Abstract

Intermittent streams represent a substantial part of the worldwide stream network and their occurrence is expected to increase due to climate change. Thus, it is of high relevance to provide detailed information of the temporal and spatial controls of streamflow intermittency to support management decisions. This study presents an event-based analysis of streamflow responses in intermittent streams in a meso-scale catchment with temperate climate. According to the streamflow responses, events were classified into flow or no-flow classes. Response controls like precipitation, soil moisture, and temperature were used as predictors in a random forest model to identify temporal controls of streamflow intermittency at the event-scale. Soil moisture was revealed as the most important predictor in the catchment. However, different patterns of predictor importance were found among the three dominant geologies in the catchment. Streamflow responses in the slate geology were controlled by soil moisture in the shallow and deep soil layers, while streamflow in the marl geology was primarily controlled by the soil moisture in the upper soil layer. Streamflow responses in catchments covering both marls and sandstone were dependent on soil moisture whereas streamflow in the only catchment with pure sandstone geology depended on precipitation characteristics. In both the slate and marl geology, streamflow intermittency also showed a relationship with seasonal fluctuations of soil temperature, probably as a proxy-variable of seasonal changes in evapotranspiration as well as an indicator of freezing conditions.

Highlights

  • The scientific literature contains a variety of terms and definitions to define different degrees of streamflow intermittency including temporary, ephemeral, seasonal and episodic streams, and intermittent rivers, which are all characterised by ceasing flow during certain periods of the year (Uys and O’Keeffe, 1997; Costigan et al, 2016; Datry et al, 2017; Fritz et al 2020). 25 The stream network changes its spatial extent with the wetting and drying of these intermittent reaches

  • Streamflow responses in catchments covering both marls and sandstone were dependent on soil moisture whereas streamflow in the only catchment with pure sandstone geology depended on precipitation characteristics

  • (2) A random forest model was applied for each site to model flow response classes based on the predictors of precipitation characteristics (Pmean, Pmax, Psums and PD), antecedent precipitation indices (7 and 14-day antecedent precipitation index (API)), maximum soil moisture in two soil depths (θ10 and θ50) and minimum soil temperature

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Summary

Introduction

The scientific literature contains a variety of terms and definitions to define different degrees of streamflow intermittency including temporary, ephemeral, seasonal and episodic streams, and intermittent rivers, which are all characterised by ceasing flow during certain periods of the year (Uys and O’Keeffe, 1997; Costigan et al, 2016; Datry et al, 2017; Fritz et al 2020). 25 The stream network changes its spatial extent with the wetting and drying of these intermittent reaches. 25 The stream network changes its spatial extent with the wetting and drying of these intermittent reaches. Perennial reaches are expected to shift to intermittent streamflow as a result of climate change (Reynolds et al, 2015). Management of these transforming perennial reaches and current intermittent streams can adapt if controls of streamflow intermittency are better understood. Climate, geology, soil, topography, and land use were identified as major spatial controls of streamflow intermittency (Olson and Brouillette, 2006; Reynolds et al, 2015; Trancoso et al, 2016; Costigan et al, 2016; 30 Jaeger et al, 2019; Kaplan et al, 2020a).

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