[Discussion on hydrologic scaling].

Hydrologic scaling is the hotspot and frontier of today's hydrologic research, which includes three different meanings distinguished from each other, i.e., process scale, observation scale and modelling scale. As a characteristic of hydrologic scale, dominant process scale has been paid more attention. Hydrologic scaling includes the scaling of hydrologic models, parameters, state variables and inputs, which owns special research methods respectively. The difficulty of hydrologic scaling mainly comes from the organized complexity of hydrologic systems, the heterogeneity and variability in space and time, and the insufficiency of data. The ubiquitous self-similarity of natural river networks makes itself an important part of hydrologic scaling research. The combination of various techniques and theories is needed to motivate hydrologic scaling research.