Soil properties and flood vulnerability in a semi-arid watershed: The case of Oued Tinn, Algeria

Flooding is a major hazard in semi-arid regions, where intense but irregular rainfall interacts with fragile soils. Assessing soil properties is essential for understanding vulnerability and supporting effective watershed management. This study analyzes the physicochemical characteristics of soils in the Oued Tinn watershed (northwestern Algeria), part of the Macta basin, with the aim of evaluating their susceptibility to flooding caused by rainwater stagnation. Forty soil profiles were collected across 29 sub-watersheds and analyzed for texture, pH, organic matter, calcium carbonate, electrical conductivity, and total nitrogen. Multivariate statistical methods, including Principal Component Analysis (PCA) and Hierarchical Ascending Classification (HAC), were applied to identify the main factors influencing hydrological behavior and to classify soils into vulnerability groups. Results showed that soils are predominantly clayey to clay-loam, with neutral to basic pH, low organic matter, and moderate calcium carbonate content. PCA highlighted texture and carbonate levels as the primary drivers of variability, while HAC grouped the profiles into five distinct classes. Clay- and silt-rich soils with high carbonate content emerged as the most vulnerable due to low permeability, whereas sandy soils were less prone to stagnation but more exposed to fertility loss and erosion. These findings emphasize the need to integrate soil properties into flood risk assessments in semi-arid landscapes. The combined use of soil analysis, multivariate statistics, and spatial mapping provides a replicable framework for identifying high-risk areas and guiding sustainable land-use and soil conservation practices under increasing climatic pressures.