Effect of air temperature upon mean water temperature in streams in the north Pennines and English Lake District

Abstract

SUMMARY. Water temperatures from six north Pennine streams (approximate mean annual discharges 0.04–1.5 m3 s‐1) and two Lake District streams (mean annual discharges c. 0.04 m3 s‐1) were used to examine the possibility of predicting 5‐day or 7‐day mean water temperatures from standard meteorological/hydrological data collected at north Pennine stations. The relationship between mean air temperature (X) and mean water temperature (Y) was approximately linear, except in the Pennine streams for periods when mean air temperature was below 0°C. The calculated regressions of mean water temperature upon mean air temperature accounted for 86–96% of the variance of water temperature even when the air and water temperatures were measured at stations some 50 km apart. A negligible improvement was obtained by the use of multiple regressions incorporating rainfall or stream discharge from a nearby metering weir. Predicted water temperatures were rather lower than observed values during the first half of the calendar year and rather higher during the second half, but these seasonal differences could not be adequately quantified for practical application.