Exploration of sub-annual calibration schemes of hydrological models

摘要

This study has compared hydrological model performances under different sub-annual period calibration schemes using two conceptual models, IHACRES and HYMOD. In several publications regarding sub-annual period calibration, the authors showed that such an approach generally performed better than the conventional whole period method. Hence, there are advantages in dividing (or clustering) the data into sub-annual periods for calibration. However, little attention has been paid to the issue of how to calibrate the non-continuous sub-annual period. It is therefore important to explore reliable calibration schemes for such a situation. Unlike the conventional whole period calibration which assumes time-invariant parameters for the entire calibration period, the model parameters vary in sub-annual calibration. We have explored two sub-annual calibration schemes, serial calibration scheme (SCS) and parallel calibration scheme (PCS). We assume that the relationships between the rainfall and runoff could be different for each sub-annual period and consider intra-annual variations of the system. The models are then evaluated for a different validation period to avoid over-fitting (or, over parameterisation) and the optimal sub-annual calibration period is explored. Overall, we have found that PCS performed slightly better than SCS and the optimal calibration periods are seasonal and bimonthly for IHACRES and biannual for HYMOD at the study catchment. Since there are pros and cons in both SCS and PCS, we recommend choosing the method depending on the purpose of the model usage. Although the catchment is specific in the study, the methodology proposed is general and applicable to other catchments.