Bonn · Like most years this century, 2018 was also warmer than normal. It was actually the warmest year since weather records began in Bonn in 1895, as can be seen from look at data from the University of Bonn’s Endenich weather station and weather history.
Temperature: Another year that was too warm and this time very sunny– these are the characteristics of last year in brief. The annual average was 12.9 degrees, which is 2.6 degrees more than the long-term average. Previously the warmest year was 2014 with an average temperature of 12.6 degrees. The coldest year of the last 123 years was 1940 with an average of 8.3 degrees.
Only February and March 2018 were cooler than normal. They lagged up to two degrees behind their target. All other months were warmer than normal. The highest positive deviations this time were in July, which was 4.5 degrees above its long-term average. April and May were the warmest months since 1895.
Hottest day was 7 August
The hottest day was 7 August, when Bonners had to sweat through temperatures of 39.1 degrees during the afternoon. On 28 February, the lowest temperature of minus 8.2 degrees was measured. The extreme temperatures of the last 123 years were registered at 39.2 degrees on 12 August 2003 and minus 23.8 degrees on 27 January 1942.
The mercury index rose to over 30 degrees on 31 days (2017: 15) and there were 99 (57) summer days of more than 25 degrees in the shade. On the other hand, there were 39 (24) frosty days with a minimum temperature under zero degrees. There were two ice days (maximum temperature under zero degrees) in 2018, against three in 2017. There were six tropical nights (minimum 20 degrees), the same number as last year.
Sun: it shone for a total of 2003 hours, 395 hours more than last year. This means second place in 49 years of observation. The sun shone for 461 hours longer than its long-term average. Only January and December failed to reach the monthly target. The gloomiest month of the year was January, which only reached 66 per cent of its target. The sun shone for the longest in July with 320 hours.
Rainfall: after the many wet years since 2003, the heavens opened in a more restrained manner last year. A total of 602.7 litres of rain per square metre (last year 801.4 litres) fell on 151 (186) days – seven per cent less than the long-term average. Only January (164 per cent), March (122 per cent), June (134 per cent) and December (180 per cent) were too wet. By contrast, the months of July to November were very dry, which led to a Rhine level of only 0.79 metres at the end of October – the second lowest level since 1901.
The highest daily level last year was measured at 43.4 litres per square metre on 18 August. What is especially noticeable is that the number of heavy rain days is increasing. Whereas 18 days were recorded on which more than ten litres of rain per square metre fell in 2012, the number of heavy rain days rose to 25 in 2014 and 28 in 2016. However, last year there were only 14 days.
Original text: Klaus Kosack. Translation: kc