China suffers from frequent floods and droughts, and faces severe water shortage. The water circulation mechanism and water resources evolution laws in river basins have been playing very crucial roles in hydraulic engineering. The water circulation mechanism includes the non-linear relationship of the rainfall-runoff process, as well as the hydrological and ecological mechanisms of “soil-plant-atmosphere” interaction. Climate change and human activities affect the water resources evolution laws and water control, which are the core issues of the water resources research in hydraulic engineering.
For a long time, the rainstorm flood calculation and flood forecast worldwide have been mainly based upon the linear theoretical system, including the Nash unit linear model. Nevertheless, the true process of the hydrological system appears to be non-linear. The “Aug. 1975” Specially Heavy Rainstorm Flood and Cascaded Dam Collapse Event in Henan Province, China, which shocked the whole world, indicated that there were obvious basic defects in the conventional hydrological calculation system and the rainstorm flood conflux linear system model, and that the rainstorm flood forecast and dam overflow flood recheck are not linear. Thereafter, especially heavy flood disasters occurred one after another in the Yangtze River Basin, Songhua River Basin, Liaohe River Basin, and Huaihe River Basin in China. Therefore, flood forecast and flood regulation in the reservoir watersheds of hydraulic projects have become an essential of the basic water circulation study regarding hydraulic engineering.
Contrary to the rainstorm flood issue, the water circulation dynamic process and ecological & hydrological process relating to the water resources shortage and environmental change falls into the realm of water science engineering. Northern China, where agriculture accounts for 80% of total water consumption, suffers from the most serious water shortage. The essential theory concerning measures for effective agricultural water conservation and regional water resources regulation is based upon how to develop the “five waters” circulation mechanism through developing plant-coupling ecological regulation on the basis of the conventional “four waters” (namely, rainfall - surface water - soil water - ground water) conversion mechanism.
The water resources evolution laws which are directly related to the water circulation basis in the river basin have become a worldwide core issue in the water resources planning of hydraulic projects and water resources sustainability. The Yellow River is the second largest exoreic river in China, and it is nicknamed as “the Mother River” in China. Nevertheless, since the 1990s, it has experienced eight consecutive years of flow cutoff. The water resources crisis has directly affected the national economy and the people’s livelihood, receiving attention from all over the world. In 1999, China initiated the “973” key fundamental project - “Water Resources Evolution Rules and Renewability Mechanism in the Yellow River Basin”, and other key research programs funded by the National Natural Science Foundation. Internationally, a hydrological water resources research program regarding the basic mechanisms of hydraulic engineering has been implemented, including such researches as the Non-Linear Process Affected by Global Climate Change and Human Activities, the Prediction in Ungauged Basins (PUBs), and the World Water Assessment Program (WWAP), etc. The study of the water circulation mechanism and water resources evolution laws in river basins is one important challenge that attracts worldwide attention.