LONG-TERM PERSPECTIVE ON THE NATURE OF THE AIR-WATER TEMPERATURE RELATIONSHIP - A CASE-STUDY

Monthly mean data from a 90 year period relating to a small catchment (1424 . km(2)) in north-central Austria were used to provide a long-te rm perspective on the nature of the air-water temperature relationship . Annual mean values of air and water temperature were related in a re latively insensitive and scattered way (r(2) < 55%, b < 0 . 65), where as the relationship for monthly mean values was closer and steeper (r( 2) > 95%, b > 0 . 65). A separate regression equation was needed to de scribe the behaviour of monthly mean water temperatures as the air tem peratures fell below freezing. Analysis of air-water temperature regre ssions for individual months revealed a series of relations which were generally more scattered and less, but variously, sensitive than the ensemble relationship of monthly mean values. Monthly mean water tempe ratures could be predicted from the ensemble air-water temperature rel ationship and from the relations for individual months with root mean square errors of > 1 . 0 and < 0 . 8 degrees C, respectively. Segmenta tion of air-water temperature regressions according to air temperature s above and below freezing did not significantly improve water tempera ture prediction. Hysteresis in, and the relatively low slope of, the a ir-water temperature relationships in the study catchment reflected th e importance of snowmelt in the flow regime.