Design Flood Estimation Methods for Cascade Reservoirs Based on Copulas

Research into potential implications of climate change on flood hazard has made significant progress over the past decade, yet efforts to translate this research into practical guidance for flood estimation remain in their infancy. In this commentary, we address the question: how best can practical flood guidance be modified to incorporate the additional uncertainty due to climate change? We begin by summarizing the physical causes of changes in flooding and then discuss common methods of design flood estimation in the context of uncertainty. We find that although climate science operates across aleatory, epistemic and deep uncertainty, engineering practitioners generally only address aleatory uncertainty associated with natural variability through standards-based approaches. A review of existing literature and flood guidance reveals that although research efforts in hydrology do not always reflect the methods used in flood estimation, significant progress has been made with many jurisdictions around the world now incorporating climate change in their flood guidance. We conclude that the deep uncertainty that climate change brings signals a need to shift towards more flexible design and planning approaches, and future research effort should focus on providing information that supports the range of flood estimation methods used in practice. This article is part of a discussion meeting issue ‘Intensification of short-duration rainfall extremes and implications for flash flood risks'.

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Nonstationary Design Flood Estimation in Response to Climate Change, Population Growth and Cascade Reservoir Regulation

Water ◽

10.3390/w13192687 ◽

2021 ◽

Vol 13 (19) ◽

pp. 2687

Author(s):

Yuzuo Xie ◽

Shenglian Guo ◽

Lihua Xiong ◽

Jing Tian ◽

Feng Xiong

Keyword(s):

Climate Change ◽

Population Growth ◽

Change Point Detection ◽

Flood Frequency Analysis ◽

Data Series ◽

Flood Events ◽

Design Flood ◽

Cascade Reservoirs ◽

Han River ◽

Flood Estimation

The hydrologic data series are nonstationary due to climate change and local anthropogenic activities. The existing nonstationary design flood estimation methods usually focus on the statistical nonstationarity of the flow data series in the catchment, which neglect the hydraulic approach, such as reservoir flood regulation. In this paper, a novel approach to comprehensively consider the driving factors of non-stationarities in design flood estimation is proposed, which involves three main steps: (1) implementation of the candidate predictors with trend tests and change point detection for preliminary analysis; (2) application of the nonstationary flood frequency analysis with the principle of Equivalent Reliability (ER) for design flood volumes; (3) development of a nonstationary most likely regional composition (NS-MLRC) method, and the estimation of a design flood hydrograph at downstream cascade reservoirs. The proposed framework is applied to the cascade reservoirs in the Han River, China. The results imply that: (1) the NS-MLRC method provides a much better explanation for the nonstationary spatial correlation of the flood events in Han River basin, and the multiple nonstationary driving forces can be precisely quantified by the proposed design flood estimation framework; (2) the impacts of climate change and population growth are long-lasting processes with significant risk of flood events compared with stationary distribution conditions; and (3) the swift effects of cascade reservoirs are reflected in design flood hydrographs with lower peaks and lesser volumes. This study can provide a more integrated template for downstream flood risk management under the impact of climate change and human activities.

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Assessment of at‐site design flood estimation methods using an improved event‐based design flood estimation tool

Journal of Flood Risk Management ◽

10.1111/jfr3.12710 ◽

2021 ◽

Author(s):

Ockert Jacobus Gericke

Keyword(s):

Estimation Methods ◽

Design Flood ◽

Flood Estimation ◽

Site Design ◽

Event Based

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The influence of soil moisture conditions on the spatio-temporal variability of event rainfall-runoff coefficients in UK catchments

10.5194/egusphere-egu21-6047 ◽

2021 ◽

Author(s):

Yanchen Zheng ◽

Ross Woods ◽

Jianzhu Li ◽

Ping Feng

Keyword(s):

Soil Moisture ◽

Temporal Variability ◽

Estimation Methods ◽

Runoff Coefficient ◽

Rainfall Runoff ◽

Design Flood ◽

Ungauged Catchments ◽

Flood Estimation ◽

Spatio Temporal ◽

Moisture Conditions

<p>Since the bias and uncertainties of the current design flood estimation methods for ungauged catchments are inevitable, estimation of the design flood in ungauged catchments still remains an unsolved problem. The derived distribution approach appears to be the one of the promising design flood estimation methods, as this method can improve the understanding on which processes contribute most to flood in ungauged catchments. Generally, the distribution of rainfall characteristics and lumped rainfall-runoff modelling was incorporated to estimate the flood magnitude in this method. However, we should note that rainfall is not the only driving factor of flood events. Soil moisture conditions are also an important driving factor affecting the rainfall-runoff transformation, and may even control rainfall-runoff coefficients to a higher degree than does rainfall. Hence, here we perform soil moisture analysis at national scale by employing GLDAS-Noah datasets, and link this to observed event runoff coefficients from a large sample of UK catchments. The relationship between soil moisture conditions and rainfall-runoff coefficient was explored to analyse the spatio-temporal variability of runoff coefficient. This study laid the foundation for further development of a practical derived distribution method, by considering the statistical distribution of rainfall-runoff coefficients and the influence of soil moisture conditions.</p>

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