This paper examines the relationships between river water temperature, air temperature and stream flow measured continuously for one year at four sites along the main stream of the river Tees in northern England. Maximum and minimum river temperatures were found to correlate fairly closely with equivalent air temperatures at each site, but some emphasis was placed on the effects of hydrological factors on water temperature variations within the 818 km2 basin. The range of water temperature fluctuations was shown to increase upstream and the highest river maxima were also recorded in the upper reaches of the river, owing to the relatively low volume of discharge. On a shorter time scale, stream flow was also found to exert an important influence on river temperature during snowmelt and peak flow events arising from storm rainfall. A multiple regression analysis indicated that air temperature and stream flow together accounted for up to 85 % of the variation of daily maximum and minimum river temperatures in summer.

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