Linear Air/Water Temperature Correlations for Streams during Open Water Periods

The linear correlation of air temperatures and stream temperatures was investigated in this paper. Time lag, time scale, and mesoscale air temperature variability influence the magnitude of the regression coefficients of the linear model, as well as the strength of correlation. Monthly and weekly time scales were found to produce the best correlations. Streams affected by impoundments, reservoirs, and/or artificial heat inputs generally limit the air/stream interaction and produce poor correlations. Ground-water inflows, stream shading, and wind sheltering limit the influence of air temperature on stream temperature thereby reducing the slope of the relationship, but do not typically affect the strength of correlation. Air/stream temperature correlations from Minnesota remained linear throughout the extent of air temperatures experienced, whereas air/stream temperature correlations from Oklahoma departed from linearity as air temperatures exceeded approximately 25(degree)C due to evaporative cooling. Linear air/stream temperature correlations will overestimate stream temperatures at extreme air temperatures.