# Spatio-Temporal Variability of Water Temperature of Arctic Rivers in Russia over the Past 60 Years
## 3 Results  
### Factors Govering River Water Temperature  
The water temperatures in the rivers of the Russian Arctic are controlled primarily by ambient air temperature. Comparing the monthly means of air and water temperature (1961-2021) yielded [PERSON]'s rank correlation coefficients of r \(>\) 0.7 (n = 11-61, mean 48) for more than 65% of all gauging stations for the months from May to September. For the month of October, such a strong correlation is only found at 40% of all considered gauging stations, which is explained by the beginning of ice formation in this month in the Arctic part of Siberia and the northeast of Russia. The highest correlations (r \(>\) 0.8) are found in rivers of the Onega, Northern Dvina, and Mezen basins, as well as in a number of Arctic Siberian rivers, mainly flowing south of the Arctic Circle and north of 60\({}^{\circ}\) N. In rivers of the European part of the studying area a close relationship between water and air temperature was found for all warm months (May-October), while, in Siberia, the number and location of gauging stations showing a similar close linear relationship varies from month to month (Figure 2). The largest number of gauging stations with a very strong air-water temperature correlation (r \(>\) 0.7) is found for the summer months June to August and is particularly pronounced in July and August. During these months, the rivers of the EPR mainly show low-flow conditions, making it easier to warm lesser volumes of slower flowing water. This is different in the Arctic parts of Siberia and in the northeast of the study area where rivers are affected by spring flood recession and rainfall-induced floods. The correlation coefficients between hydrological data and meteorological data from reanalysis are similar to those derived from the data from meteorological stations. A further analysis of 46 catchment areas of large and medium-sized rivers in the Arctic part of West Siberia and in the north of the EPR showed that the closest relationship (r \(>\) 0.7) between mean air temperature of a catchment area (reanalysis data) and water temperature at gauging stations occurs in May, at the beginning of the spring floods, when water temperatures start to rise again, and in September and October, during autumn floods, when water temperatures drop significantly. Strong correlations of mean catchment air temperature and river water temperature are confined to medium-sized (catchment area from 2000 to 50,000 km\({}^{2}\)) rivers, mainly in the north of the European part of Russia hydrographic region, in the latitudinal zone of 60\({}^{\circ}\)-63\({}^{\circ}\) N.  
An influence of precipitation on river water temperature could not be detected based on monthly averages. This also applies to water flow for which no consistent relation with water temperature was found (Table 1). However, in three separate sections of the upper, mountainous part of the Kolyma River basin, and on some tributaries of the Olenek River, there was a fairly close relationship between water temperature and runoff in some summer months. This, considering the number of hydrological stations under consideration, suggests a high influence of local geographical factors on the river's flow. Meanwhile, in May, in some cases in June (depending on the time of flood passage), and in October, a close relationship between water temperature and river heat flux (r \(>\) 0.7) was observed in the lower sections of big rivers before flowing into the seas of the Arctic Ocean. The strongest influence of the associated heat flux on the extent of sea ice cover in the coastal zone is observed at the beginning of the warm season [2]. In May and June, the correlation between water temperature and heat flux (see Equation (1)) is positive, while from June to September, it is predominantly negative.