Correlations of Minnesota Stream Water Temperatures with Air Temperatures

Air temperatures are sometimes used as substitutes for stream temperatures. To examine the errors associated with this substitution, linear relationships between 43 Minnesota stream water temperature records and associated air temperature records were analyzed. Weather monitoring stations were, on average, 23.3 miles from the stream stations. From the lumped data set (38,082 data pairs), the general equations, Tw=4.4+0.81Ta, Tw= 1. 9+0. 97 Ta., Tw=0.7+1.04Ta, and Tw=3.3+0.89Ta ,with temperatures in °e, were derived for daily, weekly, monthly, and yearly mean temperatures, respectively. Standard deviations between all measured and predicted water temperatures were 3.soe (daily), 2.6°e (weekly), 1.9°e (monthly), and 1.3°e (yearly). Separate analyses for each specific stream gave lower standard deviations. The measured water temperatures follow the annual air temperature cycle closely. No time lags were taken into account, and periods of ice cover were excluded from the analysis.National Agricultural Water Quality Laboratory, US Department of Agricultur