Preprints
https://doi.org/10.5194/hess-2021-450
https://doi.org/10.5194/hess-2021-450

  06 Sep 2021

06 Sep 2021

Review status: this preprint is currently under review for the journal HESS.

Regional, multi-decadal analysis reveals that stream temperature increases faster than air temperature

Hanieh Seyedhashemi1,2, Jean-Philippe Vidal1, Jacob S. Diamond1, Dominique Thiéry3, Céline Monteil4, Frédéric Hendrickx4, Anthony Maire4, and Florentina Moatar1 Hanieh Seyedhashemi et al.
  • 1INRAE, UR RiverLy, 5 rue de la Doua CS 20244, 69625 Villeurbanne, France
  • 2EA 6293 GéoHydrosystèmes COntinentaux, Université François-Rabelais de Tours, Parc de Grandmont, 37200 Tours, France
  • 3BRGM, Bureau de Recherches Géologiques et Minières, BP 6009 45060 Orléans Cedex 2, France
  • 4EDF – Recherche et Développement, Laboratoire National d’Hydraulique et Environnement, Chatou, France

Abstract. Stream temperature appears to be increasing globally, but its rate remains poorly constrained due to a paucity of long-term data and difficulty in parsing effects of hydroclimate and landscape variability. Here, we address these issues using the physically-based thermal model T-NET (Temperature-NETwork) coupled with the EROS semi-distributed hydrological model to reconstruct past daily stream temperature and streamflow at the scale of the entire Loire River basin in France (105 km2 with 52278 reaches). Stream temperature increased for almost all reaches in all seasons (mean = +0.38 °C/decade) over the 1963–2019 period. Increases were greatest in spring and summer with a median increase of +0.38 °C (range = +0.11– +0.76 °C) and +0.44 °C (+0.08– +1.02 °C) per decade, respectively. Rates of stream temperature increases were greater than for air temperature across seasons for 50–86 % of reaches. Spring and summer increases were typically the greatest in the southern headwaters (up to +1 °C/decade) and in the largest rivers (Strahler order > 5). Importantly, air temperature and streamflow exerted joint influence on stream temperature trends, where the greatest stream temperature increases were accompanied by similar trends in air temperature (up to +0.71 °C/decade) and the greatest decreases in streamflow (up to −16 %/decade). Indeed, for the majority of reaches, positive stream temperature anomalies exhibited synchrony with positive anomalies in air temperature and negative anomalies in streamflow, highlighting the dual control exerted by these hydroclimatic drivers. Moreover, spring and summer stream temperature, air temperature, and streamflow time series exhibited common change-points occurring in the late 1980s, suggesting a temporal coherence between changes in the hydroclimatic drivers and a rapid stream temperature response. Critically, riparian vegetation shading mitigated stream temperature increases by up to 16 % in smaller streams (i.e., < 30 km from the source). Our results provide strong support for basin-wide increases in stream temperature due to joint effects of rising air temperature and reduced streamflow. We suggest that some of these climate change-induced effects can be mitigated through the restoration and maintenance of riparian forests, and call for continued high-resolution monitoring of stream temperature at large scales.

Hanieh Seyedhashemi et al.

Status: open (until 01 Nov 2021)

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Hanieh Seyedhashemi et al.

Hanieh Seyedhashemi et al.

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Short summary
Stream temperature appears to be increasing globally, but its rate remains poorly constrained due to a paucity of long-term data. Using a thermal model, this study provides a large-scale understanding of the evolution of stream temperature over a long period (1963–2019). This research highlights that air temperature and streamflow can exert joint influence on stream temperature trends, and riparian shading in small mountainous streams may mitigate warming in stream temperatures.