding to the geographical location of pressure anomalies. A CP is described by the location of four different possible pressure anomalies. The rules are formulated with fuzzy sets, allowing a certain flexibility because slightly different pressure maps may correspond to a given CI? Accordingly the degree of hlfilment of a rule is defined in order to measure the extent to which a pressure map may indeed belong to a CP type. As an output of the analysis, the CP on any given day is assigned to one, and only one, CP type to a varying degree of credibility. The methodology is applied to a European case study. The subjective classification of European CPs given by Hess and Brezowsky provides a basis for constructing the rules. The classification obtained can be used, for example, to simulate local precipitation conditioned on the 700 hPa pressure field. The information content of the fuzzy classification as measured by precipitation-related indices is similar to that of existing subjective classifications. The fuzzy rule-based approach thus has potential to be applicable to the classification of GCM produced daily CPs for the purpose of predicting the effect of climate change on space-time precipitation over areas where only a rudimentary classification exists or where none at all exists.

A fuzzy rule-based technique is used for modelling the relationship between climatic forcing and ... more A fuzzy rule-based technique is used for modelling the relationship between climatic forcing and droughts in a Central/Eastern European country, Hungary. Two types of climatic forcing-called premises-are considered: atmospheric circulation patterns (CP) and El Niño Southern Oscillation (ENSO). Both the Hess-Brezowsky CP types and ENSO events influence the occurrence of droughts, but the ENSO signal is relatively weak in a statistical sense. The fuzzy rule-based approach is able to learn the high space-time variability of monthly Palmer Drought Severity Index (PDSI) and results in a proper reproduction of the empirical frequency distributions. The "engine" of the approach, the fuzzy rules, are ascertained from a subset called the learning set of the observed time series of premises (monthly CP frequencies and Southern Oscillation Index) and PDSI response. Then an independent subset, the validation set, is used to check how the application of fuzzy rules reproduces the observed PDSI.

Iahs Aish Publication, 1987

Http Dx Doi Org 10 1080 02508068508686327, Jan 22, 2009

ABSTRACT A semi-empirical downscaling approach is presented to estimate spatial and temporal stat... more ABSTRACT A semi-empirical downscaling approach is presented to estimate spatial and temporal statistical properties of local daily mean wind speed under global climate change. The present semi-empirical downscaling method consists of two elements. Since general circulation models (GCMs) are able to reproduce the features of the present atmospheric general circulation quite correctly, the first element represents the large-scale circulation of the atmosphere. The second element is a link between local wind speed and large-scale circulation pattern (CP). The linkage is expressed by a stochastic model conditioned on CP types. Parameters of the linkage model are estimated using observed data series; then this model is utilized with GCM-generated CP type data corresponding to a 2 × CO2 scenario. Under the climate of Nebraska the lognormal distribution is the best two-parameter distribution to describe daily mean wind speed. The space-time variability of wind speed is described by a transformed multivariate autoregressive (AR) process, and the linkage between local wind and large-scale circulation is expressed as a conditional AR process, i.e. the autoregressive parameters depend on the actual daily CP type. The basic tendency of change under 2 × CO2 climate is a considerable increase of wind speed from the beginning of summer to the end of winter and a somewhat smaller wind decrease in spring.

Math Geol, 1990

The geostatistical analysis of soil liner permeability is based on 20 measurements and imprecise ... more The geostatistical analysis of soil liner permeability is based on 20 measurements and imprecise prior information on nugget effect, sill, and range of the unknown variogram. Using this information, membership functions for variogram parameters are assessed and the fuzzy variogram is constructed. Both kriging estimates and estimation variances are calculated as fuzzy numbers from the fuzzy variogram and data points.

Hydrological Sciences Bulletin, 1973

Water resource systems are fraught with stochastic uncertainties and imprecision due to insuffici... more Water resource systems are fraught with stochastic uncertainties and imprecision due to insufficient knowledge. Realistic, plausible and relatively simple models should be found to reflect these characteristics before practitioners would be ready to apply the theory. It is proposed that a joint probabilistic/fuzzy set approach may help in this respect. Thus uncertainty and imprecision in risk analysis, an important area of water resource systems analysis, are to be modeled simultaneously. The case of health risk due to groundwater contamination is considered. Fuzzy set geostatistics can be used to describe imprecision in the spatial variability of exposure; that is, contaminant concentration. The consequence of an exposure is typically described by dose-response relationships, generally based on a few animal experimental data. Fuzzy regression is shown to be applicable for encoding imprecision in such dose-response relationships. More generally, it is shown how risk management can be performed by trading off risk and cost under uncertainty and imprecision, leading to results that decision makers can readily visualize.