Water temperature

Water temperature of large European rivers and lakes

Note: Annual average water temperature in River Rhine and River Meuse (1911–2010); River Danube (1901–1998), Lake Võrtsjärv (1947–2011), and average water temperature in August in Lake Saimaa, Finland (1924–2011).

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Past trends

The surface water temperatures of major rivers in Europe have increased by 1–3 °C over the last century. For example, the average temperature in the Rhine near Basel has risen by more than 2 °C in the last 50 years (Figure 1) [i]. The temperature of the downstream part of the Rhine increased by 3 °C between 1910 and 2010. Two thirds of the increase at the downstream Rhine is attributed to the increased use of cooling water and one third to the increase in air temperature as a result of climate change [ii]. A similar increase has been observed in the Meuse. The annual average temperature of the Danube increased by around by 1 °C during the last century. Increases in surface water temperature were also found in some large lakes. Lake Võrtsjärv in Estonia had a 0.7 °C increase between 1947 and 2011, and the summer (August) water temperature of Lake Saimaa, Finland increased more than 1 °C over the last century.

Several time series indicate a general trend of increasing water temperature in European rivers and lakes in the range of 0.05 to 0.8 °C per decade [iii]. The surface water temperature of some rivers and lakes in Switzerland has increased by more than 2 °C since 1950 [iv]. In the large lakes in the Alps the water temperature has generally increased by 0.1–0.3 °C per decade: Lake Maggiore and other large Italian lakes [v].

Projections

Lake surface water temperatures are projected to increase further, in parallel with the projected increases in air temperature. The exact amount of warming depends on the magnitude of global warming, on the region, on the season and on lake properties [vi]. Physical modelling studies predict that temperatures will increase more in the upper regions of the water column than in the lower regions, resulting in generally steeper vertical temperature gradients and enhanced thermal stability [vii]. Such increased lake thermal stability was observed both in Switzerland during the mild 2006/2007 winter [viii] and in Italy during the hot 2009 summer [ix].

[i] FOEN, „Indicator Water temperature of surface waters“ Federal Office for the Environment, 2011, http://www.bafu.admin.ch/umwelt/indikatoren/08605/08609/index.html?lang=en.

[ii] A.H.M. Bresser et al., The effects of climate change in the Netherlands (Bilthoven: Netherlands Environment Assessment Agency, 2006), http://www.rivm.nl/bibliotheek/rapporten/773001037.pdf.

[iii] M. Dabrowski, W. Marszelewski, and R. Skowron, „The trends and dependencies between air and water temperatures in lakes in northern Poland from 1961-2000“, Hydrology and Earth System Sciences 8 (2004): 79–87, doi:10.5194/hess-8-79-2004; D.G. George and M.A. Hurley, „The influence of sampling frequency on the detection of long-term change in three lakes in the English Lake District“, Aquatic Ecosystem Health & Management 7 (2004): 1–14, doi:10.1080/14634980490281164; B. Pernaravièiûtë, „The impact of climate change on thermal regime of Lithuanian lakes“, Ekologija 2 (2004): 58–63; Bresser et al., The effects of climate change in the Netherlands.

[iv] BUWAL, Auswirkungen des Hitzesommers 2003 auf die Gewässer (Bern-Ittigen: Bundesamt für Umwelt, Wald and Landschaft: Schriftenreihe Umwelt Nr. 369, 2004); R. E. Hari et al., „Consequences of climatic change for water temperature and brown trout populations in Alpine rivers and streams“, Global Change Biology 12 (2006): 10–26, doi:10.1111/j.1365-2486.2005.001051.x.

[v] W. Ambrosetti and L. Barbanti, „Deep water warming in lakes: an indicator of climate change“, Journal of Limnology 58 (1999): 1–9; D. M. Livingstone, „Impact of secular climate change on the thermal structure of a large temperate central European lake“, Climatic Change 57 (2003): 205–225, doi:10.1023/a:1022119503144; O. Anneville, S. Gammeter, and D. Straile, „Phosphorus decrease and climate variability: mediators of synchrony in phytoplankton changes among European peri-alpine lakes“, Freshwater Biology 50 (2005): 1731–1746, doi:10.1111/j.1365-2427.2005.01429.x; M. T. Dokulil et al., „Twenty years of spatially coherent deepwater warming in lakes across Europe related to the North Atlantic Oscillation“, Limnology and Oceanography 51 (2006): 2787–2793, doi:10.4319/lo.2006.51.6.2787.

[vi] J. M. Malmaeus et al., „Lake phosphorus dynamics and climate warming: A mechanistic model approach“, Ecological Modelling 190 (2006): 1–14, doi:10.1016/j.ecolmodel.2005.03.017; G. George, M. Hurley, and D. Hewitt, „The impact of climate change on the physical characteristics of the larger lakes in the English Lake District“, Freshwater Biology 52 (2007): 1647–1666, doi:10.1111/j.1365-2427.2007.01773.x.

[vii] F. Peeters et al., „Modeling 50 years of historical temperature profiles in a large central European lake“, Limnology and Oceanography 47 (2002): 186–197, doi:10.4319/lo.2002.47.1.0186.

[viii] J. Rempfer et al., „The effect of the exceptionally mild European winter of 2006-2007 on temperature and oxygen profiles in lakes in Switzerland: A foretaste of the future?“, Limnology and Oceanography 55 (2010): 2170–2180, doi:10.4319/lo.2010.55.5.2170.