Hydrological Yearbook of Switzerland 2016
Discharge, water level and water quality of the Swiss water bodies
Summary of the publication «Hydrologisches Jahrbuch der Schweiz 2016»
On average, 2016 was 0.7 degrees Celsius warmer in Switzerland than in the reference period 1981–2010. The highest precipitation levels for the first half of the year since records began were registered in regions on the north side of the Alps. Summer did not arrive until July, but temperatures remained unusually high until well into September. Prolonged high pressure and record drought at the end of the year resulted in extreme snow deficiency in the mountain regions.
Snow and glaciers
Averaged out over the entire winter of 2015/16, snow depths were only normal in Lower Valais and the north-west side of the Alps at altitudes above approximately 1400 metres above sea level. They were below average in the other regions. Following intensive snowfall in May and June 2016, the prospects for Switzerland’s glaciers looked good for a prolonged period. However, the very warm late summer resulted in high glacier melt.
In many areas, the apparent equilibrium in the annual discharge values was the outcome of a mainly wet first half of the year followed by a dry second half. In many catchments, the discharge values for June 2016 exceeded the average June discharge values for the reference period. Wide- spread low discharge values were recorded in the second half of the year, particularly in the months of October and December. In December, when precipitation levels were the lowest for that month since records began in 1964, the discharge in some catchment areas was around one fifth of the usual volume. There was a major flood event on the Alpine Rhine in mid-June.
The strong and persistent precipitation from mid-June in the central and eastern Pre-Alps prompted the strongest rise in the level of Lake Constance recorded since 1999: the water level in June and July exceeded the high water limit without interruption for over 40 days. Extreme low water levels were also recorded in various lakes in 2016. Lake Neuchâtel reached its lowest level ever at the end of the year.
In terms of the monthly maximums, the warm winter resulted in several new monthly maximums being recorded in the early months of the year. High air temperatures in late August and September also resulted in the previous monthly maximums being exceeded at 18 of the FOEN’s monitoring stations.
The low groundwater levels and spring discharges from the dry end of 2015 rose steadily due to the above-average precipitation in the first half of 2016. Increasingly high groundwater levels and spring discharges were observed from April until June. Temperatures in August were above average and it was also very dry on the whole, thus the groundwater levels and spring discharges normalised as a result.
Source: BAFU (Hrsg.) 2017: Hydrologisches Jahrbuch der Schweiz 2016. Bundesamt für Umwelt, Bern. Umwelt-Zustand Nr. 1712: 36 S.