Advances and challenges in flash flood warnings

The runoff from heavy rainfall reaches urban streams quickly, causing them to rise rapidly. It is therefore of great importance to provide sufficient lead time for evacuation planning and decision making. An efficient flood forecasting and warning method is crucial for ensuring adequate lead time. With this objective, this paper proposes an analysis method for a flood forecasting and warning system, and establishes the criteria for issuing urban-stream flash flood warnings based on the amount of rainfall to allow sufficient lead time. The proposed methodology is a nonstructural approach to flood prediction and risk reduction. It considers water level fluctuations during a rainfall event and estimates the upstream (alert point) and downstream (confluence) water levels for water level analysis based on the rainfall intensity and duration. We also investigate the rainfall/runoff and flow rate/water level relationships using the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) and the HEC’s River Analysis System (HEC-RAS) models, respectively, and estimate the rainfall threshold for issuing flash flood warnings depending on the backwater state based on actual watershed conditions. We present a methodology for issuing flash flood warnings at a critical point by considering the effects of fluctuations in various backwater conditions in real time, which will provide practical support for decision making by disaster protection workers. The results are compared with real-time water level observations of the Dorim Stream. Finally, we verify the validity of the flash flood warning criteria by comparing the predicted values with the observed values and performing validity analysis.

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Establishing a rainfall threshold for flash flood warnings in China’s mountainous areas based on a distributed hydrological model

Journal of Hydrology ◽

10.1016/j.jhydrol.2016.04.054 ◽

2016 ◽

Vol 541 ◽

pp. 371-386 ◽

Cited By ~ 46

Author(s):

Qinghua Miao ◽

Dawen Yang ◽

Hanbo Yang ◽

Zhe Li

Keyword(s):

Hydrological Model ◽

Flash Flood ◽

Rainfall Threshold ◽

Distributed Hydrological Model ◽

Mountainous Areas ◽

Flood Warnings

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A Data-Driven Probabilistic Rainfall-Inundation Model for Flash-Flood Warnings

Water ◽

10.3390/w11122534 ◽

2019 ◽

Vol 11 (12) ◽

pp. 2534 ◽

Cited By ~ 2

Author(s):

Tsung-Yi Pan ◽

Hsuan-Tien Lin ◽

Hao-Yu Liao

Keyword(s):

Pattern Analysis ◽

Flash Flood ◽

Numerical Models ◽

Training Data ◽

Rainfall Pattern ◽

Data Driven ◽

Support Vector ◽

Threshold Method ◽

Inundation Model ◽

Flood Warnings

Owing to their short duration and high intensity, flash floods are among the most devastating natural disasters in metropolises. The existing warning tools—flood potential maps and two-dimensional numerical models—are disadvantaged by time-consuming computation and complex model calibration. This study develops a data-driven, probabilistic rainfall-inundation model for flash-flood warnings. Applying a modified support vector machine (SVM) to limited flood information, the model provides probabilistic outputs, which are superior to the Boolean functions of the traditional rainfall-flood threshold method. The probabilistic SVM-based model is based on a data preprocessing framework that identifies the expected durations of hazardous rainfalls via rainfall pattern analysis, ensuring satisfactory training data, and optimal rainfall thresholds for validating the input/output data. The proposed model was implemented in 12 flash-flooded districts of the Xindian River. It was found that (1) hydrological rainfall pattern analysis improves the hazardous event identification (used for configuring the input layer of the SVM); (2) brief hazardous events are more critical than longer-lasting events; and (3) the SVM model exports the probability of flash flooding 1 to 3 h in advance.

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Comments on “Flash Flood Verification: Pondering Precipitation Proxies”

Journal of Hydrometeorology ◽

10.1175/jhm-d-20-0215.1 ◽

2021 ◽

Vol 22 (3) ◽

pp. 739-747

Author(s):

Jonathan J. Gourley ◽

Humberto Vergara

Keyword(s):

Flash Flood ◽

End Users ◽

Next Generation ◽

Dual Polarization ◽

Flash Flooding ◽

Radar Network ◽

Operational Forecasting ◽

Precipitation Estimates ◽

Quantitative Precipitation Estimates ◽

Flood Warnings

AbstractNew operational tools for monitoring flash flooding based on radar quantitative precipitation estimates (QPEs) have become available to U.S. National Weather Service forecasters. Herman and Schumacher examined QPE exceedance thresholds for several tools and compared them to each other, to flash flood reports (FFRs), and to flash flood warnings. The Next Generation Radar network has been updated with dual-polarization capabilities since the publication of Herman and Schumacher, which has changed the characteristics of the derived QPEs. Updated thresholds on Multi-Radar Multi-Sensor version 12 products that are associated to FFRs are provided and thus can be used as guidance by the operational forecasting community and other end-users of the products.

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Risk Perception, Risk Communication, and Mitigation Actions of Flash Floods: Results from a Survey in Three Types of Communities

Sustainability ◽

10.3390/su132212389 ◽

2021 ◽

Vol 13 (22) ◽

pp. 12389

Author(s):

Ming Zhong ◽

Lu Xiao ◽

Qian Zhang ◽

Tao Jiang

Keyword(s):

Risk Perception ◽

Risk Communication ◽

Rural Community ◽

Risk Perceptions ◽

Flash Flood ◽

Protective Action ◽

Community Resilience ◽

Flash Floods ◽

Flood Hazards ◽

Flood Warnings

In order to improve the decision-making of risk management and enhance community resilience to flash floods, the perception of risks, communication of warnings, and mitigation actions concerning flash floods were investigated in this study. The survey involves 280 participants from three types of communities in flash flood-prone areas. Results show that: (i) About 55.4% of community participants misperceived or underestimated the risk of flash floods, especially in the suburban communities, and people had misconceptions about the safety of crossing fast-flowing water, even though most of them had experienced flash flood hazards. (ii) In total, 67.9% of participants indicated that they had at some point received a flash flood warning. The perception of accuracy was related to trust in flash flood warnings, but they were different constructs for some individuals. Moreover, residents in the rural community and suburban community reported a closer social communication with neighbors, which would greatly influence inhabitants’ attitudes and behaviors towards the flash flood warnings and mitigation actions. (iii) Most of the participants indicated they would take some protective action when they received a warning. Risk perceptions and risk communications influence the mitigation actions in the community. Significant variables in the rural community and non-rural community were explored, and some important suggestions are highlighted. These findings suggest that risk perception and risk communication in neighborhoods help people to decide what action to take in the given scenarios, contribute to enhancing the community resilience, and contribute to coping with future flash floods in a more specific and effective way.

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