Comparing global and local calibration schemes from a differential split-sample test perspective

Abstract

This work explores the performances of the hydrologic model Hydrotel applied to 36 catchments located in the Province of Québec, Canada. A local calibration (each catchment taken individually) and a global calibration (a single parameter set sought for all catchments) schemes are compared in a differential split-sample test perspective. Such a methodology is useful to gain insights on a model's skills under different climatic conditions, in view of its use for Climate-Change (CC) impact studies. The model was calibrated using both schemes on five non-continuous dry and cold years and then evaluated on five dissimilar humid and warm years. Results indicate that, as expected, local calibration leads to better performances than the global one. However, global calibration achieves satisfactory simulations while producing a better temporal robustness (i.e. model transposability to periods with different climatic conditions). Global calibration, in opposition to local calibration, thus imposes spatial consistency to the calibrated parameter values, while locally adjusted parameter sets can significantly vary from one catchment to another due to equifinality.. It is hence stated that a global calibration scheme represents a good trade-off between local performance, temporal robustness, and the spatial consistency of parameter values, which is for example of interest in the context of ungauged catchments' simulation, climate-change impact studies, or even simply large-scale modeling.