Assessing Relative Gully Morphometric Change After Extreme Rainfall Events: A UAV- Based GIS Framework Applied to the 2024 DANA in Southern Spain

Abstract

Climate change is intensifying the frequency and impact of extreme weather events, particularly in vulnerable Mediterranean environments. This study investigates relative morphometric changes within a gully system in the Guadalmedina River basin (Málaga, southern Spain) triggered by the 2024 DANA (Depresión Aislada en Niveles Altos), a high- impact convective event that severely affected eastern and southern Spain. UAV- based photogrammetric surveys conducted before and after the DANA event were used to generate high- resolution Digital Elevation Models (DEMs). These datasets were analyzed within an inte grated GIS- based framework designed for relative morphometric change detection. A consistent structure- from- motion work flow was applied to both surveys, and vegetation filtering techniques were implemented to isolate the bare- earth surface and support gully- scale analysis. A suite of 13 geomorphometric variables derived from the DEMs was extracted using SAGA GIS, including slope, curvature metrics, topographic indices, and hydrological descriptors. Principal Component Analysis (PCA) was employed as an exploratory multivariate tool to synthesize correlated terrain variables and to identify dominant morphometric gradients before and after the extreme event. Results reveal substantial relative topographic reorganization following the DANA, including enhanced incision, changes in slope and curvature patterns, and redistribution of erosion–deposition processes. PCA results highlight a core set of influential variables governing gully morphology, while also indicating post- event shifts in terrain organization associated with concentrated runoff and sediment mobilization. Beyond the specific case study, this work demon strates the potential of UAV- derived geomorphometry combined with multivariate GIS analysis to support post- event landscape assessment and climate adaptation studies. The proposed framework is transferable to other environments affected by extreme hydroclimatic forcing and provides a robust approach for analyzing short- term geomorphological responses to climate extremes at high spatial resolution.