THE PREDICTION OF WATER TEMPERATURES IN CHALK STREAMS FROM AIR TEMPERATURES

The water temperatures of four English chalk streams which have a large groundwater component in their discharge were studied. Simple linear regression models were used to described mean monthly water temperature as a function of mean monthly air temperature. There were no significant between-year differences within rivers, in the case of the Lambourn, Winterbourne and Tadnoll. For the Frome, only one year out of the eight studied was significantly different from the others. Further analysis revealed that there were no significant differences between the Tadnoll, Winterbourne and Lambourn, and that the relationship between maximum monthly water temperature and air temperature was best described by the equation y = 4.29 + 0.55x. Using this pooled equation to predict river temperatures for the three rivers studied gave mean deviations of less than 1-degrees-C from the observed temperatures. It was concluded that linear regressions of the type presented are sufficiently accurate to predict the thermal regimes of rivers for a variety of limnological purposes. They can also be used to predict the temperature response of chalk streams to increased air temperatures that may be produced by climate change. The results predict that chalk streams would show less increase in temperature than other running waters under these circumstances.