Abstract
The migration and fate of pesticides in natural environments is highly complex. At the hillslope scale, the quantification of contaminant fluxes and concentrations requires a physically based model. This class of model has recently been extended to include coupling between the surface and the subsurface domains for both the water flow and solute transport regimes. Due to their novelty, the relative importance of and interactions between the main model parameters has not yet been fully investigated. In this study, a global Sobol sensitivity analysis is performed on a vineyard hillslope for a one hour intensive rain event with the CATHY (CATchment HYdrology) integrated surface/subsurface model. The event-based simulation involves runoff generation, infiltration, surface and subsurface solute transfers, and shallow groundwater flow. The results highlight the importance of the saturated hydraulic conductivity K s and the retention curve shape parameter n and they reveal a strong role for parameter interactions associated with the exchange processes represented in the model. The mass conservation errors generated by the model are lower than 1% in 99.7% of the simulations. Boostrapping analysis of sampling methods and errors associated with the Sobol indices highlights the relevance of choosing a large sampling size (at least N = 1000) and raises issues associated with rare but extreme output results.
Highlights
Pesticide use in agricultural catchments leads to widespread surface and subsurface water contamination
The approach used by [51] is chosen as it is able to deal with NA values, in the case where a simulation has not succeeded, which can happen in practice with numerically complex models such as CATHY
First order indices and total indices results are presented after the convergence of Sobol indices, namely with the extraction of 57 simulations whose results are replaced with NA
Summary
Pesticide use in agricultural catchments leads to widespread surface and subsurface water contamination. Some models represent comprehensive transfer processes, including preferential flow, reactive processes, and root uptake, at the plot scale [1,2,3,4,5]. These models generally simulate transfers in one dimension (soil column) and do not represent processes that are significant at the catchment scale such as lateral fluxes and surface/subsurface interactions. They lack connectivity and discontinuity representation, which plays an important role for pesticide transfer. A second group, the integrated surface/subsurface hydrological models (ISSHMs), is less detailed on reactive solutes at the fine scale but resolves surface
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