The likelihood of holding outdoor skating marathons in the Netherlands

Chance of holding the Frisian Eleven-City Ice-Skating Marathon diminishes further

Chance of holding Elfstedentocht appealing climate-change indicator

This publication reflects the latest information on the development of the climate-change indicator ‘Chance of holding an Elfstedentocht’. The Netherlands Environmental Assessment Agency first published the indicator in 2005 and subsequently included it in the Environmental Balance 2005. This indicator has been developed especially to illustrate the consequences of climate change in a way that is particularly appealing to a Dutch audience. The article in Climatic Change is the first publication in which the indicator has been updated to include the data for the most recent winters (2006-2007 and 2007-2008).

Assessing uncertainty

For a variety of reasons the indicator ‘Chances of holding an Elfstedentocht’ is more complex than other indicators for climate change, such as temperature or precipitation data. The chances of holding an Elfstedentocht depend on:

• The maximal ice thickness: the Elfstedentocht is only organised when ice thicknesses exceed 15 cm along the entire route.
• The amount of open water due to drainage, or flowing under bridges.
• Organisational factors, such as creating facilities for ‘kluning’ (walking on skates) and mobilising competitive and non-competitive skaters.

The uncertainties surrounding this indicator are large. The best estimate for 2008 is once every 18 years, but the lower limit is once every 7 years and the upper limit is once every 64 years. Still, the conclusion that the chances are diminishing, over time, is robust.

Four opportunities for an Elfstedentocht in the 20th century

Calculations from the Netherlands Environmental Assessment Agency show that, over the previous century, the Elfstedentocht could have been − but was not − organised in 1939, 1979, 1987 and 1996. The reasons for not holding an Elfstedentocht in those years, vary.

Future chances of holding an Elfstedentocht are expected to diminish further

In an addendum to the Climatic Change article the Netherlands Environmental Assessment Agency is also publishing projections for 2050. It appears that in that year, in different climate scenarios by the Royal Netherlands Meteorological Institute, the chances of holding an Elfstedentocht would lie between once every 18 years (the most favourable case) and once every 180 years (the most unfavourable case).

• to addendum