## 1 Introduction  
Human requirements in the twenty-first century, such as foods, fibers, clean water, and clean air, cannot be met without healthy soil [1]. Soils are an essential component of earth system functions that facilitate the supply of essential ecosystem services [2, 3]; however, the soil may be degraded by human activities and environmental stressors [4]. Population increase, deforestation, and overgrazing are the three major factors that cause and exacerbate soil erosion [5]. Frosion has many negative effects that are of real concern for a variety of reasons. Firstly, removal of the fertile top layer of soil (topsoil) by erosion affects soil fertility and crop productivity. Secondly, erosion diminishes reservoir capacity and operation and degrades downstream water quality [6, 7, 8]. Thirdly, soil erosion causes a rise in pollutants and sedimentation in streams and rivers, resulting in the blockage of these waterways as well as a reduction in biodiversity [9]. Fourthly, erosion also transports soil-laden water downstream, which may produce sediment layers that impede the flow of streams and rivers and ultimately cause floods [10]. Lastly, erosion destroys the land that can host fewer plants capable of absorbing climate-warming carbon dioxide. In a given year, soils might theoretically store enough greenhouse gases (GHG) to equal around five percent of all human-made GHG emissions [11]. An approximate estimate indicates that 10 million hectares of croplands are ruined annually owing to soil erosion. Due to this, agricultural output decreases, resulting in declining economies and a rise in malnutrition [12]. In the Shatt Al-Arab basin, a trans-boundary basin between Iraq and Iran, soil erosion is a severe and complicated environmental problem [13; 14]. The soil erosion rates in Iran, where most of the basin is situated, are twenty times the world average. Soil erosion treatment costs Iran between USD 56B and USD 112B, which is more than the nation's annual oil earnings (e.g., USD 53.6B in 2014) [15]. Moreover, degraded areas are often less capable of retaining water, which may exacerbate floods. For instance, massive flash floods in the Shatt Al-Arab basin in 2019 [16] destroyed livelihoods and caused billions of dollars in damage in Iraq and Iran [17; 18]. In the region of Khuzestan, where the Shatt Al-Arab basin extends, roughly 18 tons of soil per hectare is eroded each year [19]. Khuzestan province ranks first in Iran due to the high soil erosion rates. Such high erosion levels restrict the viability of agricultural endeavors [20]. In other instances, soil erosion has led to an increase in dust pollution in this area, which has harmed the habitability of rural households [21; 22; 23]. Moreover, sedimentation caused by erosion affects the storage capacity of dams by about 0.2 billion cubic meters each year. Likewise, Iran's agricultural land loses are around 33-ton ha\({}^{-1}\)year\({}^{-1}\) of soil due to erosion. A ton of soil encloses around 28 km of nitrogen, phosphorus, and potassium. Consequently, approximately 900 km of nutrients per hectare are lost [24]. Based on the average cost of fertilizers, the annual damage of nutrient loss due to soil erosion is around USD 2.7B [25]. The above-described erosional degradation results in enormous economic impacts in the upper parts of the basin. Moreover, the downstream parts of the basin have a limited potential for soil erosion. Yet, materials that are eroded from the upstream parts may compile in the river's lower reaches, imposing further economic damages [14]. Studies conducted on soil erosion in the Shatt Al-Arab basin were limited to the Iranian part of the basin, e.g., [26; 27]. Such studies were valuable in their own terms. However, they were constrained to specific sites within the basin. Therefore, it is not possible to thoroughly identify the spatial distribution characteristics of the soil erosion in the entire basin.