DEVELOPMENT OF REGIONAL PARAMETER-ESTIMATION EQUATIONS FOR A MACROSCALE HYDROLOGIC MODEL

A methodology for developing regional parameter estimation equations, designed for application to continental scale river basins, is describ ed. The approach, which is applied to the two-layer Variable Infiltrat ion Capacity (VIC-2L) land surface hydrologic model, uses a set of 34 unregulated calibration or ''training'' catchments (drainage areas 10( 2)-10(4) km(2)) distributed throughout the Arkansas-Red River basin of the south central U.S. For each of these catchments, parameters were determined by: a) prior estimation of two of the model parameters (sat urated hydraulic conductivity and pore size distribution index) from t he U.S. Soil Conservation Service State Soil Geographic Data Base (STA TSGO) data base; and b) estimation of the remaining seven parameters v ia a search procedure that minimizes the sum of squares of differences between predicted and observed streamflow. The catchment parameters w ere then related to 11 ancillary distributed land surface characterist ics extracted from STATSGO, and 17 variables derived from station mete orological data. The seven regression equations explained from 54 to 7 6% of the variance of the parameters, The most frequently occurring an cillary variables were the average permeability, saturated hydraulic c onductivity, and SCS hydrologic Group B (typically soils with moderate ly high infiltration rates) fraction derived from STATSGO, and the ave rage temperature and standard deviation of fall precipitation. The met hod was tested by comparing simulations using the regional (regression equation) parameters for six unregulated catchments not in the parame ter estimation set, The model performance using the regional parameter s was quite good for most of the calibration and validation catchments , which were humid and semi-humid. The model did not perform as well f or the smaller number of arid to semi-arid catchments. (C) 1997 Elsevi er Science B.V.