HR: 14:10h
AN: H13I-03    [Abstracts]
TI: Calibrating a distributed hydrological model in a basin with heterogeneous geology
AU: McMillan, H K
EM: h.mcmillan@niwa.co.nz
AF: NIWA, 10 Kyle Street, Christchurch, 8004, New Zealand
AU: * Clark, M P
EM: mp.clark@niwa.co.nz
AF: NIWA, 10 Kyle Street, Christchurch, 8004, New Zealand
AU: Ibbitt, R P
EM: r.ibbitt@niwa.co.nz
AF: NIWA, 10 Kyle Street, Christchurch, 8004, New Zealand
AB: Calibrating distributed hydrological models is a challenging task because of the large number of model parameters (multiple model parameters for multiple sub-basins). A common approach is to apply a set of "parameter multipliers" to the model parameters in each sub-basin. This significantly reduces the dimensionality of the optimization problem, but can result in a spatial distribution of model parameters that is inconsistent with spatial differences in hydrological processes. More thoughtful calibration strategies are needed, especially in river basins where the geology is heterogeneous. This paper reports on our experience calibrating a distributed hydrological model for the Rangitaiki River basin in New Zealand. The Rangitaiki is an interesting river in that the geology of the western half of the river basin is pumice, which responds slowly to rain events; while the geology of the eastern half of the river basin is greywacke, which responds rapidly to rain events. Several different calibration strategies were tested, each of which modifies the frequency distribution that describes the a-priori parameters assigned to sub-catchments throughout the river basin. The spatial parameters are modified en masse, or modified in clusters according to geographic location or sub-catchment geology. Results show that spatial variability in model parameters is necessary to produce realistic streamflow simulations both at the basin outlet and at interior points in the basin. The required complexity of the calibration strategy depends on the reasonableness of a-priori parameter estimates—if a-priori model parameters are constant across all sub-catchments, then more complex calibration methods are needed to reproduce spatial variability in runoff responses. The results of the analysis are currently being used to design a methodology to estimate model parameters for all river basins throughout New Zealand.
DE: 1805 Computational hydrology
DE: 1816 Estimation and forecasting
DE: 1833 Hydroclimatology
DE: 1840 Hydrometeorology
DE: 1873 Uncertainty assessment (3275)
SC: Hydrology [H]
MN: 2007 Fall Meeting