Working Towards a More Holistic Set of Hydrologic Principles to Teach Nonhydrologists: Five Simple Concepts Within Catchment Hydrology

Most introductory hydrology textbooks take a reductionist approach to hydrology and break it into distinct processes: precipitation, evaporation, infiltration, groundwater, and open channel hydraulics. Each process is most often quantified with its own standardized set of equations (e.g., the Penman Equation, the Green and Ampt Equation, Darcy's Equation, the Curve Number Equation, and Manning's Equation). This can give the impression (especially to nonhydrologists) that the primary way to answer hydrology‐related questions is to use an equation or link the distinct processes within a hydrologic model. What this reductionist approach overlooks is a more holistic, system understanding of hydrology that can also answer fundamental hydrology questions. This more holistic approach consists of principles well established in the literature but which often have not been recognized as related concepts that should be broadly shared and communicated as foundational concepts in hydrology. This paper lays out five basic concepts that can give broad insight into watershed function without delving into individual hydrologic processes. A wider recognition of these concepts can expand the intuition of those trying to answer hydrologic questions and provide a set of simple analytical tools that do not require extensive modelling. They can provide a foundation for nonhydrologists using hydrology (e.g., aquatic ecologists, geomorphologists, and fishery scientists) to answer questions about flow magnitude, flow variation, or flow forecasting as well as provide a basis to evaluate the outcome of model results. Although this commentary is focused on nonhydrologists, reflecting on these concepts may also help hydrologists work towards integration in a discipline that can often remain fragmented and diverse in its research interests. The application of these concepts requires access to at least some existing stream discharge data as well as meteorological fluxes.