Unseasonable flowering in the Netherlands

Extreme autumn temperatures caused unseasonable flowering in the Netherlands.

The mean autumn temperature in 2006 was 13.6°C, which is 3.4°C above the long-term average.

Observers in the Netherlands reported that more than 240 wild plant species were flowering in December, along with more than 200 cultivated species.

According to biologist Arnold van Vliet of Wageningen University, this unseasonable flowering is being caused by extremely high autumn temperatures.

It was even 1.6°C warmer than in 2005, which was previously the warmest autumn since 1706, when records were first kept. It is very likely that other European countries also experienced unseasonable flowering due to the high temperatures.

This information emerged from a unique, large-scale observation campaign conducted by volunteers during the first 15 days of the month.

The flowering observation campaign was coordinated by the Dutch phenological network Natuurkalender (Nature’s Calendar), which comprises organisations such as Wageningen University, the FLORON Foundation and the popular nature and wildlife radio programme Vroege Vogels (Early Birds).

After the radio programme requested its listeners to make observations of plants in flower on the 10th of December, nearly 2000 observations were submitted by 280 volunteers via the Nature’s Calendar website.

The aim of the observation campaign was to determine the effects of the extreme weather conditions in the Netherlands during the second half of 2006. This year included not only the warmest July and September on record, but also the wettest August.

Temperatures were far above normal: 3.7°C higher in September, 3.3°C higher in October and 3°C higher in November. The first 17 days of December were even more extreme, registering 4.2°C above normal.

For the entire autumn the average temperature was 3.4°C above the long-term average and even 1.6°C warmer than the autumn of 2005, which was previously the warmest on record in the Netherlands.