1 Summer 2003 Deviation from mean Based on ECMWF and ERA-40 Color: temperature anomaly Contours: normalized by standard deviation (Schär et al. 2004, Nature, 427, ) ºC Temperature Anomaly June-August 2003

2 Geopotential Height, 500 hPa Deviation from mean Based on ECMWF and ERA-40 Color: height anomaly Bold contours: anomalies normalized by standard deviation Summer 2003 m Mark Liniger

3 Precipitation Anomaly Deviation from mean Data: GPCC Summer 2003 %

4 Dried-up River Töss (Central Switzerland, August 28,2003)

5 Estimation of Return Periods extremely rare event 10 y 1000 y 100 y mean (Schär et al. 2004, Nature, 427, ) Swiss Temperature Series (mean of 4 stations)

6 Changes in Mean (Katz and Brown 1992, Folland et al. 2001, IPCC, 2001) For extremes far away from mean, “variability is more important than mean” coldwarm coldwarm increase in the frequency of extreme warm conditions increase in the frequency of extreme warm/cold conditions Temperature Frequency versusChanges in Variability

7 Summer Variability in Climate Change Scenarios Atmospheric GCM (HadAM3, ~120 km) Coupled GCM (HadCM3, ~300 km) Greenhouse-Gas Scenario (IPCC SRES A2) Regional Climate Model (RCM) (CHRM / ETH, 56 km) (EU-Project PRUDENCE, NCCR Climate) Time slice experiments CTRL ( ) SCEN ( )

8 SCEN Simulated Summer Temperatures CTRL Simulated: T  = 16.1 ºC  = 0.97 ºC Observed:  = 16.9 ºC  = 0.94 ºC Gridpoint near Zurich  T =4.6 ºC  /  =100% strong increase in variability (Schär et al. 2004, Nature, 427, )

9 [ºC][%] Change in Mean Temperature  TChange in Variability  /  Summer (JJA) (Schär et al. 2004, Nature, 427, )

10 Comparison of T and P anomalies OBS: Swiss Series SIM: CTRL and SCEN. OBS: 2003 Simulations suggest that by the end of the century every second summer is as warm or warmer (and as dry or dryer) than JJA2003 (with respect to ) (Schär et al. 2004, Nature, 427, )