Using the Water Erosion Prediction Project (WEPP) model to simulate field-observed runoff and erosion in the Apennines mountain range, Italy

Summary

The Water Erosion Prediction Project (WEPP) model was tested using data from a detailed study conducted on experimental plots in the Apennines Mountain Range, northern Italy. Runoff, soil water and sediment data, together with weather information, were collected on an hourly basis at the study site. WEPP was first applied to simulate transient surface runoff, soil water and erosion. Two important input parameters, the biomass energy ratio for crop and the effective hydraulic conductivity of surface soil, were calibrated using field-observed runoff, soil water, erosion and plant biomass data. The calibrated model was then used to simulate the hydrologic and erosion impacts of three typical crop rotations, thereby to evaluate their abilities in reducing surface runoff and sediment yield. Results indicated that, with the definition of a restrictive layer at the bottom of the soil profile and the calibration of the two crucial model parameters, WEPP could adequately account for the water balance for the modeled experimental plot. For the study area, continuous corn with a conservation practice that delayed primary and secondary tillages produced low surface runoff and soil erosion, from both field observation and WEPP modeling. However, this mono-cultural practice may lead to accelerated soil-quality degradation. On the other hand, a four-year-rotation, corn–wheat–alfalfa–alfalfa, was predicted to substantially reduce soil erosion and has potential to become a sustainable cropping system under the pedo-climatic settings of the study area.

Introduction

Across the world, increasing attention has been devoted to issues of sustainable agricultural production and natural resource management. Among these issues, soil conservation plays a fundamental role, because soil is unarguably the most important resource for agricultural production (Gijsbers et al., 2001). As world population increases, arable, fertile land becomes scarcer, and land use tends to be intensified, which often results in soil degradation.

One of the most important phenomena leading to soil degradation is water erosion on crop lands. Soil erosion is a process that causes loss of fertile topsoil and sedimentation and pollution of surface water bodies. It is a serious agricultural and environmental problem in many areas of the world (Brown and Wolf, 1984). In the United States, soil erosion from cultivated areas often occurs at a high rate. In 1997 alone more than 40 Mha of crop lands have been reported to be affected by water erosion, with annual losses of 25 t ha⁻¹ (Lal et al., 2004). However, the exact magnitude of the problem in the United States is still a subject of debate, and many researchers stress the need to develop a national soil erosion monitoring system to better study the problem (Trimble and Crosson, 2000).

In many regions of Europe, water erosion from agricultural fields can also be severe (Brazier et al., 2000). For instance, in the clayey areas of the North Apennines Mountain Range in Italy, crop-land erosion has been increasing as a result of intensified agricultural activities during the last century (Rossi Pisa et al., 1999). Controlling water erosion to preserve soil quality and to maintain agricultural productivity is therefore a great challenge and one of the most pressing environmental issues.

Lal (1998) and Toy et al. (2002) provide an overview of the soil erosion phenomena and common applied research methods. Among the available tools to assess soil erosion, prediction models have become important because adequate and reliable models can be used to evaluate a variety of management scenarios without costly and lengthy field tests.

The Water Erosion Prediction Project (WEPP) model is one of the most utilized tools for simulating water erosion and sediment yield. WEPP has been tested and applied in different geographic locations across the United States (Savabi, 1993, Savabi et al., 1995, Huang et al., 1996, Laflen et al., 2004), in Australia (Rosewell, 2001) and in the United Kingdom (Brazier et al., 2000). However, application of WEPP in the Mediterranean environment has been lacking in the literature. To our knowledge there has been only one study using WEPP for modeling erosion in the hilly area of Sicily (Spadaro et al., 2004). Runoff and soil erosion data collected from twelve plots with different cropping systems were used to assess the performance of the WEPP model. The authors reported generally acceptable indices of model efficiency. Further, when input values of effective soil hydraulic conductivity and critical shear were adjusted, the WEPP prediction was improved, with the Nash–Sutcliffe index values of 0.82 for runoff and 0.88 for soil loss. Overall, they found that WEPP has potential for simulating runoff and soil losses under Mediterranean conditions.

For many years, a comprehensive field experimental facility has been operating at the Centonara Watershed in the Apennines Mountain Range near Bologna, northern Italy. The field facility continuously monitors surface runoff, runoff chemicals, sediments and soil water content as well as important weather parameters.

The goal of our study was to evaluate the suitability of the WEPP model in simulating water balance (including runoff, soil water and evapotranspiration) and erosion. Specific objectives were to: (i) test and calibrate the WEPP model for hydrologic and erosion modeling under the Mediterranean climate conditions, and (ii) apply the calibrated model to assess the impact of three typical cropping systems on runoff and erosion reduction.