The effect of projected global climate change due to a doubling of
atmoapheric CO2 on water temperatures in five streams in Minnesota is
estimated using a deterministic heat transport model. The model calculates
heat exchange between the atmosphere and the water and is driven by
climate parameters and stream hydrologic parametera. The model is based on
a finite difference solution of the unsteady heat advection-dispersion equation.
An energy balance at the water surface accounts for the effects of air
temperature, solar radiation, relative humidity, cloud cover and wind speed on
the net rate of heat exchange through the water surface. The energy balance
at the bottom of the stream requires modeling of diurnal heat exchange
between water and streambed.
The model was calibrated against detailed measurements to account for
seasonally variable shading and wind sheltering shown to be dependent on leaf
cover of trees on stream banks. Measurements were made in 5 streams at 2
minute intervals over periods of up to 4 weeks. After calibration, accuracies
of hourly and daily water temperature predictions over periods of several
weeks are on the order of 0.2 to 1°C.
The model is sensitive to each of the aforementioned weather parameters
to different degrees. Sensitivity coefficients are calculated by two different
methods which gave same order of magnitude results. The mean and/or the
standard deviation of each of the weather parameters are combined with the
sensitivity coefficients to establish the sensitivity of the model to each
parameter. The sensitivity analysis showed that stream water temperature is
most sensitive to air temperature and solar radiation.
Using climate projections from the GISS (Goddard Institute for Space
Studies), GFDL (Geophysical Fluid Dynamics Laboratory) and OSU (Oregon
State University) Global Circulation Models (GCM's) as input; stream
temperature simulations predict a warming of freely flowing river reaches by
2.4°C to 4.7°C when atmospheric CO2 doubles. In small shaded streams
water temperatures are predicted to rise by an additional 6° C in summer if
trees along stream banks should be lost due to climate change. These
projected water temperature changes have significant consequences for survival
and growth of fishes in different temperature guilds (cold-, cool- and
warmwater fishes). A model developed by the USEPA, relating fish survival
and fish habitat to water temperatures, was applied to make the first
assessment. The simulation results obtained with the complete heat budget
equations are also used to examine simplified water temperature/air
Environmental Research Laboratory, US Environmental Protection Agency
Sinokrot, Bashar; Stefan, Heinz G..
Deterministic Modeling of Stream Water Temperatures: Development and Applications to Climate Change Effects on Fish Habitat.
St. Anthony Falls Hydraulic Laboratory.
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