Spatial uncertainty analysis of pesticide leaching using a metamodel of PEARL

Ton van der Linden 1, Aaldrik Tiktak 2, Gerard Heuvelink 3 and Toon Leijnse 4
1 National Institute for Public Health and the Environment
PO Box 1, 3720 BA Bilthoven, The Netherlands
Tel.: + 0031 30 274 3342; Fax: + 0031 30 274 4413
ton.van.der.linden@rivm.nl
2 Netherlands Environmental Assessment Agency
PO Box 303, 3720 AH Bilthoven, The Netherlands 
Tel.: + 0031 30 274 3343; Fax: + 0031 30 274 4419
aaldrik.tiktak@mnp.nl
3 Soil Science Centre, Wageningen University and Research Centre
PO Box 47, 6700 AA Wageningen, The Netherlands.
Tel.: + 0031 30 274 3343; Fax: + 0031 30 274 4419
gerard.heuvelink@wur.nl
4 TNO Environment and Geosciences
PO Box 80015, 3508 TA Utrecht, The Netherlands
Tel.: + 0031 30 274 3343; Fax: + 0031 30 274 4419
toon.leijnse@tno.nl

Abstract
Spatially distributed modelling has recently been introduced in pesticide registration procedures and policy evaluations. The assessments are quite demanding with respect to computational efforts, which probably is the reason that little attention has been paid so far to uncertainty analyses of leaching concentrations at the regional scale. Recently, a metamodel of pesticide leaching was developed and calibrated with results of the spatially distributed model EuroPEARL (Tiktak, et al. 2004; Tiktak, et al. (acc.)). The metamodel is based on an analytical expression of the transport of solutes through porous media and calculates the fraction of the applied amounts which leach to a reference depth in the soil profile. Important inputs to the metamodel are the half-life and sorption constant of a pesticide, soil organic carbon content and soil moisture at field capacity, as well as long-term averages of temperature and precipitation surplus. The  metamodel explained more than 90% of the variance in the simulation results and thus might be considered a good approximation of the original model. As opposed to the original model, the metamodel is very inexpensive with regard to computational efforts, which makes it suitable for calculations at high resolutions (i.e. small grid sizes) or uncertainty analyses using Monte Carlo  techniques. Using the metamodel, this paper investigates the uncertainty in pesticide leaching assessments due to uncertainty in the half-life and sorption constant of pesticides and uncertainty and spatial variability in soil parameters and climatic conditions. The magnitude of uncertainty in the annual leached pesticide is computed for the  temperate region of the EU and the relative contributions of individual uncertain inputs are compared.  Possible implications for policy evaluations are discussed.

Keywords: groundwater, spatial correlation, error propagation, Monte Carlo simulation

In: Caetano, M. and Painho, M. (eds). Proceedings of the 7th International Symposium on Spatial Accuracy Assessment in Natural Resources and Environmental Sciences, 5 – 7 July 2006, Lisboa, Instituto Geográfico Português

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