Studying catchment storm response using event- and pre-event-water volumes as fractions of precipitation rather than discharge

摘要

Catchment response to precipitation is often investigated using two-component isotope-based hydrograph separation, which quantifies the contribution of precipitation (i.e., event water Q(e)) or water from storage (i.e., pre-event water Q(pe)) to total discharge (Q) during storm events. In order to better understand streamflow-generating mechanisms, two-component hydrograph separation studies often seek to relate the event-water fraction Q(e) / Q to storm characteristics or antecedent wetness conditions. However, these relationships may be obscured because the same factors that influence Q e also necessarily influence total discharge Q as well. Here we propose that the fractions of event water and pre-event water relative to total precipitation (Q(e) / P and Q(pe) /P), instead of total discharge, provide useful alternative tools for studying catchment storm responses. These two quantities separate the well-known runoff coefficient (Q/P, i.e., the ratio between total discharge and precipitation volumes over the event timescale) into its contributions from event water and pre-event water. Whereas the runoff coefficient Q / P quantifies how strongly precipitation inputs affect streamflow, the fractions Q(e) / P and Q(pe) /P track the sources of this streamflow response.