Modelling intercrop management impact on runoff and erosion in a continuous maize cropping system: Part I. Model description, global sensitivity analysis and Bayesian estimation of parameter identifiability

Abstract

In order to evaluate the long-term impact of intercrop management on runoff and erosion in a continuous maize cropping system a new model was developed, based on the continuous plot-scale runoff model of Laloy & Bielders (2008). This model is called the Continuous Runoff and Erosion Hillslope model with DYnamic soil Surface properties (CREHDYS). This paper details the erosion and crop growth and decay model components and presents a thorough global variance-based sensitivity analysis (GSA) with regard to the erosion prediction, followed by a Bayesian parameter identifiability assessment. As compared with the classical local univariate sensitivity analysis, a GSA is able to deal with the typical non-linearity of process-based hydrological and erosion models. The most influential parameters were the Manning's roughness coefficient followed by the saturated hydraulic conductivity of wheel track cells and the median particle size of the material. The soil aggregate stability and soil-cohesion parameters were found to be almost non-influential. Most of the results of the parameter identifiability procedure were in close agreement with the GSA. Indeed, the parameter uncertainty seemed to be proportional to the degree of influence, with Manning's coefficient being the most precisely identified, whereas soil and wheel track cohesion parameters showed the largest uncertainty. Exceptions were the soil aggregate stability and the Green-Ampt soil matric potential. The uncertainty associated with the former was surprisingly low given its low level of influence whereas the uncertainty associated with the latter is partially explained by its negative correlation with the soil saturated hydraulic conductivities of overland flow and wheel track cells.

Effect of Intercropping Period Management on Runoff and Erosion in a Maize Cropping System

“…However, the 2005-2006 intercropping period was characterized by less-than-average rainfall amounts (Table 2). Th erefore, to confi rm this result, we applied the CREHDYS continuous runoff model (Laloy and Bielders, 2008;2009a) to the 2005-2006 intercropping period, using a typical parameterization of bare crusted intercropping plots (Laloy and Bielders, 2009b). With total runoff volumes of 52 mm at Bonlez and 38 mm at Nodebais, the model results…”

Modelling intercrop management impact on runoff and erosion in a continuous maize cropping system: Part II. Model Pareto multi‐objective calibration and long‐term scenario analysis using disaggregated rainfall

“…In order to evaluate the impact of intercrop management on runoff and erosion in a continuous maize cropping system, the plot scale, continuous and process-based erosion model (CREHDYS) developed by Laloy & Bielders (2009) must be calibrated to take account of its two main outputs, runoff and sediment loss. To do that, a global Pareto multi-objective calibration was applied to these two potentially conflicting objectives, considering daily runoff and periodical erosion rates, for two sites with different slopes and soil textures.…”

“…All of the crop growth sub-model parameters were derived from measurements as described by (Laloy & Bielders, 2009) and the hydrological component has been previously calibrated from measurements and through an optimization procedure (Laloy & Bielders, 2008). Values of the 18 hydrological sub-model parameters can be found for both sites in the work by Laloy & Bielders (2008).…”

“…Among the four erosion-related parameters, the aggregate stability index (As), the soil cohesion of overland flow (Coh, kPa) and wheel track (CohW , kPa) cells and the median soil particle size (d50, μm), a thorough global sensitivity analysis revealed that As, Coh and CohW had very little influence on soil loss prediction (Laloy & Bielders, 2009). These three parameters could therefore be defined from the literature, and d50 therefore remained the only unknown parameter of the erosion component of the model (see Table 1).…”

“…In addition, as for every environmental model, such a model requires a proper calibration and validation before being used as a predictive or planning tool. Laloy & Bielders (2009) present the structure (as well as a thorough sensitivity analysis) of such a model, called the continuous runoff and erosion hillslope model with dynamic soil surface properties (CREHDYS), for which the hydrological component has been previously described and validated (Laloy & Bielders, 2008). The objective of the present paper is therefore to achieve a calibration and validation of the CREHDYS model and to evaluate the impact of the cover crop management on runoff and erosion in a continuous maize cropping system through long-term scenario analysis.…”