On hydrosphere: Its definition, concerns, and challenges [version 2]

The hydrosphere, a concept stemming from geology and geography, is conventionally recognized as a layer of water on the Earth. Despite its frequent mention in literature, systematic studies on this subject are rare yet. Presented in this paper is our recent perspective on the hydrosphere, providing a comprehensive overview of the research focused on the functions of water in global cycling. We defined the hydrosphere as a dynamical system comprising water materials in solid, liquid, or vapor states, which cyclically interact on a global scale, forming a complex network in alignment with the inherent nature of water and its cycling process. The challenges associated with studying the hydrosphere are discussed, emphasizing the significance of understanding its dynamics, topology, and infordynamics. Furthermore, potential approaches to achieve a thorough comprehension of the hydrosphere are discussed.