Background Scale effect on runoff is a frontier and hot issue in the field of hydrology and water resources. Since the end of the 1980s, many researchers in China have carried out a wide range of related studies across the country. However, the existing relevant review articles have not yet systematically and quantitatively analyzed the study of the scale effect on runoff in China from the overall progress and regional distribution.

Methods Based on the 517 pieces of literature in six bibliometrics databases and through the method of word frequency analysis, we reviewed the studies of the scale effect on runoff in China. Specifically, we summarized the studies from the development history, research topics, research institutions, distributions of spatial and temporal scale, study areas, research methods, and mathematical models. The searching pattern in the CNKI database was Title=(((runoff OR hydrolog* OR flood OR "overland flow" OR "base flow" OR "stream flow" OR "river flow) AND (*scale OR *scaling) NEAR/1 (*temporal OR time* OR spatial* OR spatio* OR different OR multi* OR effect OR affect OR impact OR influence OR dependent OR transf* OR convers* OR analy* OR issue)).

Results 1) The development history of relevant research could be divided into three stages: the initial stage from 1989 to 2000, the rapid development stage from 2001 to 2006, and the stable development stage after 2007. 2) Inter-yearly scale and rainfall event scale predominated in the temporal scales; watershed-scale predominated in the spatial scales. 3) Regarding the river basins, the Yellow River and Yangtze River were the main study areas. Regarding the soil and water conservation zones, considerable studies were conducted in the northwestern Loess Plateau, and then followed by the southwestern purple soil region, southern red soil region, and northern hilly and mountainous region. Regarding the terrain types, many studies were clustered in the plateau, and then followed by mountain, hill, and plain. Regarding the climate zones, most study areas were located in humid and semi-humid areas that had adequate rainfall as well as in warm temperate, subtropical, and mid-temperate zones that had a suitable temperature. 4) There were a wide variety of research methods, and different research methods and numerical models were applicable to different temporal and spatial scales.

Conclusions Overall, the scale issue of runoff or hydrology still has an urgent need for further exploration and discussion. Research on the spatio-temporal scale issues of flood processes regarding extreme rainstorms should be further strengthened. Also, attention should be paid to the subjects of scale effect on hydrological connectivity, variable-scale hydrology model, and scale conversion. This review may provide basic data for a systematic understanding of the research status quo of the scale issue in hydrology in China, as well as directions for future research and work in the fields of hydrology and soil and water conservation.