Making Room for the Wadi: A Review of Urban Flash-Flood Resilience and Water-Sensitive Design in Saudi Cities, with a Layered Framework for Flood-Resilient Public Space

Flash floods are rare in Saudi cities, but when they come they are fast, deep and deadly. The Jeddah floods of November 2009 and January 2011 killed more than a hundred people, and the storm of 24 November 2022 delivered 179.7 mm of rain in about eight hours, the highest total ever recorded in the city. This review brings together peer-reviewed and official evidence on urban flash-flood risk in western Saudi Arabia, with Jeddah and the Makkah region as the main case and Riyadh as a comparison. It covers the documented flood events and rainfall regime, hydrological and GIS studies of the urban wadis, the growth of the cities into their floodplains, the engineering response of dams, channels and forecasting, and the evidence on water-sensitive urban design (WSUD), sustainable drainage and nature-based solutions in arid regions, including the restoration of Wadi Hanifah in Riyadh. The evidence shows a consistent pattern. Floods follow old wadi courses that were filled, built over or cut by roads, and the response has relied mainly on single-purpose grey infrastructure. Arid-region studies show that green and multifunctional measures can reduce runoff, but local performance data are scarce. Building on this synthesis, the paper proposes the Wadi-to-Plot (W2P) framework. It links four nested scales (catchment, district, street and plot) through a network of multifunctional public spaces, such as floodable wadi parks, sunken plazas and conveyance streets, that serve daily life in dry weather and store or route water during storms. Each scale carries measurable indicators for design review and monitoring. The paper ends with a research agenda for Saudi practice.