Decadal climate prediction aims to improve near-term (10-30 years) climate change projection by using the experiences of weather forecasting and seasonal climate prediction. It has raised wide concern since the implementation of Coupled Model Intercomparison Project Phase 5 (CMIP5), and the climate community is now trying to turn the decadal prediction from pure research to a quasi-real-time operational effort. However, very limited information is known about decadal hydrological predictability over land, which is more relevant to the water resource and infrastructure management.