Upper Bounds for Stream Temperatures in the Contiguous United States

Abstract:Continuous temperature measurements at 11 stream sites in small lowland streams of North Zealand, Denmark over a year showed much higher summer temperatures and lower winter temperatures along the course of the stream with artificial lakes than in the stream without lakes. The influence of lakes was even more prominent in the comparisons of colder lake inlets and warmer outlets and led to the decline of cold-water and oxygen-demanding brown trout. Seasonal and daily temperature variations were, as anticipated, dampened by forest cover, groundwater input, input from sewage plants and high downstream discharges. Seasonal variations in daily water temperature could be predicted with high accuracy at all sites by a linear air-water regression model (r 2 : 0Ð903-0Ð947). The predictions improved in all instances (r 2 : 0Ð927-0Ð964) by a non-linear logistic regression according to which water temperatures do not fall below freezing and they increase less steeply than air temperatures at high temperatures because of enhanced heat loss from the stream by evaporation and back radiation. The predictions improved slightly (r 2 : 0Ð933-0Ð969) by a multiple regression model which, in addition to air temperature as the main predictor, included solar radiation at un-shaded sites, relative humidity, precipitation and discharge. Application of the non-linear logistic model for a warming scenario of 4-5°C higher air temperatures in Denmark in 2070-2100 yielded predictions of temperatures rising 1Ð6-3Ð0°C during winter and summer and 4Ð4-6Ð0°C during spring in un-shaded streams with low groundwater input. Groundwater-fed springs are expected to follow the increase of mean air temperatures for the region. Great caution should be exercised in these temperature projections because global and regional climate scenarios remain open to discussion.

Section: Introductionmentioning

confidence: 98%

Temperature in lowland Danish streams: contemporary patterns, empirical models and future scenarios

Pedersen¹,

Sand‐Jensen²

2006

“…25°C). Increases in the moisture-holding capacity of the atmosphere, which promote greater evaporation from the water surface and, in turn, increase evaporative cooling of the water course, together with enhanced back radiation as water temperatures rise, are considered responsible for this effect (Mohseni et al, 1998(Mohseni et al, , 2002. Testing of data from 584 rivers in the USA has demonstrated that a continuous S-shaped curve, based on a non-linear logistic regression function, successfully represented departures of the water-air temperature relationship at both high and low air temperatures.…”

Section: Introductionmentioning

confidence: 99%

Water–air temperature relationships in a Devon river system and the role of flow

Webb¹,

Clack²,

Walling³

2003

311

325

Abstract:The nature of the water-air temperature relationship, and its moderation by discharge, were investigated for catchments ranging in size from 2Ð1 to 601 km 2 in the Exe basin, Devon, UK and for data relating to hourly, daily and weekly time bases. The sensitivity and explanatory power of simple water-air temperature regression models based on hourly data were improved by incorporation of a lag, which increased with catchment size, although relationships became more sensitive and less scattered as the time base of data increased from hourly to weekly mean values. Significant departures from linearity in water-air temperature relationships were evident for hourly, but not for daily mean or weekly mean, data. A clear tendency for relationships between water and air temperatures to be stronger and more sensitive for flows below median levels was apparent, and multiple regression analysis also revealed water temperature to be inversely related to discharge for all catchments and time-scales. However, discharge had a greater impact in accounting for water temperature variation at shorter time-scales and in larger catchments.

“…Continuing concern has focused on the potential impact of global warming on future stream and river temperatures and the ecological implications (e.g. Eaton and Scheller, 1996;Mohseni et al, , 2002Pöckl et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

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

Webb

Zhang

2004

Abstract: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.