Sensitivity analyses for the FOCUS leaching models

Systematic sensitivity analyses using two different approaches tone-at-a-ti me and Monte Carlo techniques) were carried out for all four FOCUS leaching models (PELMO, PESTLA, PRZM and MACRO). Four scenarios were used comprisin g two hypothetical pesticides and either a sandy soil or a more structured medium loam soil. This paper presents results for PELMO 3.00 and the prefer ential flow model MACRO 4.1. Predictions of percolation by the two models w ere only slightly affected by a few input parameters. In comparison, pestic ide losses were affected by numerous parameters and extremely large sensiti vities were noted. In most scenarios, pesticide losses predicted by the two models were most affected by sorption and degradation parameters. However, investigations for one scenario involving a structured clay loam with MACR O revealed that, under specific circumstances, pesticide losses can be more affected by changes in hydrological properties of the soil.