Regional flood frequency analysis at the global scale

Smith, Andrew M.; Sampson, Chris; Bates, Paul

doi:10.1002/2014wr015814

Cited by 157 publications

(174 citation statements)

References 58 publications

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“…Linear or power (often linearised through a log-transformation) forms, with either a multiplicative or additive error term, are the most commonly used functions (see e.g. Stedinger and Tasker, 1985;GRE-HYS, 1996;Pandey and Nguyen, 1999;Brath et al, 2001;Kjeldsen et al, 2001Kjeldsen et al, , 2014Bocchiola et al, 2003;Merz and Bloeschl, 2005;Griffis and Stedinger, 2007;Archfield et al, 2013;Smith et al, 2015).…”

Section: E Toth: Estimation Of Flood Warning Runoff Thresholds In Unmentioning

confidence: 99%

Estimation of flood warning runoff thresholds in ungauged basins with asymmetric error functions

Toth

2016

Hydrol. Earth Syst. Sci.

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Abstract. In many real-world flood forecasting systems, the runoff thresholds for activating warnings or mitigation measures correspond to the flow peaks with a given return period (often 2 years, which may be associated with the bankfull discharge). At locations where the historical streamflow records are absent or very limited, the threshold can be estimated with regionally derived empirical relationships between catchment descriptors and the desired flood quantile. Whatever the function form, such models are generally parameterised by minimising the mean square error, which assigns equal importance to overprediction or underprediction errors.Considering that the consequences of an overestimated warning threshold (leading to the risk of missing alarms) generally have a much lower level of acceptance than those of an underestimated threshold (leading to the issuance of false alarms), the present work proposes to parameterise the regression model through an asymmetric error function, which penalises the overpredictions more.The estimates by models (feedforward neural networks) with increasing degree of asymmetry are compared with those of a traditional, symmetrically trained network, in a rigorous cross-validation experiment referred to a database of catchments covering the country of Italy. The analysis shows that the use of the asymmetric error function can substantially reduce the number and extent of overestimation errors, if compared to the use of the traditional square errors. Of course such reduction is at the expense of increasing underestimation errors, but the overall accurateness is still acceptable and the results illustrate the potential value of choosing an asymmetric error function when the consequences of missed alarms are more severe than those of false alarms.

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Section: E Toth: Estimation Of Flood Warning Runoff Thresholds In Unmentioning

confidence: 99%

Estimation of flood warning runoff thresholds in ungauged basins with asymmetric error functions

Toth

2016

Hydrol. Earth Syst. Sci.

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“…Smith et al [2] performed a regional flood frequency analysis (RFFA) at global scale using 703 discharge gauges from the Global Runoff Data Centre (GRDC) and a global annual average rainfall dataset from World-Clim [3]. Regressions were used to calculate the mean annual flood and they concluded that the best regressions used just catchment area and annual average rainfall as estimators.…”

Section: Introductionmentioning

confidence: 99%

Pluvial Flooding in European Cities—A Continental Approach to Urban Flood Modelling

Guerreiro

Glenis

Dawson

et al. 2017

Water

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Pluvial flooding is caused by localized intense rainfall and the flood models used to assess it are normally applied on a city (or part of a city) scale using local rainfall records and a high resolution digital elevation model (DEM). Here, we attempt to model pluvial flooding on a continental scale and calculate the percentage of area flooded for all European cities for a 10-year return period for hourly rainfall (RP10). Difficulties in obtaining hourly rainfall records compromise the estimation of each city RP10 and the Europe-wide DEM spatial resolution is low relative to those typically used for individual case-studies. Nevertheless, the modelling capabilities and necessary computing power make this type of continental study now possible. This is a first attempt at continental city flooding modelling and our methodology was designed so that our results can easily be updated as better/more data becomes available. The results for each city depend on the interplay of rainfall intensity, the elevation map of the city and the flow paths that are created. In general, cities with lower percentage of city flooded are in the north and west coastal areas of Europe, while the higher percentages are seen in continental and Mediterranean areas.

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“…In this test the statistic H is related to the variability of the at-site L-variation coefficient (L-CV) over a region (e.g. Alila, 1999;Burn and Goel, 2000;Castellarin et al, 2001;Shu and Burn, 2004;Smith et al, 2015;Ouarda, 2016).…”

Section: Introductionmentioning

confidence: 99%

Heterogeneity measures in hydrological frequency analysis: review and new developments

Requena

Chebana

Ouarda

2017

Hydrol. Earth Syst. Sci.

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Abstract. Some regional procedures to estimate hydrological quantiles at ungauged sites, such as the index-flood method, require the delineation of homogeneous regions as a basic step for their application. The homogeneity of these delineated regions is usually tested providing a yes/no decision. However, complementary measures that are able to quantify the degree of heterogeneity of a region are needed to compare regions, evaluate the impact of particular sites, and rank the performance of different delineating methods. Well-known existing heterogeneity measures are not welldefined for ranking regions, as they entail drawbacks such as assuming a given probability distribution, providing negative values and being affected by the region size. Therefore, a framework for defining and assessing desirable properties of a heterogeneity measure in the regional hydrological context is needed. In the present study, such a framework is proposed through a four-step procedure based on Monte Carlo simulations. Several heterogeneity measures, some of which commonly known and others which are derived from recent approaches or adapted from other fields, are presented and developed to be assessed. The assumption-free Gini index applied on the at-site L-variation coefficient (L-CV) over a region led to the best results. The measure of the percentage of sites for which the regional L-CV is outside the confidence interval of the at-site L-CV is also found to be relevant, as it leads to more stable results regardless of the regional L-CV value. An illustrative application is also presented for didactical purposes, through which the subjectivity of commonly used criteria to assess the performance of different delineation methods is underlined.

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Regional flood frequency analysis at the global scale

Cited by 157 publications

References 58 publications

Estimation of flood warning runoff thresholds in ungauged basins with asymmetric error functions

Estimation of flood warning runoff thresholds in ungauged basins with asymmetric error functions

Pluvial Flooding in European Cities—A Continental Approach to Urban Flood Modelling

Heterogeneity measures in hydrological frequency analysis: review and new developments

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