8 Conclusions

The description and implementation of pesticide runoff varies significantly between models and model types. Leaching models neglect horizontal transport and therefore are barely useful tools to predict pesticide surface runoff. In contrary, erosion models elaborate surface transport, but do not consider any degradation or transformation between soluble and particle-bound phases. Hydrological models apparently provide the most robust estimates of pesticide runoff and work from medium to large scales. However, hydrological models reveal deficits in temporal resolution and often need to be improved considering pesticide attenuation during transport. Their combination with leaching models delivers realistic results from small to large scales, but there is still a need for a model combination applicable to a wide range of landforms. In order to calculate pesticide emissions on large scales with high certainty, probabilistic approaches could be useful if they were based on deterministic models rather than on simple empirical models.

Future modelling should therefore find standard procedures to apply probabilistic approaches. Generally, deterministic models have to incorporate newly gained knowledge by empirical investigations continually, in order to improve the model performances with regard to sorption behaviour, effects of diversely structured vegetation patches, and small-scale geomorphological structures on pesticide transport. For the same reasons, pesticide models not only have to be improved qualitatively, but they also have to gain higher temporal and spatial resolutions, as we demonstrated that some hydrological models overestimated pesticide loads due to low temporal resolution. However, the resolution of pesticide models is additionally limited by the resolution of available input data and by computer hardware, the latter of which is supposed to experience further rapid improvements.

In summary, the modelling of pesticide runoff has experienced great progress since the early stages in the 1970s, but until now there is no ultima ratio that enables to predict pesticide emissions accurately from small to large scales.