# Soil Erosion Estimates in Arid Region: A Case Study of the Koutine Catchment, Southeastern Tunisia
###### Abstract  
Soil erosion remains one of the principal environmental problems in arid regions. This study aims to assess and quantify the variability of soil erosion in the Koutine catchment using the RUSLE (Revised Universal Soil Loss Equation) model. The Koutine catchment is located in an arid area in southeastern Tunisia and is characterized by an annual mean precipitation of less than 200 mm. The model was used to examine the influence of topography, extreme rainstorm intensity and soil texture on soil loss. The data used for model validation were obtained from field measurements by monitoring deposited sediment in settlement basins of 25 cisterns (a traditional water harvesting and storage technique) over 4 years, from 2015 to 2018. Results showed that slope is the most controlling factor of soil loss. The average annual soil loss in monitoring sites varies between 0.01 and 12.5 t/ha/y. The storm events inducing the largest soil losses occurred in the upstream part of the Koutine catchment with a maximum value of 7.3 t/ha per event. Soil erosion is highly affected by initial and preceding soil conditions. The RUSLE model reasonably reproduced (R\({}^{2}\) = 0.81) the spatiotemporal variability of measured soil losses in the study catchment during the observation period. This study revealed the importance of using the cisterns in the data-scarc dry areas as a substitute for the classic soil erosion monitoring fields. Besides, combining modeling of outputs and field measurements could improve our physical understanding of soil erosion processes and their controlling factors in an arid catchment. The study results are beneficial for decision-makers to evaluate the existing soil conservation and water management plans, which can be further adjusted using appropriate soil erosion mitigation options based on scientific evidence. soil erosion; RUSLE; GIS modeling; remote sensing; Koutine catchment; geospatial analysis 23 June 2021 16 July 2021 23  
variability and human activity affect runoff and sediment load changes. They are essential factors in explaining the observed variation. However, as the effect of both are integrated at the catchment scale, accurate determination of exactly which part of the observed changes were due to climate variability and which to human activity remains extremely difficult [10]. Soil erosion and land degradation constitute major concerns of different countries in North Africa, such as Tunisia. In this region, the climate is influenced by the Mediterranean Sea to the North and the Sahara desert to the South. The arid, semi-arid and desert bioclimates cover more than two-thirds of the country [11]. The rainfall regime is known for its scarcity, high spatiotemporal variability, torrentiality and poor distribution [12]. Water erosion degrades annually around 15,000 ha of fertile arable soil in Tunisia [13]. The Tunisian arid zones located in the south part of the country cover over 6,290,000 ha, classified as 12% very degraded, 40% medium degraded, 17% marginally degraded and 31% not degraded areas [14]. [PERSON] et al. [15] evaluated erosion risk in semi-arid regions based on extreme rainfall characteristics. These kinds of investigations are crucial for decision-makers for better management and designing intervention priorities against soil erosion risks at the catchment scale. For instance, bench terraces have been recommended as effective soil erosion mitigation options by reducing runoff, erosion and sediment transport on the hillslope [16; 17]. Soil erosion due to extreme rainfall events is an exceptionally dynamic, distributed and complicated process. It is affected by many factors, among them the topography, vegetation and soil type. Furthermore, soil erosion processes during extreme rainfall events are strongly influenced by the spatiotemporal variability of rainfall characteristics [18]. An experimental study conducted by [PERSON] et al.