A review of hydrologic signatures and their applications

Abstract

Hydrologic signatures are quantitative metrics or indices that describe statistical or dynamical properties of hydrologic data series, primarily streamflow. Hydrologic signatures were first used in eco-hydrology to assess alterations in flow regime, and have since seen wide uptake across a variety of hydrological fields. Their applications include extracting biologically relevant attributes of streamflow data, monitoring hydrologic change, analyzing runoff generation processes, defining similarity between watersheds, and calibrating and evaluating hydrologic models. Hydrologic signatures allow us to extract meaningful information about watershed processes from streamflow series, and are therefore seeing increasing use in emerging information-rich areas such as global-scale hydrologic modeling, machine learning, and large-sample hydrology. This overview paper describes the background and development of hydrologic signature theory, reviews hydrologic signature use across a variety of applications, and discusses ongoing hydrologic signature research including current challenges. This article is categorized under: Science of Water > Science of Water K E Y W O R D S flow indices, flow metrics, hydrologic signatures 1 | INTRODUCTION 1.1 | Discovering the information in streamflow data Streamflow timeseries show patterns: flood peaks and low flow periods, daily changes and seasonal cycles. These patterns are examples of information in streamflow data. The information might describe how the stream reacts to changes in weather, or what magnitudes and rates of change of flow are usual for the stream. Streamflow patterns depend on the physical characteristics of the watershed, telling a story about the path of water from precipitation to streamflow. Flow patterns in turn affect the stream's environment, informing us about riparian conditions and habitats. This paper describes how hydrologists use hydrologic signatures to extract this wealth of information from streamflow. 1.2 | What is a hydrologic signature? Hydrologic signatures are quantitative metrics that describe statistical or dynamic properties of streamflow. They are also known as hydrologic metrics, hydrologic indices, or diagnostic signatures. Hydrologic signatures range from simple

Perceptual perplexity and parameter parsimony

“…Classical examples are recession curve analysis and flow duration curves or other hydrological signatures from observed discharges as indicators of storage change or effective volume in headwater catchments. This will, of course, be more informative where those signatures can be most easily be related to particular processes (via recession coefficients or time constants) and can be robust to uncertainties in the observations (Gupta et al, 2008; Di Baldassarre & Montanari, 2009; Wagener et al, 2007; Westerberg & McMillan, 2015; Westerberg et al, 2016; McMillan, 2021).…”

An epistemically uncertain walk through the rather fuzzy subject of observation and model uncertainties1

“…Perhaps, however, given enough observations it might be possible to again define some limits of acceptability without resorting to the strong statistical assumptions of, for example, kriging interpolation that lack any link to how small‐scale heterogeneities interact nonlinearly in producing responses at larger scales. The use of hydrological signatures, for example, might help in this respect in that as summary variables there will be some effect of integrating over uncertainties in the observations (e.g., Coxon et al, 2014; McMillan, 2020). This would, of course, work best if those uncertainties were aleatory rather than epistemic with nonstationary bias in nature.…”

Streamflow indices to identify catchment drivers of hydrograph

“…Hydrologists use data to underpin the hydrologic system by identifying several unique catchment signatures and employ various flow descriptors independent of statistical assumptions yet capable of capturing signals that reflect the basin's long-term unique behavior. Hydrological indices, commonly referred to as hydrologic metrics, hydrologic signatures, or diagnostic signatures, are quantitative flow metrics that characterize statistical or dynamical hydrological data series (McMillan, 2021). Specifically, streamflow indices are flow descriptors derived from discharge time-series data, and a considerable collection of indices are available to aid in the better characterization of hydrological features, ranging from basic statistics like the mean to more sophisticated metrics (Addor et al, 2018;McMillan, 2021).…”

“…Hydrological indices, commonly referred to as hydrologic metrics, hydrologic signatures, or diagnostic signatures, are quantitative flow metrics that characterize statistical or dynamical hydrological data series (McMillan, 2021). Specifically, streamflow indices are flow descriptors derived from discharge time-series data, and a considerable collection of indices are available to aid in the better characterization of hydrological features, ranging from basic statistics like the mean to more sophisticated metrics (Addor et al, 2018;McMillan, 2021). In many cases, daily streamflow records are not permitted for redistribution; however, researchers have computed streamflow indices and made them publicly accessible.…”

“…Hydrological indices are increasingly used in emerging areas such as global-scale hydrologic modeling and largesample hydrology to extract relevant information and compare the different watershed processes (Addor et al, 2017(Addor et al, , 2018McMillan, 2021). These indices offer an indirect way to explore hydrological processes as well as provide insights into hydrologic behavior in catchments where data other than streamflow is restricted and are https://doi.org/10.5194/hess-2021-307 Preprint.…”