Spatial heterogeneity of water temperature across an alpine river basin

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Abstract
River temperature remains a subject of major worldwide research, yet understanding of multi‐scale thermal variability across river systems is limited. Such studies are necessary to elucidate the relative importance of site‐specific (reach‐scale) versus landscape controls. This article addresses this research need by identifying water temperature variability across an alpine river basin, using high‐resolution (15 min) water column temperature data at 29 sites in the Taillon–Gabiétous basin, French Pyrénées. Thermal patterns were examined in relation to a suite of meteorological (incoming shortwave radiation, air temperature, and precipitation) and basin characteristics (altitude, azimuth, stream length, and stream order). Mean water temperature for the monitoring period varied markedly across the river basin, ranging from 0·4 °C at the Taillon Glacier to 14·6 °C in a south‐facing hillslope groundwater stream. Basin‐scale water temperature patterns were strongly influenced by stream water source. Stream temperature was also significantly associated with basin characteristics, most notably altitude, azimuth, and stream length. Thermal heterogeneity across the basin was higher than that along the Taillon Glacier stream, despite rapid longitudinal warming rates with distance from the glacier snout. The timing of thermal extremes (maximum/minimum) during two contrasting hydrometeorological events (hot summer day vs intense hail/rain storm) revealed a clear synchronicity of thermal response among sites, although notable exceptions included karstic groundwater streams that were weakly influenced by concurrent meteorological conditions. Overall, the study demonstrates high thermal heterogeneity at the basin scale (being equal to, or greater than, that found in previous investigations), and the major effect of water source and landscape factors such as altitude, azimuth, and stream length on alpine stream temperature. Copyright © 2008 John Wiley & Sons, Ltd.

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