HARP: A suite of parameters to describe the hysteresis of streamflow and water quality constituents

Abstract

Hysteresis occurs in ecological systems when there are internal dynamics that produce variable responses to an external stimuli or stressors. Understanding and quantifying hysteresis is important to inform understanding of system behaviour, support modelling, and provide comparisons within and between systems. We introduce a new tool, HARP (Hysteresis Area, Residual and Peaks) to describe and quantify hysteresis. HARP quantifies the key features of stream discharge–constituent concentration relationships, including the magnitude of the hysteresis (deviation from linearity), phase shifts in the system (end-state deviation from the pre-event state), and the timing of the turning points in the relationship of discharge and concentration. HARP is suitable to use on complex discharge–concentration data, including figure-eight loops, and supports statistical analysis to quantify the characteristics of independent events. The HARP metrics are introduced using discharge–water quality constituent concentration data, but are equally applicable to any system with properties of hysteresis. HARP provides a tool to develop quantitative observations of stream hydrological processes into quantitative enumeration statistics that facilitate comparisons of events and streams.