Monitoring water erosion is a difficult task, due to its complex and variable occurrence in both time and space. Climate forcing, steep slopes and anthropogenic action are the primary factors that can endanger soil resources. Located in the heart of the country's agricultural cradle, the Jīzān region is experiencing a twofold degradation of its land. It is both qualitative in the alluvial plain and quantitative in the mountainous areas. This is why it is so important to find a methodological and experimental framework that is suitable for the local conditions of the Oued Jouah watershed, which has undergone a twofold soil loss quantification. The work was started by applying an empirical model based on the (EPM) equation, followed by careful experimental verification using results from monitoring the Caesium 137 isotopic tracer. The specific soil loss was around 35.4 T/Ha/year according to the EPM equation and around 25.5 T/Ha/year based on Caesium 137 monitoring. This methodological validation is of crucial importance not only in determining the main sediment-emitting zones and the factors behind slope destabilization, but also in understanding and highlighting the regional context of the erosive dynamics in intertropical regions.