Hydrological processes are complex and have been changing due to the dual impacts of climate change and human activity, and modeling the hydrological processes and changes has long been the goal of the global hydrological communities. Challenges still exist, such as the lack of effective models and in situ observation data, as well as uncertainties. This special issue aims to discuss these challenges, propose solutions, and report the latest results, it will be a contribution to the IAHS Panta Rhei from its working group on modeling hydrological processes and changes, and all authors from the world's hydrological communities are welcome to submit appropriate manuscripts. Topics to be addressed include but are not limited to the following.

1. In situ and remote sensing observations of hydrological processes and changes, including but not limited to precipitation, evapotranspiration, soil moisture, surface runoff, groundwater, floods, drought, landslides and mudflows.
2. Hydrological models and tools that could be employed to simulate hydrological processes and changes, their associated uncertainties and controlling methods; distributed hydrological models are particularly welcome.
3. Simulation of hydrological processes and changes to large rivers and greater urbanized areas in different climate zones.