Catchment Classification and Hydrologic Similarity

TLDR

Hydrology lacks a universally accepted catchment classification system, yet a framework that links landscape form and hydro‑climatic conditions to catchment function while accounting for uncertainty and multi‑scale variability is needed to provide a common language, guide modeling, and constrain predictions in ungauged basins. This article reviews current approaches to defining hydrologic similarity and catchment classification, identifies missing components, and proposes a foundational framework to stimulate further analysis. The authors suggest metrics for form, hydro‑climate, and function, outline requirements for a classification system, and highlight open questions that must be addressed for full implementation.

Abstract

Abstract Hydrology does not yet possess a generally agreed upon catchment classification system. Such a classification framework should provide a mapping of landscape form and hydro‐climatic conditions on catchment function (including partition, storage, and release of water), while explicitly accounting for uncertainty and for variability at multiple temporal and spatial scales. This framework would provide an organizing principle, create a common language, guide modeling and measurement efforts, and provide constraints on predictions in ungauged basins, as well as on estimates of environmental change impacts. In this article, we (i) review existing approaches to define hydrologic similarity and to catchment classification; (ii) discuss outstanding components or characteristics that should be included in a classification scheme; and (iii) provide a basic framework for catchment classification as a starting point for further analysis. Possible metrics to describe form, hydro‐climate, and function are suggested and discussed. We close the discussion with a list of requirements for the classification framework and open questions that require addressing in order to fully implement it. Open questions include: How can we best represent characteristics of form and hydro‐climatic conditions? How does this representation change with spatial and temporal scale? What functions (partition, storage, and release) are relevant at what spatial and temporal scale? At what scale do internal structure and heterogeneity become important and need to be considered?