STOCHASTIC CALIBRATION OF AN OROGRAPHIC PRECIPITATION MODEL

In this study a stochastic approach to calibration of an orographic pr ecipitation model (Rhea, 1978) was applied in the Gunnison River Basin of south-western Colorado. The stochastic approach to model calibrati on was used to determine: (1) the model parameter uncertainty and sens itivity; (2) the grid-cell resolution to run the model (10 or 5 km gri ds); (3) the model grid rotation increment; and (4) the basin subdivis ion by elevation band for parameter definition. Results from the stoch astic calibration are location and data dependent. Uncertainty, sensit ivity and range in the final parameter sets were found to vary by grid -cell resolution and elevation. Ten km grids were found to be a more r obust model configuration than 5 km grids. Grid rotation increment, te sted using only 10 km grids, indicated increments of less than 10 degr ees to be superior. Basin subdivision into two elevation bands was fou nd to produce 'optimal' results for both 10 and 5 km grids. (C) 1998 J ohn Wiley & Sons, Ltd.