As air temperature is among the major factors impacting the ice regime, the sum of the annual mean and negative air temperatures from 1945 to 2012 was analysed. The research revealed that the annual mean air temperature had increased on average by 1.0–1.2 °C (Figure 2). The results of the Mann–Kendall test also demonstrated statistically significant trends of the air temperature increase in all of the MMS (Table 1).
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Table 1
Mann–Kendall test results regarding the trend of the change in mean air temperature at the MMS over the time period 1945–2012
| MMS | Number of observations | Test value | p-value | Region* |
|---|---|---|---|---|
| Ainaži | 65 | 3.23 | 0.001 | C |
| Alūksne | 66 | 3.59 | 0.0003 | E |
| Bauska | 66 | 3.60 | 0.0003 | C |
| Daugavpils | 65 | 2.53 | 0.01 | E |
| Rīga | 68 | 2.14 | 0.03 | C |
| Gulbene | 66 | 3.83 | 0.0001 | E |
| Jelgava | 67 | 2.84 | 0.005 | C |
| Liepāja | 66 | 3.13 | 0.002 | W |
| Priekuļi | 67 | 4.05 | 0.0001 | C |
| Rēzekne | 61 | 2.80 | 0.01 | E |
| Rūjiena | 67 | 3.85 | 0.0001 | C |
| Stende | 65 | 2.69 | 0.01 | W |
| Zīlāni | 63 | 3.63 | 0.0003 | E |
| MMS | Number of observations | Test value | p-value | Region* |
|---|---|---|---|---|
| Ainaži | 65 | 3.23 | 0.001 | C |
| Alūksne | 66 | 3.59 | 0.0003 | E |
| Bauska | 66 | 3.60 | 0.0003 | C |
| Daugavpils | 65 | 2.53 | 0.01 | E |
| Rīga | 68 | 2.14 | 0.03 | C |
| Gulbene | 66 | 3.83 | 0.0001 | E |
| Jelgava | 67 | 2.84 | 0.005 | C |
| Liepāja | 66 | 3.13 | 0.002 | W |
| Priekuļi | 67 | 4.05 | 0.0001 | C |
| Rēzekne | 61 | 2.80 | 0.01 | E |
| Rūjiena | 67 | 3.85 | 0.0001 | C |
| Stende | 65 | 2.69 | 0.01 | W |
| Zīlāni | 63 | 3.63 | 0.0003 | E |
*Region of Latvia: W, Western; C, Central; E, Eastern.
Figure 2
Annual mean air temperature variability of the time period 1945–2012 in Alūksne, Daugavpils, Jelgava and Liepāja MMS.
Figure 2
Annual mean air temperature variability of the time period 1945–2012 in Alūksne, Daugavpils, Jelgava and Liepāja MMS.