Long-term changes of the ice regime of rivers in Latvia

The ice regime of rivers is considered a sensitive indicator of climate change. This paper summarises the results of research on the long-term changes in the ice regime parameters under changing climate conditions and their regional peculiarities in Latvia from 1945 to 2012. The ice cover duration on Latvian rivers has decreased during recent decades. The research results demonstrated that there is a positive trend as regards the formation of the ice cover and in 31.8% of the cases the trend is statistically significant at p < 0.05. As regards the breaking up of ice, there is a statistically significant negative trend in 93.2% of the cases at p < 0.05. This indicates an earlier ice break-up date, which in turn, displays a strong correlation with the increase of the air temperature. The same pattern applies to the reduction of the length of ice cover (a statistically significant trend in 86.4% of the cases at p < 0.05). In approximately 60% of the cases, there is a statistically significant reduction of the ice thickness. The estimated winter severity index indicates warmer winters over the last 20 years as well as regional differences in the west–east direction.