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<p>Urban flooding represents a growing challenge in arid cities due to the increasing frequency of extreme rainfall events associated with climate change and rapid urbanization. In Jeddah, Saudi Arabia, flash floods pose significant risks to infrastructure and public safety, particularly in the downstream area of Wadi Qows, where extensive impervious surfaces and limited natural drainage exacerbate flood hazards. This study aims to support urban resilience by mapping and assessing flood risk in this arid urban environment. Flood hazard assessment was conducted by integrating field observations, Geographic Information Systems (GIS), hydrological modeling, and 2D hydraulic modeling. Flood inundation depths were simulated using the HEC-RAS 2D model and validated against observed data from the major flood event of November 25, 2009. Design storms corresponding to return periods of 5, 10, 25, 50, 100, and 200 years were analyzed, and a Flood Risk Matrix was applied to classify spatial flood risk levels. The simulated flood depths by HEC RAS model were generally consistent with the field measurements, as reflected by a correlation coefficient of <i>r</i> = 0.79, an RMSE of 0.43&#xa0;m, and an NSE of 0.63, which indicate satisfactory model performance. Flood risk mapping revealed an expansion of high- and very-high-risk zones with increasing return periods, particularly in densely urbanized downstream areas. The results provide a practical, risk-based framework for flood mitigation and urban resilience planning in arid cities and offer valuable guidance for decision-makers and emergency management authorities.</p> Graphical Abstract <p>In this study, a framework for flood risk assessment is presented for the downstream area of Wadi Qows in Jeddah, Saudi Arabia. To simulate flood scenarios for return periods of 5–200 years, field data, GIS, hydrological (HEC-HMS) and hydraulic (2D HEC-RAS) models were combined. Validation of the model using the November 25, 2009 event revealed good agreement (R2 = 0.79, RMSE = 0.42 m). With increasing return periods, flood depths and extents increase. In order to classify risk levels from low to very high and identify critical zones, a Flood Risk Matrix (FRM) was used. For flood management in arid urban environments, the framework supports decision-making, land-use planning, infrastructure design, and disaster risk reduction.</p>

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Mapping and Assessment of Flood Risk in an Urban Arid Environment: Wadi Qows Downstream Area, Jeddah City, Saudi Arabia

  • 期刊论文

  • 发表日期：

    2026年6月15日

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  • Mohamed Hafedh Hamza,
  • Anis Chaabani,
  • Amro Elfeki,
  • Nuaman Ejaz,
  • Adélia Nunes,
  • Aris Pislovikos,
  • Wei Tian,
  • Sanju Purohit,
  • Mohamed Elhag

摘要

Urban flooding represents a growing challenge in arid cities due to the increasing frequency of extreme rainfall events associated with climate change and rapid urbanization. In Jeddah, Saudi Arabia, flash floods pose significant risks to infrastructure and public safety, particularly in the downstream area of Wadi Qows, where extensive impervious surfaces and limited natural drainage exacerbate flood hazards. This study aims to support urban resilience by mapping and assessing flood risk in this arid urban environment. Flood hazard assessment was conducted by integrating field observations, Geographic Information Systems (GIS), hydrological modeling, and 2D hydraulic modeling. Flood inundation depths were simulated using the HEC-RAS 2D model and validated against observed data from the major flood event of November 25, 2009. Design storms corresponding to return periods of 5, 10, 25, 50, 100, and 200 years were analyzed, and a Flood Risk Matrix was applied to classify spatial flood risk levels. The simulated flood depths by HEC RAS model were generally consistent with the field measurements, as reflected by a correlation coefficient of r = 0.79, an RMSE of 0.43 m, and an NSE of 0.63, which indicate satisfactory model performance. Flood risk mapping revealed an expansion of high- and very-high-risk zones with increasing return periods, particularly in densely urbanized downstream areas. The results provide a practical, risk-based framework for flood mitigation and urban resilience planning in arid cities and offer valuable guidance for decision-makers and emergency management authorities.

Graphical Abstract

In this study, a framework for flood risk assessment is presented for the downstream area of Wadi Qows in Jeddah, Saudi Arabia. To simulate flood scenarios for return periods of 5–200 years, field data, GIS, hydrological (HEC-HMS) and hydraulic (2D HEC-RAS) models were combined. Validation of the model using the November 25, 2009 event revealed good agreement (R2 = 0.79, RMSE = 0.42 m). With increasing return periods, flood depths and extents increase. In order to classify risk levels from low to very high and identify critical zones, a Flood Risk Matrix (FRM) was used. For flood management in arid urban environments, the framework supports decision-making, land-use planning, infrastructure design, and disaster risk reduction.