STREAM WATER-TEMPERATURE SENSITIVITY TO WEATHER AND BED PARAMETERS

Water temperatures in natural streams can be modeled using as input air temperature, solar radiation, relative humidity, wind speed, cloud cover and barometric pressure in addition to stream geometry, stream flow, and inflow temperature. MNSTREM is an example of such models that use heat-budget components to calculate the heat exchange between stream water and the atmosphere. The MNSTREM model has been expanded to include heat flux between streambed and water. The model is sensitive to each of the weather and streambed parameters to different degrees. Sensitivity coefficients represent the change in stream water temperature resulting from a unit change in each of the model parameters. They are calculated by two methods that give same order of magnitude results. To establish the sensitivity of the model to each parameter the mean and/or the standard deviations of each of the weather and streambed parameters is multiplied by its sensitivity coefficient. The sensitivity analysis gives quantitative evidence that stream water temperature is more sensitive to air temperature and solar radiation than to other weather and bed parameters. It also shows quantitatively that daily-average stream water temperatures are not very sensitive to the streambed thermal conductivity.