A watershed is a basic unit of the land-surface system and also is a system that exchanges material, energy, and information with the external world while remaining relatively closed within a clear boundary, thereby making it the best unit for theory study and practical applications. Watershed science is an Earth system science practiced on a watershed scale and it has developed rapidly over the previous two decades. The goal of watershed science is to understand and predict the behavior of complex watershed systems and support the sustainable development of watersheds. 

Recently, Professors Guodong Cheng and Xin Li at the Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, pointed that watershed science confronts fundamentally methodological challenges. The challenges include, they write in a new study, "the difficulties of understanding complex systems, achieving scale transformation and simulating the co-evolution of the human-nature system."

Therefore, "... approaches together can create a bridge between holism and reductionism and work as a group of operational methods to combine hard and soft integrations and capture all aspects of both natural and human systems will contribute to the maturation of watershed science and to a methodology that can be used throughout land-surface systems science", they state in an article published in the Beijing-based journal Science China: Earth Sciences.

The goal of watershed science is to understand and predict the behavior of complex watershed systems and support the sustainable development of watersheds. Firstly, in their new article, Professors Cheng and Li review the concepts and contents from different disciplines' perspectives and then think that watershed science is the best unit for the study of land-surface system science. The water, ecosystem, and human activities within a watershed must be considered as a whole. Secondly, they discuss the research methods of watershed science, which include the self-organized complex system method, the upscaling method dominated by statistical mechanics, Darwinian approaches based on selection and evolutionary principles, hydro-economic and eco-economic methods that emphasize the human-nature system co-evolution, and meta-synthesis for addressing unstructured problems. They state that these methods will contribute to the maturation of watershed science.

Research methods in watershed science will not mature without significant advances in Earth observation technology and information technology. Watershed science requires an integrated platform that incorporates monitoring, modeling and data manipulation. The platform requires a distributed, multiscale, and real-time controlled watershed observation systems. Sensor networks and a variety of footprint-scale observational techniques have provided unprecedented opportunities for watershed observations. And also the platform needs a modeling platform for managing multiple models including the study about water, ecosystem, economy system and so on; At last, the platform asks for a data platform which is capable of managing big data, integrating a large amount of observational and model data and generating new data.

The systematic practice of research methods in watershed science is critical. The Heihe River Basin has been used as an experimental river basin for the integrated study of the watershed and for watershed science in China. "Integrated Study of the Eco-hydrological Processes of the Heihe River Basin" (referred to as the "Heihe Plan"), a major program by the National Natural Science Foundation of China, will help China to advance the study of watershed science to international frontiers based on existing integrated studies of the Heihe River Basin. At present, the Heihe Plan has entered the stage of integrated research. Existing and ongoing exploration and practice of integrated research methods in the Heihe River Basin will substantially enrich the methodologies of watershed science.

At last, authors of the study confidently believe that breakthroughs in the research methods of watershed science will occur in the next ten years. （Phy.org）