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KNMI Climate Scenarios
WB21 versus KNMI'06
01-09-2008
Table 2 compares the WB21 scenario values for 2050 with the KNMI'06 values.
Differences
- For the KNMI'06 scenarios both the global temperature rise and the changes in air circulation patterns are used to define the scenarios. For the WB21 scenarios only the global temperature rise was chosen. An unchanged atmospheric circulation was assumed.
- In formulating the KNMI'06 scenarios, recent results from a large number of climate models have been analysed. During the construction of the WB21 scenarios only the results of a limited number of climate models were available. Those only gave good information on global warming and sea level rise. The change in precipitation in the Netherlands in these scenarios was estimated using the statistic relation between precipitation and temperature in historic observational series. It was assumed that this relation would not change in the future and neither the air circulation patterns. With the new analyses the relation between global warming, changes in air circulation above Western Europe and climate change in the Netherlands was mapped systematically. For the first time this was done by combining results from a large number of global and regional climate models and observational series.
- The WB21 'low' scenario has been dropped. The global temperature rise for this scenario is below the likely range of the IPCC 2007 report. In addition, the observed global temperature rise since 1990 makes that this 'low' scenario is very unlikely.
- The WB21 scenarios assume that the temperature rise in the Netherlands is equal to the global temperature rise. This is different from the KNMI'06 scenarios, in which the local temperature rise is obtained by downscaling the regional projections using regional climate model simulations. In particular, for the + scenarios with changes in air circulation is the temperature rise in the Netherlands higher than the global value.
- The increase in heavy winter precipitation in the KNMI'06 scenarios is lower than in the WB21 scenarios.
- The WB21 scenarios provided relative sea level rise (including subsidence). However, the observed subsidence in the Netherlands over the twentieth century has shown large differences over the country (between 0 and 40 cm), which implies that an average value is not very useful.
Similarities
- The use of IPCC projections for global temperature rise is similar. Both in the old 'central' scenario as in the new G and G+ scenarios the global temperature rise is +2°C in 2100 (or +1°C in 2050) compared with 1990. For the old 'high' scenario and the new W and W+ scenarios the global temperature rise is +4°C in 2100 (or +2°C in 2050).
- The reference year is 1990 for both the old and new scenario generation.
Table 2 Comparison between WB21 and KNMI'06 scenario values for 2050. The values in the column 'high dry' WB21* are used for the 'National drought study' that followed WB21 (see ...).
| Variable |
'low'
WB21 |
'middle'
WB21 |
G
'06 |
'high'
WB21 |
W
'06 |
'high dry'
WB21* |
G+
'06 |
W+
'06 |
| Temperature (°C) |
|
|
|
|
|
|
|
|
| Mean winter (DJF) |
+0,5 |
+1 |
+0,9 |
+2 |
+1,8 |
+2,0 |
+1,1 |
+2,3 |
| Mean summer (JJA) |
+0,5 |
+1 |
+0,9 |
+2 |
+1,7 |
+3,1 |
+1,4 |
+2,8 |
| Precipitation summer (%) |
|
|
|
|
|
|
|
|
| Mean (summer half) |
+0,5 |
+1 |
|
+2 |
|
|
|
|
| Mean (JJA) |
|
|
+3 |
|
+6 |
-20 |
-10 |
-19 |
| Intensity in showers |
+5 |
+10 |
|
+20 |
|
|
|
|
| daily precipitation sum exceeded once in 10 years (JJA) |
|
|
+13 |
|
+27 |
|
+5 |
+10 |
| wet day frequency (JJA) |
0 |
0 |
-2 |
0 |
-3 |
0 |
-10 |
-19 |
| Precipitation winter (%) |
|
|
|
|
|
|
|
|
| Mean (winter half) |
+3 |
+6 |
|
+12 |
|
|
|
|
| Mean (DJF) |
|
|
+4 |
|
+7 |
+13 |
+7 |
+14 |
| 10-day sum (winter half) |
+5 |
+10 |
|
+20 |
|
|
|
|
| 10-day sum exceeded once in 10 years (DJF) |
|
|
+4 |
|
+8 |
|
+6 |
+12 |
| Wet day frequency (DJF) |
0 |
0 |
0 |
0 |
0 |
0 |
+1 |
+2 |
| Potential evapotranspiration (%) |
|
|
|
|
|
|
|
|
| Annual |
+2 |
+4 |
|
+8 |
|
+8 |
|
|
| Summer (JJA) |
|
|
+3 |
|
+7 |
+24 |
+8 |
+15 |
| Sea level (cm) |
|
|
|
|
|
|
|
|
| Absolute rise in 2050 |
+5 |
+20 |
+15 - +25 |
+40 |
+20 - +35 |
+40 |
+15 - +25 |
+20 - +35 |
| Absolute rise in 2100 |
+10 |
+50 |
+35 - +60 |
+100 |
+40 - +85 |
+100 |
+35 - +60 |
+40 - +85 |
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