INVESTIGATING THE IMPACTS OF DIFFERENT TIME INTEGRATION METHODS IN LAND SURFACE MODELS ON RUNOFF ESTIMATION

Abstract

 In this study, the impacts of time integration methods on runoff estimation were investigated in two land surface models (LSMs): MRI-SiB and SiBUC. Both models were forced by the same atmospheric data from MRI-AGCM 3.2 with 20-km spatial resolution. For updating soil moisture, SiBUC implements an explicit midpoint method, while MRI-SiB applies a semi-implicit method. In this research, two simulation cases were performed by SiBUC by changing different time integration methods. It was found that applying different time integration methods affected the runoff characteristics. The simulation by the explicit method resulted in higher surface runoff than subsurface runoff. On the other hand, the results by the semi-implicit method showed the opposite characteristics. Analysis of the simulated discharge show the different responses of the estimated flow to the rainfall due to the change in the ratio between surface and subsurface runoff. It is thought that a semi-implicit scheme is one of the key factors of low surface runoff in MRI-SiB.