Effects of model complexity on uncertainty estimates

In the Model Complexity working group of BIOMOVS II, models of varying comp lexity have been applied to a theoretical problem concerning downward trans port of radionuclides in soils. The purpose was to study how uncertainty in model predictions varies with model complexity and how model simplificatio ns can suitably be made. A scenario describing a case of surface contaminat ion of a pasture soil was defined. Three different radionuclides with diffe rent environmental behavior and radioactive half-lives were considered: Cs- 137, Sr-90 and I-129. A detailed specification of the parameters required b y different kinds of models was given, together with reasonable values for the parameter uncertainty. A total of seven modelling teams participated in the study using 13 different models. Four of the modelling groups performe d uncertainty calculations using nine different modelling approaches. The m odels ranged in complexity from analytical solutions of a 2-box model using annual average data to numerical models coupling hydrology and transport u sing data varying on a daily basis. (C) 1998 Elsevier Science Ltd. All righ ts reserved.