**1. Introduction**

Erosion and sedimentation refer to the motion of solid particles, called sediment (Julien, 2010). Erosion is a natural process and causes a breakdown of soil aggregates and accelerates the removal of organic and mineral materials (Gilley, 2005).

Soil erosion risk can be assessed by means of equations empirically derived from the superposition principle of this phenomenon. Using such models, during the last decade, several initiatives have assessed the risk of soil erosion at the national, continental, and global levels (Terranova et al., 2009).

The use of geographic information system (GIS) enables the determination of the spatial distribution of the parameters of some soil loss predicting models, as the Universal Soil Loss Equation - USLE (Dabral et al., 2008). Every factor within the USLE is calculated by GIS, which is obtained from meteorological stations, topographic maps, land use maps, soil maps and results of other relevant studies. The spatial distribution of the soil loss of a certain region is given by multiplying factor map layers in the GIS. The spatial resolution of the data is an option of researcher, and should be considered the resolution of the Digital Elevation Model (DEM), soil map, satellite images, among other sources of information (Yue-Qing et al., 2008).

Land use is the only factor affecting erosion that can be modified to reduce soil loss potential (Gilley, 2005). However, if we do not consider the land cover and soil management, i.e., if we consider the interaction of rainfall, topography and soil, assuming that the soil is totally uncovered along wholly study area, we may predict the total soil loss amount or the Natural Potential for Erosion (NPE) for a considered area (Castro & Valério Filho, 1997).

NPE might be used as a tool to show cartographically areas highly pre-disposed to erosion and the mathematic relation among PNE value and soil loss tolerance value. It might indicate the ideal CP factor to be used in determined region.

Brazil is largest South American country and the land use is far from to be conformable with land use capability. Hence, soil loss studies and researches are highly needed. On the other hand, a lot of studies have been developed in order to predict soil loss rates along Brazilian

Natural Potential for Erosion for Brazilian Territory 5

S is a factor for slope steepness (%). C is the cropping management factor and P is conservation practices factor (Wischmeier and Smith, 1978; Beskow et al., 2009). The two last

factors are dimensionless and LS, when managed jointly, are also dimensionless.

Fig. 1. Water erosion vulnerability map. Source: USDA (2003).

**4. Brazilian environmental characteristics** 

is:

The NPE map is generated using the factors related to physical environment (rainfall erosivity, soil erodibility, and topographic factor). Factors C and P, related to human influence (cover management and soil management), are not considered. So, the NPE model

Where: NPE – Natural Potential for Erosion, in t.ha-1.y-1; R, K, LS – same of equation (1).

Brazil extends from the equatorial to the subtropical belt. Environmental characteristics are highly changeable along Brazilian territory due to large territorial size. The country is characterized by a large diversity of soil types, resulting from the interaction of the different

NPE = R K LS (2)

territory. Some of them use GIS technology (Beskow et al., 2009), some use hydrosedimentologic database, or others approaches (Tornquist et al., 2009). But such studies involve only a part of territory (a river basin, for example).

Considering the scarcity of database of a map that presents the Natural Potential for Soil Erosion through a specific mathematical model, this study aims elaborate the NPE map for entire Brazilian Territory considering the USLE approach.

#### **2. Soil degradation**

Soil erosion is a process inherent in landscape evolution. The intensity of soil erosion is governed by numerous natural and anthropogenic factors. Natural factors include soil, climate, vegetation, relief and other ecoregional characteristics (Lal, 2001).

Soils are more exposed to erosion for different reasons: inappropriate agricultural practices, deforestation, overgrazing, forest fires, and construction activities (Terranova et al., 2009). Erosion process has both on-site and off-site consequences. On-site consequences results in the loss of productive topsoil and other physical and chemical consequences. Furthermore, off-site problems, such as downstream sediment deposition in fields, floodplains and water bodies, are also very serious, with significant costs to society (Verspecht et al., 2011).

Land degradation may be defined as long-term adverse changes in soil properties and processes, leading to a loss of ecosystem function and productivity caused by disturbances from which land cannot recover unaided (Bai et al., 2008; Palm et al., 2007). Through such changes in soil properties and processes, soil degradation undermines the sustainability of many of the ecosystem services (Palm et al., 2007).

Among the kinds of degradation, Bai et al. (2008) list water erosion, wind erosion, nutrient depletion, salinity, contamination, physical as the principal ones. Among them, water erosion is responsible by more than a half of the degraded land along world and also in South America.

South American continent is a region with particular and expressive areas presenting high or very high vulnerability for water erosion (Figure 1). It presents average soil loss rates of 16.7 t ha−1 y−1 that is significantly higher if compared to the world average of 11.5 t ha−1 y−<sup>1</sup> (Nam et al., 2003).

#### **3. Soil loss modelling**

Assessment of risk of erosion has traditionally been carried out by application of one of the many available mathematical models (Boardman et al., 2009). Considering that any model is a simplification of reality (Morgan & Nearing, 2011) and, for some users, this creates an immediate theoretical issue, the approach here employed considers three elementary natural features involved in erosion process: climate, relief and soil.

This approach is the Natural Potential for Soil Erosion (NPE). NPE, or Potential Erosion Risk, is defined here as the inherent risk of erosion irrespective of current land use or vegetation cover (Grimm et al., 2002; Vrieling et al., 2002). The NPE map can be generated using a part of the USLE model. The USLE is:

$$\text{A=R K L S CP} \tag{1}$$

Where: A is the rate of soil loss (t ha-1 y-1), R is a factor for annual rainfall erosivity (MJ mm ha-1 h-1 y-1), K is a factor for soil erodibility (t h MJ-1 mm-1), L is a factor for slope length (m),

territory. Some of them use GIS technology (Beskow et al., 2009), some use hydrosedimentologic database, or others approaches (Tornquist et al., 2009). But such

Considering the scarcity of database of a map that presents the Natural Potential for Soil Erosion through a specific mathematical model, this study aims elaborate the NPE map for

Soil erosion is a process inherent in landscape evolution. The intensity of soil erosion is governed by numerous natural and anthropogenic factors. Natural factors include soil,

Soils are more exposed to erosion for different reasons: inappropriate agricultural practices, deforestation, overgrazing, forest fires, and construction activities (Terranova et al., 2009). Erosion process has both on-site and off-site consequences. On-site consequences results in the loss of productive topsoil and other physical and chemical consequences. Furthermore, off-site problems, such as downstream sediment deposition in fields, floodplains and water

Land degradation may be defined as long-term adverse changes in soil properties and processes, leading to a loss of ecosystem function and productivity caused by disturbances from which land cannot recover unaided (Bai et al., 2008; Palm et al., 2007). Through such changes in soil properties and processes, soil degradation undermines the sustainability of

Among the kinds of degradation, Bai et al. (2008) list water erosion, wind erosion, nutrient depletion, salinity, contamination, physical as the principal ones. Among them, water erosion is responsible by more than a half of the degraded land along world and also in

South American continent is a region with particular and expressive areas presenting high or very high vulnerability for water erosion (Figure 1). It presents average soil loss rates of 16.7 t ha−1 y−1 that is significantly higher if compared to the world average of 11.5 t ha−1 y−<sup>1</sup>

Assessment of risk of erosion has traditionally been carried out by application of one of the many available mathematical models (Boardman et al., 2009). Considering that any model is a simplification of reality (Morgan & Nearing, 2011) and, for some users, this creates an immediate theoretical issue, the approach here employed considers three elementary natural

This approach is the Natural Potential for Soil Erosion (NPE). NPE, or Potential Erosion Risk, is defined here as the inherent risk of erosion irrespective of current land use or vegetation cover (Grimm et al., 2002; Vrieling et al., 2002). The NPE map can be generated

Where: A is the rate of soil loss (t ha-1 y-1), R is a factor for annual rainfall erosivity (MJ mm ha-1 h-1 y-1), K is a factor for soil erodibility (t h MJ-1 mm-1), L is a factor for slope length (m),

A=R K L S C P (1)

bodies, are also very serious, with significant costs to society (Verspecht et al., 2011).

studies involve only a part of territory (a river basin, for example).

climate, vegetation, relief and other ecoregional characteristics (Lal, 2001).

entire Brazilian Territory considering the USLE approach.

many of the ecosystem services (Palm et al., 2007).

features involved in erosion process: climate, relief and soil.

using a part of the USLE model. The USLE is:

**2. Soil degradation** 

South America.

(Nam et al., 2003).

**3. Soil loss modelling** 

S is a factor for slope steepness (%). C is the cropping management factor and P is conservation practices factor (Wischmeier and Smith, 1978; Beskow et al., 2009). The two last factors are dimensionless and LS, when managed jointly, are also dimensionless.

Fig. 1. Water erosion vulnerability map. Source: USDA (2003).

The NPE map is generated using the factors related to physical environment (rainfall erosivity, soil erodibility, and topographic factor). Factors C and P, related to human influence (cover management and soil management), are not considered. So, the NPE model is:

$$\text{NPE} = \text{R KLS} \tag{2}$$

Where: NPE – Natural Potential for Erosion, in t.ha-1.y-1; R, K, LS – same of equation (1).
