Hydroinformatics is a highly interdisciplinary subject that promotes the fundamental understanding and technology developments of the water cycle in natural system and the built environment in a digital era under uncertainty of global changes. It emphasizes the interactions between natural system from atmosphere to ocean and the built environment via artificial interventions in that cycle such as urban drainage, low impact development, flood and drought management, wastewater treatment, and water supply systems with the aid of sensing, monitoring, modeling, and control technologies. It also provides knowledge via decision science at all levels from governance and policy to management and operations, as well as strives to understand the social decision-making processes by which existing and emerging sensing, information, communication, automation, and control technologies are brought into practical use. While all synergistic applications of the above technologies are highly encouraged for use in addressing the increasingly serious water problems under global change impact, the traditional numerical simulation, optimization and forecasting of water flows and related hydrological and hydraulic processes remain a foundation of hydroinformatics. Topics of integrative informatics and hydrosystems covered by the journal include, but are not limited to, the following areas: Theoretical Innovation in Process Modelling of Hydrosystems: Advancing hydrosystem modelling can help improve the understanding of many water-related processes with synergies in information, communication, automation, and control technologies. These hydrosystem models may include traditional models of computational hydrology and hydraulics or expanded models accounting for hydroenvironmental, hydrogeological, ecohydrological, ecohydraulic or cryospheric complexity.