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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. [ABSTRACT FROM AUTHOR]

The study describes the trends of monthly mean water temperature (from May to October) and the annual maximum water temperature of the rivers in Latvia during the time period from 1945 to 2000. The results demonstrated that the mean water temperatures during the monitoring period from May to October were higher in the largest rivers (from 13.6 °C to 16.1 °C) compared to those in the smallest rivers (from 11.5 °C to 15.7 °C). Similar patterns were seen for the maximum water temperature: in large rivers from 22.9 °C to 25.7 °C, and in small rivers from 20.8 °C to 25.8 °C. Generally, lower water temperatures occurred in rivers with a high groundwater inflow rate, for example, in rivers of the Gauja basin, in particular, in the Amata River. Mann-Kendall test results demonstrated that during the monitoring period from May to October, mean water temperatures had a positive trend. However, the annual maximum temperature had a negative trend. [ABSTRACT FROM AUTHOR]

Changes in the hydrological regime of the lakes of Latvia depend on natural and anthropogenic causes. This publication summarises the results of the research on the long-term changes in the water level, thermal and ice regimes in the seven largest lakes of Latvia: Liepājas, Usma, Ķıšezers, Burtnieks, Rāzna, Sventes and Lielais Ludzas, and their regional specifics from 1926 to 2002. For most of the studied lakes, the water level has been regulated, except for the lakes Liepājas, Burtnieks and Ķıšezers. Global climate warming has caused considerable changes in the hydrological regime of the lakes during the last decades and the surface water temperature has increased. At the same time, the number of days with ice cover and the thickness of ice have decreased. A positive trend in the freezing date and a statistically significant negative trend for the ice break-up date was found for all lakes. The lakes Liepājas and Usma are located in the western part and Lake Kıšezers in the central part, therefore their hydrological regime, in particular, the thermal and ice regime, differs from the lakes Burtnieks, Rāznas, Sventes and Lielais Ludzas which are located in the northern and southeastern part of Latvia. [ABSTRACT FROM AUTHOR]

This study investigated long-term variability and trends in Latvia's annual, seasonal, monthly and daily precipitation using data from 10 meteorological stations for the period 1925-2006 and from station Riga University for the period 1850-2006. The obtained results indicate that during the 20th century a significant increase in precipitation has occurred in the cold season while the warm period showed a decreasing tendency. The annual precipitation totals showed a slight decrease, at half of the studied stations, due to opposite tendencies in cold season and warm season. The long-term trend in the annual precipitation in Riga (from 1850) was positive with large interannual and interdecadal variability. The extreme precipitation events were evaluated using a set of nine climate change indices, Of these, number of wet days, 1-day and 5-days maximum precipitation, moderate wet days and very wet days showed a well pronounced positive tendency in the cold period of the year particularly in winter. No overall long-term trend was detected in extreme precipitation in summer. As in the case of 150-year precipitation pattern, extreme precipitation exhibited cyclic fluctuations that were more pronounced than linear changes. The close correlation between North Atlantic oscillation (NAO) and extreme precipitation was found for winter season. [ABSTRACT FROM AUTHOR]

Abstract: There is currently a critical knowledge gap in how eutrophication and climate variables separately and interactively impact the dynamics of marine ecosystems. Based on long-term monitoring data we quantified the separate and combined impacts of nutrient loading, temperature, salinity, and wind conditions on zooplankton, zoobenthos and fish inhabiting a brackish water ecosystem in the Gulf of Riga. Changes in zoobenthos communities and herring stock were largely explained by climate variables. Zooplankton species were related to both eutrophication and climate variables, and models combining all environmental variables explained additional variation in zooplankton data compared to the separate models of climate and eutrophication. This suggests that zoobenthos communities and herring stock are largely driven by weather conditions, whereas the combined effect of weather and nutrient loads are likely the cause for dynamic zooplankton communities in the Gulf of Riga. [Copyright &y& Elsevier]

The changes of the chemical composition in Latvian inland waters over the last twenty years were determined, based on data of the National Monitoring Programme. Relationships between the water composition were studied. The chemical composition and seasonal change pattern depend a lot on hydrological factors which differed between eastern and western Latvia. Different pattern of long-term changes is found for substances which have different sources and sinks, at first for nutrients (decrease only in the last few years) and inorganic ingredients (commonly increasing trend). An attempt was made to identify the main sources of the major water ingredients and link changes of their concentrations with changes in loading to waters. [ABSTRACT FROM AUTHOR]