Performance of flood frequency pooling analysis in a low CV context

Das, Samiran; Cunnane, C.

doi:10.1080/02626667.2012.666635

Cited by 19 publications

(14 citation statements)

References 20 publications

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“…larger box) when N ≤ 10. In this regard, Das and Cunnane (2012) also found an effect for N < 10 on quantile error measures (considering n = 35). In general this effect is less marked for GI when γ = 0 % ( Fig.…”

Section: Sensitivity Analysesmentioning

confidence: 88%

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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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Section: Sensitivity Analysesmentioning

confidence: 88%

“…In the present study, heterogeneous regions are simulated using the heterogeneity rate γ , defined as γ = (max i (τ i ) − min i (τ i ))/τ R (e.g. Hosking and Wallis, 1997;Das and Cunnane, 2012), where τ i is the L-CV at site i with i = 1, . .…”

Section: Synthetic Regionsmentioning

confidence: 99%

Heterogeneity measures in hydrological frequency analysis: review and new developments

Requena

Chebana

Ouarda

2017

Hydrol. Earth Syst. Sci.

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“…Obviously, the quantiles estimated by RFA have smaller uncertainty than at-site based estimates as confirmed in Tables 13 and 14. However, there is a limitation of how large the return period could reliably be estimated with respect to record length. Das and Cunnane (2012) suggested that the record length of the considered site should be at least 50 years to estimate 100-year return period quantiles effectively. We assume loosely that this statement implies the factor of 2 between the record length and return period.…”

Section: Comparison Of At-site Quantile Uncertainty Between 2 Approacmentioning

confidence: 99%

“…The reliable estimation of such extreme rainfall events requires at-site long records. Das and Cunnane (2012) showed that for at-site frequency analysis, the record length at the site concerned should exceed 50 years for the estimation of 100-year flood. However, in many regions of the world, Jakarta inclusive, the scarcity and uncertainty of data remain challenged.…”

Section: Introductionmentioning

confidence: 99%

Regional frequency analysis of extreme rainfall events in Jakarta

et al. 2014

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Jakarta is vulnerable to flooding and extreme rainfall events are always the main cause of the occurrence of heavy flood events with loss of life and property. The flood in February 2007 is one of the most devastating events with the total rainfall during the 2-week period amounted to almost one-fourth of the total rainfall in 2007 at some stations. The huge scale of the loss due to this event as well as a series of big consecutive events the following years draw the attention to understand the flood risk in detail for Jakarta region. The study aimed to (1) estimate the return period for the February 2007 event in Jakarta, (2) develop intensity-duration-frequency (IDF) curves as well as the corresponding confidence intervals for Jakarta region up to 7-day duration and (3) understand the uncertainty of developed IDF curves induced with at-site and regional approaches. Daily rainfall data from 11 stations within Jakarta region with record lengths ranging from 15 to 22 years were collected. As the reliability of the frequency analysis is influenced by record length available, the frequencies and magnitudes of extreme rainfall events in the Jakarta region were analyzed by regional frequency analysis (RFA) based on the method of L-moments. One station (Darmaga) was removed from 11 stations after the data quality and homogenization check. The annual maximum rainfall series of duration of 1, 2, 3, 4, 5, 6, and 7 day at the 10 stations in Jakarta were then aggregated for the investigation. Because the value of discordancy measure exceeded the critical value, station Tangerang was subsequently removed from the group. Annual maximum series at these 9 stations were finally combined as the study region and passed the discordancy measure and heterogeneity measures of RFA. The accuracy of at-site rainfall quantile estimates by at-site and RFA was assessed and compared by error bounds at the confidence level of 90 %, based on Monte Carlo simulations by fitting generalized extreme value probability distributions to the regional average sample L-moment ratios. The results showed that the return period of event in Jakarta is over 300 year for 3-day duration at Halim station; close to 200 and 150-year return periods for 7-day duration at Halim and Pdk Betung stations, respectively. For the first time, the Jakarta regional multi-day IDF curves together with the corresponding 90 % confidence intervals for 2, 5, 10, 30, 50, 100, 200, and 300 year were developed. For effective flood risk mapping/mitigation in Jakarta, duration of longer than 1-day design storm should be considered. Also frequent re-visit of the IDF curves is indeed important if severe storms occurred after the IDF curves are established. Finally, the study suggested that more stations/data should be acquired for the region so that the estimation is more robust and reliable.Keywords L-moments Á Regional frequency analysis Á Rainfall extremes Á Multi-day intensity-duration-frequency Á Error bound Á Jakarta flood List of symbols T Return period, annual recurrence interv...

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“…If homogeneity is assured then a homogeneous region (or pooling group) of stations lead to a reduction in the error of quantile estimates, relative to estimators based on single at‐site data series alone (e.g. Hosking and Wallis, ; Das and Cunnane, ).…”

Section: Introductionmentioning

confidence: 99%

Performance of region‐of‐influence approach of frequency analysis of extreme rainfall in monsoon climate conditions

Das

2017

Intl Journal of Climatology

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This study investigates the applicability of the region‐of‐influence (ROI) approach of frequency analysis of extreme rainfall in a monsoon‐dominated country and to find the most appropriate scheme of the method. Seven different ROI pooling schemes are examined which differ in their similarly distance measure containing a range of different site descriptors (also known as pooling variables). The site descriptors also include average annual monsoon rainfall (AAMR) which is introduced to assess its suitability in this climatic condition. The ROI schemes are evaluated against traditional regional as well as at‐site frequency analysis. The performance of the selected scheme in terms of homogeneity and frequency behaviour is also assessed. In order to determine the performance, the study uses annual maximum rainfall data of 1‐day duration at 34 stations in Bangladesh, which has a tropical monsoon climate. It is found that the ROI method of any variants is superior to the traditional geographical approach of regional analysis as well as to the at‐site analysis. The AAMR based pooling scheme has provided the best result among the considered ROI schemes. The pooling groups delineated based on AAMR has also passed the homogeneity test and conveyed a desirable frequency behaviour. All results indicate that the AAMR as a pooling variable, i.e. information about monsoon rainfall, should be accommodated to the estimation of extreme rainfall in a monsoon‐dominated region.

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Performance of flood frequency pooling analysis in a low CV context

Cited by 19 publications

References 20 publications

Heterogeneity measures in hydrological frequency analysis: review and new developments

Heterogeneity measures in hydrological frequency analysis: review and new developments

Regional frequency analysis of extreme rainfall events in Jakarta

Performance of region‐of‐influence approach of frequency analysis of extreme rainfall in monsoon climate conditions

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