10. Arctic River Water Temperatures and Thermal Regimes

Water temperature has an important impact on many aspects of basin hydrology and ecology. In the northern regions, the investigation of river thermal regimes and their changes over space and time is a challenge due to data limitations. This chapter determines the water temperature regimes and its changes at several locations within the Yukon, Mackenzie River, and Lena watersheds, and examines their relationship with air temperature. Yukon and Mackenzie Rivers have distinct water temperature dynamics. They remain near zero from freeze-up in the fall to ice break-up in the spring, and reach their peak temperature during mid-summer. For the locations examined, peak mean monthly water temperatures ranged from 9 to 15 °C, and mean July air temperatures ranged from 13 to 16 °C. The lags between water and air temperatures ranged from 1 to 40 days. The largest lag was found at the Great Bear River monitoring location, since water temperature at this site is strongly influenced by the heat storage of Great Bear Lake. Tests of three models, i.e., linear regression, logical regression (s-shape), and the physically based air2stream model, show that the air2stream model provided the best results, followed by logical regression. Linear regression gave the poorest result. Model estimates of water temperature from air temperature were slightly improved by the inclusion of discharge data. The water temperature sampling regimes had a considerable effect on model performance; long-term data provide a more robust test of a model. Comparisons of mean monthly water temperatures suggest significant spatial variability and some inconsistency between upstream and downstream sites, mainly due to difference in data collection schemes. Similar to the VIC model, the CHANGE model can simulate large basin water temperature pattern over the arctic regions as a whole. With this capability, it might be possible to reconstruct the water temperature records for the northern rivers without past observations. This review clearly demonstrates the need to improve water temperature monitoring in the northern regions.