A rainfall threshold-based approach to early warnings in urban data-scarce regions

A rainfall threshold-based approach to early warnings in urban data-scarce regions: A case study of pluvial flooding in Alexandria, Egypt

Young, A.T. (TU Delft Hydraulic Structures and Flood Risk; IHE Delft Institute for Water Education)
Bhattacharya, Biswa (IHE Delft Institute for Water Education)
Zevenbergen, C. (TU Delft Hydraulic Structures and Flood Risk; IHE Delft Institute for Water Education)

2021

Rapidly expanding cities in the Middle Eastern and North African (MENA) region are at risk of flooding due to heavy rainfall, insufficient drainage capacity, a lack of preparedness and insufficient data to conduct required studies. A low regret Early Warning Systems (EWS) using rainfall thresholds is proposed as a cost-effective short-term solution. This study aims to utilise a probabilistic approach to characterise and predict urban floods by assessing critical rainfall thresholds likely to cause flooding combined with ensemble precipitation forecast in Alexandria, Egypt. Rainfall thresholds were inferred by associating observed rainfall and historical flood information sourced from social media and newspapers. Floods were classified in a colour-coded hazard matrix as no flood (green), minor flood (yellow), significant flood (orange), and severe flood (red). Probability of occurrence of hazard classes was derived by incorporating ensemble rainfall into the hazard matrix to jointly evaluate likelihood and hazard severity. Results from this study showed that three of four severe events analysed could have been predicted with a high likelihood up to 24 hr before. The presented approach supports decision making to issue warnings and flood control actions with limited data and is a model for other data scare regions.

early warning systems
Egypt
pluvial flood forecasting
rainfall thresholds

http://resolver.tudelft.nl/uuid:c1b952c5-066c-4c0f-bf14-88784de2ad50

https://doi.org/10.1111/jfr3.12702

1753-318X

Journal of Flood Risk Management, 14 (2), 1-16

Institutional Repository

journal article

© 2021 A.T. Young, Biswa Bhattacharya, C. Zevenbergen