TY - JOUR A1 - Macdonald, Elena A1 - Otero, Noelia A1 - Butler, Tim T1 - A comparison of long-term trends in observations and emission inventories of NOx JF - Atmospheric chemistry and physics / European Geosciences Union N2 - Air pollution is a pressing issue that is associated with adverse effects on human health, ecosystems, and climate. Despite many years of effort to improve air quality, nitrogen dioxide (NO2) limit values are still regularly exceeded in Europe, particularly in cities and along streets. This study explores how concentrations of nitrogen oxides (NOx = NO + NO2) in European urban areas have changed over the last decades and how this relates to changes in emissions. To do so, the incremental approach was used, comparing urban increments (i.e. urban background minus rural concentrations) to total emissions, and roadside increments (i.e. urban roadside concentrations minus urban background concentrations) to traffic emissions. In total, nine European cities were assessed. The study revealed that potentially confounding factors like the impact of urban pollution at rural monitoring sites through atmospheric transport are generally negligible for NOx. The approach proves therefore particularly useful for this pollutant. The estimated urban increments all showed downward trends, and for the majority of the cities the trends aligned well with the total emissions. However, it was found that factors like a very densely populated surrounding or local emission sources in the rural area such as shipping traffic on inland waterways restrict the application of the approach for some cities. The roadside increments showed an overall very diverse picture in their absolute values and trends and also in their relation to traffic emissions. This variability and the discrepancies between roadside increments and emissions could be attributed to a combination of local influencing factors at the street level and different aspects introducing inaccuracies to the trends of the emis-sion inventories used, including deficient emission factors. Applying the incremental approach was evaluated as useful for long-term pan-European studies, but at the same time it was found to be restricted to certain regions and cities due to data availability issues. The results also highlight that using emission inventories for the prediction of future health impacts and compliance with limit values needs to consider the distinct variability in the concentrations not only across but also within cities. Y1 - 2021 U6 - https://doi.org/10.5194/acp-21-4007-2021 SN - 1680-7316 SN - 1680-7324 VL - 21 IS - 5 SP - 4007 EP - 4023 PB - Copernicus CY - Göttingen ER - TY - THES A1 - Macdonald, Elena T1 - Stable isotopes in precipitation: Modelling intra-event variations using meteorological parameters T1 - Stabile Isotope im Niederschlag: Modellierung von Ereignis-internen Variationen mit meteorologischen Parametern N2 - Die kurzfristige Variabilität der Isotopenzusammensetzung von Niederschlägen in Golm, Deutschland wurde untersucht und modelliert. Dafür wurden Isotopendaten (D/H und 18O/16O) mit einer hohen zeitlichen Auflösung sowie meteorologische Daten von einer Wetterstation und einem Mikroregenradar genutzt. Nach der Datenaufbereitung und dem Zusammenführen aller drei Datensätze wurde eine multivariate lineare Regressionsanalyse durchgeführt. Dies geschah für vier verschiedene, auf den Isotopendaten beruhende Response-Variablen und für den gesamten Datensatz sowie für die zwei Teildatensätze Sommer und Winter. Die verwendeten Response-Variablen sind die Differenzen der δ18O-Werte zu den ereignisbasierten Mittel- und Medianwerten und die Differenzen der Deuterium-Exzess-Werte zu den ereignisbasierten Mittel- und Medianwerten. Für die erhaltenen Modelle wurden die modellierten Werte mit den gemessenen Werten verglichen, wobei sich herausstellte, dass die Messwerte nicht zufriedenstellend wiedergegeben werden konnten. Daher werden am Ende mehrere Vorschläge gemacht, wie das Vorgehen und damit auch das Ergebnis der Modellierung möglicherweise verbessert werden kann. N2 - The short-term variability of the isotopic composition of precipitation in Golm, Germany was assessed and modelled. Isotopic data (D/H and 18O/16O) on intra-event timescales as well as meteorological data from a weather station and a micro rain radar was used. After data preparation and the combination of all three data sets, a multivariate linear regression analysis was conducted. This was done for four different isotopic response variables and for the entire data set as well as for the two subsets Summer and Winter. The used response variables are the δ18O values as the difference to the corresponding event-based mean and as the difference to the median, and the deuterium excess values as the difference to both the mean and the median. The models were evaluated by comparing the modelled values with the observed ones. This showed that the observations could not be reproduced in a satisfactory way. Therefore, several suggestions on how to possibly improve the methods and thus the modelling results are given in the end. KW - stable isotopes KW - isotopic composition KW - micro rain radar KW - multivariate linear regression model KW - stabile Isotope KW - Isotopenzusammensetzung KW - Mikroregenradar KW - multivariates lineares Regressionsmodell Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-506612 ER - TY - JOUR A1 - Merz, Bruno A1 - Basso, Stefano A1 - Fischer, Svenja A1 - Lun, David A1 - Bloeschl, Guenter A1 - Merz, Ralf A1 - Guse, Bjorn A1 - Viglione, Alberto A1 - Vorogushyn, Sergiy A1 - Macdonald, Elena A1 - Wietzke, Luzie A1 - Schumann, Andreas T1 - Understanding heavy tails of flood peak distributions JF - Water resources research N2 - Statistical distributions of flood peak discharge often show heavy tail behavior, that is, extreme floods are more likely to occur than would be predicted by commonly used distributions that have exponential asymptotic behavior. This heavy tail behavior may surprise flood managers and citizens, as human intuition tends to expect light tail behavior, and the heaviness of the tails is very difficult to predict, which may lead to unnecessarily high flood damage. Despite its high importance, the literature on the heavy tail behavior of flood distributions is rather fragmented. In this review, we provide a coherent overview of the processes causing heavy flood tails and the implications for science and practice. Specifically, we propose nine hypotheses on the mechanisms causing heavy tails in flood peak distributions related to processes in the atmosphere, the catchment, and the river system. We then discuss to which extent the current knowledge supports or contradicts these hypotheses. We also discuss the statistical conditions for the emergence of heavy tail behavior based on derived distribution theory and relate them to the hypotheses and flood generation mechanisms. We review the degree to which the heaviness of the tails can be predicted from process knowledge and data. Finally, we recommend further research toward testing the hypotheses and improving the prediction of heavy tails. KW - extreme events KW - flood frequency KW - flood risk KW - upper tail Y1 - 2022 U6 - https://doi.org/10.1029/2021WR030506 SN - 0043-1397 SN - 1944-7973 VL - 58 IS - 6 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Macdonald, Elena A1 - Merz, Bruno A1 - Guse, Björn A1 - Wietzke, Luzie A1 - Ullrich, Sophie A1 - Kemter, Matthias A1 - Ahrens, Bodo A1 - Vorogushyn, Sergiy T1 - Event and catchment controls of heavy tail behavior of floods JF - Water resources research N2 - In some catchments, the distribution of annual maximum streamflow shows heavy tail behavior, meaning the occurrence probability of extreme events is higher than if the upper tail decayed exponentially. Neglecting heavy tail behavior can lead to an underestimation of the likelihood of extreme floods and the associated risk. Partly contradictory results regarding the controls of heavy tail behavior exist in the literature and the knowledge is still very dispersed and limited. To better understand the drivers, we analyze the upper tail behavior and its controls for 480 catchments in Germany and Austria over a period of more than 50 years. The catchments span from quickly reacting mountain catchments to large lowland catchments, allowing for general conclusions. We compile a wide range of event and catchment characteristics and investigate their association with an indicator of the tail heaviness of flood distributions, namely the shape parameter of the GEV distribution. Following univariate analyses of these characteristics, along with an evaluation of different aggregations of event characteristics, multiple linear regression models, as well as random forests, are constructed. A novel slope indicator, which represents the relation between the return period of flood peaks and event characteristics, captures the controls of heavy tails best. Variables describing the catchment response are found to dominate the heavy tail behavior, followed by event precipitation, flood seasonality, and catchment size. The pre-event moisture state in a catchment has no relevant impact on the tail heaviness even though it does influence flood magnitudes. KW - heavy tail behavior KW - floods KW - event characteristics KW - catchment KW - characteristics KW - catchment response Y1 - 2022 U6 - https://doi.org/10.1029/2021WR031260 SN - 0043-1397 SN - 1944-7973 VL - 58 IS - 6 PB - American Geophysical Union CY - Washington ER -