Intra-annual variability in the non-advective heat energy budget of Devon streams and rivers

The nature of intra-annual variability in the non-advective heat fluxes affecting streams and rivers in Devon, UK was investigated through detailed monitoring of study reaches in an upland moorland catchment, below a regulating reservoir, and flowing through deciduous woodland and coniferous forest during the period May 1995 to April 1996. A clear pattern of seasonal variation was evident, whereby net radiation provided a heat source during the summer but a heat sink in the winter, as incoming short-wave radiation declined and outgoing long-wave radiation increased. Sensible transfer added heat to the study reaches in the summer but removed it during the winter, and bed conduction acted as a heat sink in the summer period but as a heat source in the winter months. Friction and evaporation added and removed heat, respectively, from the study reaches throughout the year, but the magnitude of these fluxes reflected seasonal variations in discharge and in wind speed. Water temperature generally followed the net non-advective heat energy budget, which was positive in summer but negative in winter. Although a general pattern of seasonal variability in the non-advective heat energy budget was evident, detailed differences in the nature and extent of intra-annual variability were apparent between the study reaches and particularly between forested and non-forested sites. Copyright (C) 2004 John Wiley Sons, Ltd.