Abstract
The dynamics of flood event characteristics, such as the runoff coefficient and the recession time constant, differ in time and space, due to differences in climate, geology, and runoff generation mechanisms. This study examines the variability of event runoff characteristics and relates them to climatic and hydro-geological characteristics available at the regional scale. The main focus is to examine the role of rainfall patterns (i.e., event precipitation volume, precipitation intensity, and antecedent precipitation) and runoff regime (i.e., initial flow before runoff event and event duration) characteristics on the seasonal dynamics of runoff response. The analysis is performed in four small Austrian catchments representing different hydro-geological settings obtained by field mapping. The results are based on an analysis of 982 runoff events identified from hourly measurements of streamflow and precipitation in the period 2002 to 2013. The results show that larger event runoff coefficients and flow peaks are estimated in catchments with high mean annual precipitation than in drier catchments. In contrast to some previous studies, the results show only poor relation between antecedent precipitation (as an index of catchment wetness) and event runoff response. The initial flow is found to be the main factor influencing the magnitude of runoff coefficient and event peaks in all analyzed catchments and geological settings. The recession time constant tends to be inversely related to the maximum event precipitation intensity, with an exception for one catchment (Wimitzbach), which is characterized by the largest proportion of deep interflow contribution to runoff. The analysis of the runoff response by different event types indicates that runoff coefficients and recession time constants are the largest for snowmelt runoff events.
Highlights
Runoff event characteristics are an essential input for hydrologic design, as well as a diagnostic parameter in the hydrological analysis of runoff generation processes and catchment response to rainfall.The event runoff coefficient determines the proportion of rainfall that contributes to direct runoff during a flood event
This study aims to examine the role of climate and runoff regime on the seasonal dynamics of event runoff coefficient, recession time constant, and event peak flow in different geological settings represented by four small catchments in Austria
Previous studies have shown that at the regional scale, the event runoff coefficients are highly correlated with mean annual precipitation, but less related to soil type and land use [1,17]
Summary
The event runoff coefficient determines the proportion of rainfall that contributes to direct runoff during a flood event It reflects the hydrological state of the catchment, and the physiographic catchment characteristics, which are combining into runoff response. Variability and differences in runoff response from plot to small catchment scale were controlled by the connectivity between the ‘infiltrating’ and ‘runoff producing’ areas [10,11]. At this scale, the event runoff coefficients tended to decrease with increasing catchment area, and the recession time constants and runoff peaks were controlled mainly by the land use [3,11,12]. The main controlling factors were attributed to mean annual precipitation and the runoff regime [1], physiographic catchment characteristics [16], and antecedent soil moisture [17,18]
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