# Soil Erosion Estimates in Arid Region: A Case Study of the Koutine Catchment, Southeastern Tunisia
###### Abstract
[19] in the south of Tunisia explained that soil erosion is more vigorous when rainfall is very intense, but it does not follow a linear relationship with rainfall rate and area exposed to erosion. Under laboratory flume-controlled conditions, however, it was found that soil loss is proportional to the area exposed during the steady-state equilibrium and when interrill is the dominant erosion mechanism. At the same time, at the beginning of the erosive event, the relationship is less clear due to the pronounced influence of soil's antecedent conditions [20; 21]. Therefore, during heavy storm events, the concentrated fill erosion becomes the dominant soil erosion process, especially under compacted and bare toposoil conditions, resulting in a substantial soil loss. For contour-plowed soil, however, only an exceptional rainfall on wet toposoil conditions causes fill and interrill erosions [19]. In order to attenuate the soil erosion problem, numerous soil and water management options are increasingly implemented. However, the changing climate conditions, including seasonality and spatiotemporal variability, reduce these mitigation measures' effectiveness. Decision-makers need a detailed understanding of soil erosion drivers, states and impacts in order to better guide mitigation intervention that require thorough spatial soil erosion investigation at the sub-catchment level. Soil erosion modeling has shown to be a beneficial tool for predicting and describing soil erosion processes and evaluating soil losses and their controlling factors [1]. In arid regions, lack of systematic monitoring and data sharing are commonly limiting factors for modeling use. For instance, installing permanent monitoring devices for soil erosion in a typical dry area is a major challenge due to weather conditions, vandalism and technical problems (such as lack of power, appropriate maintenance and presence of dust). Therefore, numerous studies have considered rainfall simulation and/or existing natural or human-made erosion collection structures (such as cisterns, buffer strips, etc.) as appropriate approaches to investigate soil erosion processes and yields. One of the first models used was the USLE (Universal Soil Loss Equation) model introduced by the US Department of Agriculture (USDA) [22]. Later, it was revised [23] and retitled to RUSLE (Revised Universal Soil Loss Equation), which produces a spatial distribution of soil erosion and could be applied by decision-makers for conservation and management processes [24]. Northern regions of Tunisia have benefited from some studies such as [15; 25; 26; 27; 28; 29; 30]. RUSLEmodel, adapted to the semi-arid conditions in central Tunisia, provided good estimation results of measured soil erosion delivery [28; 31]. However, using this model, few studies are conducted in the arid regions characterized by the short and violent character of their rainfall events and have very remarkable erosion yields. This study is one step in that direction, where the spatial variability of soil loss in the Koutine catchment has been intensively investigated for 4 years. This study presents a soil erosion assessment methodology in data-scarce and dry areas combining field measurement and modeling. The objectives of this study are to (i) assess the spatial variability of soil erosion in the Koutine catchment and its controlling factors, (ii) quantify the soil losses using intensive field campaigns and laboratory analysis and (iii) to evaluate the RUSLE soil erosion model using the in situ data. The validated model provides the basis upon which decision-makers can test the efficiency of different soil erosion mitigation measures using a scientifically based tool.