# Spatio-Temporal Variability of Water Temperature of Arctic Rivers in Russia over the Past 60 Years
## 3 Results
### Intensity and Direction of Changes in Water Temperature  
Since 1961, a continuous, mostly positive trend (Mann-Kendall \(\alpha\) = 0.05) of monthly water temperature has been observed at a significant number of hydrological gauging stations (from 10% to 90% in some months for certain areas). The prevalence of continuous trends during 1961-2021 is lowest in July-August, during the low-flow period. The percentage of hydrological gauging stations with such trends increases west of the Yenisei River. A significant trend in decreasing water temperature has been observed in several locations:  
1. In several rivers, in the upper reaches of the Kolyma, Alazeya, and Indigirka rivers;
2. In isolated cases, in small rivers in the Pur River basin at hydrometric gauges in cities;
3. In a single case, in one of the smaller tributaries of the Vychegda River, north of the EPR (European part of Russia);
4. In another single case, in a river in Karelia;
5. At the Dudinka hydrometric gauge on the Yenisei;
6. In the area of the Yeniseisk city on the Yenisei River;
7. On the Anadyr River, in its middle course. The small number of identified hydrological stations (seven out of two hundred eighty-six) could indicate either a lack of representative sampling at the measurement points, the presence of systematic measurement errors, or the influence of a range of local factors such as river port activity, riverbed modification, or the effects of naleds (aufices). All cases of a negative trend in water temperature (1961-2021) outside the Kolyma River basin occurred during the period from July to September. Within the Kolyma basin, negative trends were mostly seen in May and July. As discussed previously, negative trends in water temperature are likely caused by local factors or measurements errors. The average intensity of change in water temperature for the period 1961-2021 is shown in Table 10, excluding negative trends during the months of May to October in the hydrographic regions of the Russian Arctic. The maximum intensity of temperature rise in water is typical for rivers in the Russian Arctic, particularly small rivers such as the Nadym, Pur, and Taz, as well as rivers in the Yenisei basin that flow north of the Arctic Circle. This applies to all rivers, regardless of their size, during the month of June, which is when water flow is at its highest. The average water temperatures in rivers in the north of Western Siberia during July, with the most significant variations in water temperature, are presented in Figure 7 for various decades starting from 1961. As can be seen in Figure 7, most of the hydrometric gauges under consideration showed a gradual increase in water temperature over the decades. However, in 2015-2016, there were extremely high water temperatures in the rivers (14-16.7 \({}^{\circ}\)C). These events were likely caused by a combination of factors, as the rivers had a normal flow in July 2015 and 2016, and air temperatures were slightly above average, but no significant anomalies were \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Region** & **Month** & **May** & **June** & **July** & **August** & **September** & **October** \\ \hline Northeast & 0.16 & 0.32 & 0.15 & 0.26 & 0.32 & 0.14 \\ \hline Lena & 0.2 & 0.5 & 0.32 & 0.29 & 0.28 & 0.07 \\ \hline Yenisei & 0.24 & 0.68 & 0.48 & 0.5 & 0.4 & 0.31 \\ \hline North of the West Siberia & 0.33 & 0.74 & 0.49 & 0.28 & 0.35 & 0.2 \\ \hline North of the European part of Russia & 0.42 & 0.51 & 0.41 & 0.32 & 0.31 & 0.33 \\ \hline Karelia & 0.46 & 0.33 & 0.29 & 0.21 & 0.31 & 0.32 \\ \hline Kola Peninsula & 0.34 & 0.36 & 0.26 & 0.21 & 0.29 & 0.22 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Mean statistically significant (relative to Mann–Kendall test \(\alpha\) = 0.05) intensity of water temperature increase in rivers of hydrographic regions of the Russian Arctic (based on data from 286 hydrological gauges) in warm (ice-free) months of the year. observed.