Advances on the research into the mechanism of hydrological cycle in Yellow River catchment
黄河流域水循环研究的进展和展望

The advances on the research into the mechanism of hydrological cycle in Yellow River drainage basin are generalized from four aspects. Firstly, it is shown that the researches on hydrological processes have mainly focused on the single aspects such as precipitation, evaporation, infiltration, interception and runoff. Further studies should focus on the coupling between vertical water transfer and horizontal water movement, with special attention to the prominent characteristics of Yellow River such as man made dry out and high silt content. Secondly, the research results at several hydrological field experimental stations and hydrological laboratories are generalized. These stations and laboratories accumulated a large amount of hydrological data of the Yellow River over years. Unfortunately, most of these stations and laboratories ceased to run in the1960s. A new hydrological experimental laboratory, based on an old laboratory, is available soon to explore the key links in the hydrological cycle in Yellow River drainage basin. Appealing is to the government for reforming more old and/or establishing new hydrological experimental installments. They are one of the most important aspects to basic hydrological research Thirdly, the hydrological models used in operational Yellow River flood forecasting are listed. As Yellow River is mostly located in semi arid and arid climatic zone, the hydrological scenarios of the river are very complicated with high spatial variability. Sometimes the empirical method can get better results of hydrological forecasting than hill slope and or conceptual models. Because distributed model can well consider spatial variability, it is worthy to try to establish a distributed model over the Yellow River. The model will couple vertical and horizontal water transfer and movement, be parameterized by making use of remote sensing and field experimental data and interfaced with Global Circulation Model. The model is established for exploring the mechanism of hydrological cycle in Yellow River diainage basin and simulating the responses on land use/land cover change and other environmental changes. Last but not least, the scale problem, which is another key to explore the mechanism of hydrological cycle of Yellow River, is discussed. It rises because theories of many hydrological processes such as infiltration, evaporation, overland flow, sediment transport and subsurface water movement have been developed at small space-time scales. However, predictions are required at much larger space and time scales. These include the scale of large catchments where not only are the basic theories questionable but other processes or controls on spatial and temporal heterogeneity come into play. In essence, the scale problem is a search for connections between nonlinear hydrological theories developed for small scales, and the large scale hydrology of complex natural systems. Representing spatial and temporal variability in models, explori