Showing papers by "Thomas Kjeldsen published in 2021"
TL;DR: A number of extraordinary flood events occurred recently in northwest England, with several severe floods in Cumbria, Lancashire and the Manchester area in 2004, 2009 and 2015 as discussed by the authors.
Abstract: Extraordinary flood events occurred recently in northwest England, with several severe floods in Cumbria, Lancashire and the Manchester area in 2004, 2009 and 2015. These clustered extraordinary ev...
20 citations
TL;DR: In this article, a change-permitting model for quantile estimates is proposed, which is based on the Generalized Extreme Value (GEV) distribution and assumes a constant coefficient of variation, allowing the location and scale parameters to change simultaneously.
Abstract: The potential for changes in environmental extremes is routinely investigated by fitting change-permitting extreme value models to long-term observations, allowing one or more distribution parameters to change as a function of time or some other covariate. In most extreme value analyses, the main quantity of interest is typically the upper quantiles of the distribution, which are often needed for practical applications such as engineering design. This study focuses on the changes in quantile estimates under different change-permitting models. First, metrics which measure the impact of changes in parameters on changes in quantiles are introduced. The mathematical structure of these change metrics is investigated for several change-permitting models based on the Generalised Extreme Value (GEV) distribution. It is shown that for the most commonly used models, the predicted changes in the quantiles are a non-intuitive function of the distribution parameters, leading to results which are difficult to interpret. Next, it is posited that commonly used change-permitting GEV models do not preserve a constant coefficient of variation, a property that is typically assumed to hold for environmental extremes. To address these shortcomings a new (parsimonious) model is proposed: the model assumes a constant coefficient of variation, allowing the location and scale parameters to change simultaneously. The proposed model results in changes in the quantile function that are easier to interpret. Finally, the consequences of the different modelling choices on quantile estimates are exemplified using a dataset of extreme peak river flow measurements in Massachusetts, USA. It is argued that the decision on which model structure to adopt to describe change in extremes should also take into consideration any requirements on the behaviour of the quantiles of interest.
12 citations
4 citations
2 citations
TL;DR: In this paper, the authors proposed a new method for estimating a regional regression slope parameter across a region, or pooling group, of catchment considered hydrologically similar, and where annual maximum events at different sites are cross-correlated.
2 citations
11 Oct 2021
TL;DR: In this article, an easy-to-use equation for calculating the variance of a design flood estimated using a generalised logistic distribution with model parameters estimated using single-site analysis is presented.
Abstract: An easy-to-use equation is presented for calculating the variance of a design flood estimated using a generalised logistic distribution with model parameters estimated using single-site analysis, a...