Spring 2026 in the Ruhr catchment area: a dry April was followed by heavy rain in May

Spring 2026 was only slightly drier than usual in the Ruhr catchment area, with 95 per cent of the long-term average. This was due to a very wet May, when 111 millimetres of rain fell – almost 150 per cent of the usual amount. March, by contrast, was slightly drier than usual at 89 per cent of the average monthly rainfall, whilst April was considerably too dry at just 46 per cent.

It was primarily the wet May that resulted in a comparatively low number of days requiring water releases this spring: Water had to be released from the Ruhrverband’s reservoirs at the Villigst gauge on only twelve days in total to meet the legally prescribed minimum flows; that is 30 per cent fewer days requiring water releases than is usual in a spring. By way of comparison: during the same period in 2025, there had been 48 days requiring water releases at the Villigst gauge, i.e. four times as many as this year.

All three spring months of 2026 were warmer than the respective long-term reference period: March by 1.8 degrees, April by 0.5 degrees and May by 0.8 degrees. For the whole of spring 2026, this results in a deviation of 1.1 degrees from the reference period and ranks as the 8th warmest spring in the Ruhr catchment area since 1881.

A look at the overall reservoir levels: at the start of spring on 1 March, these were almost exactly at the long-term average (a deviation of minus 0.3 per cent), and by the end of spring on 31 May, they were a good 2 per cent above the long-term average. This means that almost 30 million cubic metres more water is stored in the reservoirs than a year ago. Nevertheless, the water stored in the reservoirs must be managed carefully, particularly against the backdrop of increasing extreme weather events – both to meet long periods of high water supply requirements and to mitigate potential flood peaks during heavy rainfall events by keeping space in the reservoirs free as a precautionary measure.