Regional variability can be modelled using the Monte-Carlo technique whereby input parameters are described by distributions rather than site values. The parameters required include weathering rates for base cations, soil depths and porosities, rainfall, cation exchange capacities, exchangeable base fractions on cation exchange sites and chemical inputs. The model is run repeatedly with random choices of parameter sets selected from the defined population distribution. On completion, the successful calibrations are matched to the observed distribution using a weighting procedure.
Reference
Sefton., C.E.M and Jenkins, A. A regional application of the MAGIC model in Wales: calibration and assessment of future recovery using a Monte-Carlo approach. Hydrology and Earth System Sciences, Special Issue The DYNAMO Project Vol 2 (4) 521-531, 1998.