Exploring and Quantifying River Thermal Response to Heatwaves

Sebastiano Piccolroaz,Annunziato Siviglia,Marco Toffolon,Christopher Robinson

doi:10.3390/w10081098

Abstract

Most of the existing literature on river water temperature focuseds on river thermal sensitivity to long-term trends of climate variables, whereas how river water temperature responds to extreme weather events, such as heatwaves, still requires in-depth analysis. Research in this direction is particularly relevant in that heatwaves are expected to increase in intensity, frequency, and duration in the coming decades, with likely consequences on river thermal regimes and ecology. In this study we analyzed the long-term temperature and streamflow series of 19 Swiss rivers with different hydrological regime (regulated, low-land, and snow-fed), and characterized how concurrent changes in air temperature and streamflow concurred to affect their thermal dynamics. We focused on quantifying the thermal response to the three most significant heatwave events that occurred in Central Europe since 1950 (July–August 2003, July 2006, and July 2015). We found that the thermal response of the analyzed rivers contrasted strongly depending on the river hydrological regime, confirming the behavior observed under typical weather conditions. Low-land rivers were extremely sensitive to heatwaves. In sharp contrast, high-altitude snow-fed rivers and regulated rivers receiving cold water from higher altitude hydropower reservoirs or diversions showed a damped thermal response. The results presented in this study suggest that water resource managers should be aware of the multiple consequences of heatwave events on river water temperature and incorporate expected thermal responses in adaptive management policy. In this respect, additional efforts and dedicated studies are required to deepen our knowledge on how extreme heatwave events can affect river ecosystems.

Highlights

Air Temperature (AT) is generally thought to be one of the main controls of River WaterTemperature (RWT) e.g., [1,2,3,4], motivating its use as a reasonable proxy to describe, through simplified approaches, the physical dynamics that control river thermal regimes e.g., [5,6,7]
Low-land rivers were strongly affected by this extreme event, to the extent that River WaterTemperature (RWT) response was even amplified when compared to AT, with the seasonally averaged daily RWT anomaly being greater than the
The analysis presented here showed the existence of a large-scale regional coherence of RWT in Switzerland when analyzing rivers with the same hydrological regime, despite the analyzed rivers being varied in terms of catchment area, elevation, and orientation

Summary

Introduction

Temperature (RWT) e.g., [1,2,3,4], motivating its use as a reasonable proxy to describe, through simplified approaches, the physical dynamics that control river thermal regimes e.g., [5,6,7]. In some cases a key role is played by streamflow (SF) e.g., [8,9,10,11,12] This aspect becomes relevant when the aim is to predict how water temperature in a river will respond in the future, because projected increases in AT are expected to be compounded with substantial changes in total annual precipitation [13]. Alterations in snowpack accumulation and timing of spring snowmelt will undeniably affect river thermal regimes

Methods

Results

Conclusion