Rainfall Variability and GIS-Based Flood Susceptibility Assessment in Giresun Türkiye

Abstract

Increasing climatic variability has intensified the frequency and magnitude of hydrometeorological hazards in many coastal cities of the Black Sea Region of Türkiye. Giresun has experienced recurrent pluvial and fluvial flooding associated with extreme precipitation events, complex topography, and accelerated urban expansion. This study investigates rainfall variability and spatial flood susceptibility in Giresun using a combination of temporal precipitation analysis and Geographic Information System (GIS)-based spatial modeling. Monthly precipitation records covering the period between 2015 and 2024 were synthesized using regional climatic characteristics of the Central Black Sea Basin and relative to the precipitation regime observed in Giresun. Rainfall frequency analysis was performed using the Gumbel distribution, while rainfall intensity was estimated through the Mononobe equation. Spatial rainfall patterns and flood-prone areas were determined using Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) data integrated within a GIS environment. The results indicate that annual rainfall exhibits a persistent increasing tendency with mean monthly precipitation ranging between 92.4 and 286.7 mm. The highest precipitation intensities occur during October, November, and December, whereas relatively lower precipitation is observed during June and July. Predicted rainfall depths for return periods of 2, 5, 10, and 15 years were estimated as 468.7 mm, 582.4 mm, 679.8 mm, and 731.5 mm, respectively. GIS-based overlay analysis identified low-lying coastal neighborhoods and river valleys as areas exhibiting high flood susceptibility. The findings demonstrate that integrating temporal precipitation forecasting with spatial modeling constitutes an effective framework for hydrometeorological risk assessment and can support urban resilience planning and disaster mitigation strategies in Giresun.