Assessment of the prediction error in a large-scale application of a dynamic soil acidification model |
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Authors: | J Kros J P Mol-Dijkstra E J Pebesma |
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Institution: | (1) Alterra, Green World Research, P.O. Box 47, 6700 AA Wageningen, Netherlands, NL;(2) University of Utrecht, Faculty of Geographical Sciences, Netherlands, NL |
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Abstract: | The prediction error of a relatively simple soil acidification model (SMART2) was assessed before and after calibration,
focussing on the Al and NO3 concentrations on a block scale. Although SMART2 is especially developed for application on a national to European scale,
it still runs at a point support. A 5×5 km2 grid was used for application on the European scale. Block characteristic values were obtained simply by taking the median
value of the point support values within the corresponding grid cell. In order to increase confidence in model predictions
on large spatial scales, the model was calibrated and validated for the Netherlands, using a resolution that is feasible for
Europe as a whole. Because observations are available only at the point support, it was necessary to transfer them to the
block support of the model results. For this purpose, about 250 point observations of soil solution concentrations in forest
soils were upscaled to a 5×5 km2 grid map, using multiple linear regression analysis combined with block kriging. The resulting map with upscaled observations
was used for both validation and calibration. A comparison of the map with model predictions using nominal parameter values
and the map with the upscaled observations showed that the model overestimated the predicted Al and NO3 concentrations. The nominal model results were still in the 95% confidence interval of the upscaled observations, but calibration
improved the model predictions and strongly reduced the model error. However, the model error after calibration remains rather
large. |
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Keywords: | : Environmental modelling Soil science Calibration Validation Model error |
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