Wetenschappelijk rapport KNMI'06-klimaatscenario's: Climate change scenarios 2006 for the Netherlands

Climate change scenarios for the Netherlands for temperature, precipitation, potential
evaporation and wind for 2050, and for sea level rise for 2050 and 2100 have been
constructed using a range of data sources and techniques. The scenario variables have been
defined after consultation with a number of potential scenario users.
General Circulation Model (GCM) simulations which have become available during the
preparation for the upcoming Fourth Assessment report (AR4) of IPCC have been used to
derive scenarios of sea level change in the eastern North Atlantic basin and wind speed in the
North Sea area. The GCM simulations also were used to span a range of changes in seasonal
mean temperature and precipitation over the Netherlands. It was found that most of this
range could be related to changes in projected global mean temperature and changes in the
strength of seasonal mean western component of the large scale atmospheric flow in the area
around the Netherlands. Therefore, temperature and circulation were used to discriminate
four different scenarios for temperature, precipitation and potential evaporation, by choosing
two different values of global temperature change and two different assumptions about the
circulation response. The construction of the extreme precipitation and temperature values
and the potential evaporation values was carried out using an ensemble of Regional Climate
Model (RCM) simulations and statistical downscaling on observed time series. Additional
scaling and weighting rules were designed to generate RCM sub-ensembles matching the
seasonal mean precipitation range suggested by the GCMs.
The circulation steering parameter has a great impact on the number of precipitation days,
the seasonal mean precipitation, and the intensity of extreme precipitation exceeded once
every 10 years. Also potential evaporation is affected greatly by the assumed circulation
change. Changes of daily mean wind speed exceeded once per year are rather small,
compared to the typical interannual variability of this variable. Sea level change scenarios are
constructed using a combination of GCM output and a literature survey of sea level change
contributions from changes in terrestrial ice masses. For 2100 the scenarios span a range
between 35 and 85 cm.
This report contains a detailed description of the motivation and rationale of the new
KNMI’06 climate scenarios for the Netherlands, and provides a detailed description of the
methodology used for each group of variables. A summary table (Table 8-1) lists all final
scenario values. The last part of the manuscript provides guidelines for the use and
interpretation of the scenario values. Also an index is provided with a justification of the
statements made in a popular brochure on the KNMI’06 climate scenarios.