Urban Flood Risk Generation under Climate-Incompatible Urban Development:An Integrated Analysis of the April 2026 Jahrom Flash Flood

Abstract

The April 2026 flash flood in Jahrom represents one of the most prominent examples of sudden flooding in Iran’s semi‑arid climate, where the interaction between short‑duration extreme rainfall, the hydrological characteristics of the watershed, climate‑incompatible urban development, and the weakness of urban infrastructure resulted in a widespread urban crisis. Despite numerous studies on urban flooding, the simultaneous role of hydrological processes, urban development, infrastructure failure, sediment transport, and urban resilience in generating flood risk, particularly in semi‑arid cities, has rarely been examined through an integrated framework. This study aims to explain the process of urban flood‑risk generation by analyzing, within a unified analytical framework, the behavior of the convective- urban runoff system, sub‑basin concentration time, flood‑entry pathways, the performance of urban infrastructure, the role of sediment transport and deposition, and the multiple dimensions of urban resilience, using field, documentary, hydrological, and infrastructural data.

The results indicate that rainfall intensity in 15‑ to 30‑minute intervals, combined with the very low permeability of clay–marl soils and sub‑basin concentration times of less than one hour, produced an extremely rapid hydrological response, activated southern ephemeral channels, and delivered substantial volumes of runoff into the urban area. Urban development within channel beds, channel narrowing, alteration of natural slopes, blockage of flow paths, and inappropriate placement of critical facilities significantly reduced the watershed’s natural capacity for storing, conveying, and routing runoff, causing even moderate‑intensity rainfall to result in extensive inundation. Furthermore, the failure of culverts, the transformation of bridges into hydraulic barriers, severe sediment deposition, and the absence of alternative flow routes revealed the role of urban infrastructure as a major driver of flood‑damage amplification.

The assessment of urban resilience showed that simultaneous weaknesses across physical, infrastructural, institutional, and social dimensions reduced the effectiveness of warning systems, inter‑sectoral coordination, and crisis management, limiting the city’s capacity for preparedness, response, and recovery. The findings demonstrate that flood risk in semi‑arid cities is not merely a consequence of extreme rainfall, but the product of interactions among climatic hazards, climate‑incompatible urban development, infrastructure dysfunction, sediment transport, and weak risk governance. Accordingly, the study presents an integrated framework for explaining the process of urban flood‑risk generation and proposes a set of policy strategies, including restoration of natural flow paths, redesign of the stormwater network, institutional reforms, climate adaptation, and strengthened multi‑level governance, to reduce flood risk in semi‑arid cities.