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Institute: search.filters.UBSInstitut.Institut für Wasser- und UmweltsystemmodellierungStart date: 2020Author: search.filters.author.El Hachem, Abbas

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Now showing 1 - 3 of 3
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    Technical note: Space-time statistical quality control of extreme precipitation observations
    (2022) El Hachem, Abbas; Seidel, Jochen; Imbery, Florian; Junghänel, Thomas; Bárdossy, András
    Information about precipitation extremes is of vital importance for many hydrological planning and design purposes. However, due to various sources of error, some of the observed extremes may be inaccurate or false. The purpose of this investigation is to present quality control of observed extremes using space–time statistical methods. To cope with the highly skewed rainfall distribution, a Box–Cox transformation with a suitable parameter was used. The value at the location of a potential outlier is estimated using the surrounding stations and the calculated spatial variogram and compared to the suspicious observation. If the difference exceeds the threshold of the test, the value is flagged as a possible outlier. The same procedure is repeated for different temporal aggregations in order to avoid singularities caused by convection. Detected outliers are subsequently compared to the corresponding radar and discharge observations, and finally, implausible extremes are removed. The procedure is demonstrated using observations of sub-daily and daily temporal resolution in Germany.
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    The use of personal weather station observations to improve precipitation estimation and interpolation
    (2021) Bárdossy, András; Seidel, Jochen; El Hachem, Abbas
    In this study, the applicability of data from private weather stations (PWS) for precipitation interpolation was investigated. Due to unknown errors and biases in these observations, a two-step filter was developed that uses indicator correlations and event-based spatial precipitation patterns. The procedure was tested and cross validated for the state of Baden-Württemberg (Germany). The biggest improvement is achieved for the shortest time aggregations.
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    Spatial extent of precipitation extremes in hydrology
    (Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2023) El Hachem, Abbas; Bárdossy, András (Prof. Dr. rer. nat. Dr.-Ing.)
    Precipitation extremes are a space-time phenomenon that influences many engineering design decisions. The occurrence of precipitation extremes is, however, rare and with values that can deviate notably from ”normal” observations. For design purposes, an estimate of areal rainfall depth for a corresponding return period is needed. Traditionally, point rainfall extreme value statistics are transferred to areal statistics using the concept of area reduction factors. These are, in general, based on simple assumptions without considering the effects of climate change. Area Depth Duration Frequency (ADDF) curves are a mathematical function relating the area of a location to the depth and frequency of a rainfall event for a certain temporal duration and return period. The calculation of the ADDF curves is, however, not straightforward, as, in contrast to point precipitation, areal precipitation is not measured but must be estimated. This work considers precipitation as a spatial phenomenon, without purely point statistics, and aims to assess areal precipitation extremes for the present and future time periods along their expected change with climate change.