Water is an origin of life, an essential factor for production, and a basis for ecology. Water resources not only relate to flood safety, drinking water safety, and food security, but also to economic, ecological, and national security. The natural water resources system as a giant complicated system has its natural evolution processes within a range of temporal and spatial scales in the environments. However, because of global climate changes and the intense impact of human activities at presentsuch as abnormally changing precipitation-the more water withdrawn from and wastewater discharged into rivers, the more evolution of natural water resources system is disturbed. What is more, water problems have happened frequently in some regions, especially in mega cities (like Beijing), such as serious water shortages, severe water pollution, and deterioration of the water eco