Geen diatitel

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On the use of indices to study changes in climate
extremes
EGS-AGU-EUG Joint Assembly Nice, France, 10
April 2003 Albert Klein Tank KNMI, the
Netherlands
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Guide

• How do we define extreme events?
• Extremes in daily precipitation and temperature
  series from weather stations
• Observed trends in Europe, 1946-now
• amplified response of very wet days
• asymmetric warming of cold warm tail

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www.cred.be
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WMO status of global climate in 2002
www.wmo.ch
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www.dwd.de/research/gpcc/
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Day-count indices of extremes
www.knmi.nl/samenw/eca/
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Day-count indices of extremes
www.knmi.nl/samenw/eca/
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Day-count indices of extremes
Relation between relative trend bq/X required for
80 detection probability (5 level) and series
length N for extreme events with average return
period Tret
Klein Tank and Können, J. Climate (accepted)
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Amplified response of very wet days
Linear trends in rainy season, last 50 years
Easterling et al. (BAMS, 2000) in IPCC-TAR
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Precipitation fraction due to very wet days
R95tot
1) Identify very wet days using a site specific
threshold 95th percentile at wet days in the
1961-90 period
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www.knmi.nl/samenw/eca/
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Frich et al. (Clim. Res., 2002) in IPCC-TAR
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Trends 1961-2001
APN 2002 (Della-Marta, Haylock et al.)
www.bom.gov.au/bmrc/csr/apn/
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Caribbean workshop, Jamaica 2001 (Peterson et
al., 2002, JGR)
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Trends in 5-day rainfall total 1961-1990
Africa workshop, Casablanca 2001
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European precipitation trends

• Averaged over Europe, all indices of wet extremes
  saw increases between 1946-1999, although spatial
  trend coherence is low and many station trends
  are not significant
• The index that represents the fraction of the
  annual amount due to very wet days gives a signal
  of disproportionate large changes in the extremes
• IPCC-TAR
• 2 to 4 increase in frequency of heavy events in
  mid- and high latitudes of the NH
• in regions where total precipitation has
  increased ... even more pronounced increases in
  heavy precipitation events

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IPCC-TAR, Ch.2, Folland and Karl
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upper 10-ptile 1961-1990 the year 1996 lower
10-ptile 1961-1990
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upper 10-ptile 1961-1990 the year 1996 lower
10-ptile 1961-1990
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upper 10-ptile 1961-1990 the year 1996 lower
10-ptile 1961-1990
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www.knmi.nl/samenw/eca/
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www.knmi.nl/samenw/eca/
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www.knmi.nl/samenw/eca/
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European temperature trends

• Recent trends (1946-1999) in temperature extremes
  reflect the general warming fewer cold extremes,
  more warm extremes
• Averaged over all stations, the first decades of
  slight cooling saw narrowing of temperature
  distributions, whereas the last decades of strong
  warming saw widening of temperature distributions
• IPCC-TAR
• lengthening of the freeze-free season in most
  mid- and high latitude regions
• reduction in frequency of extreme low monthly
  and seasonal average temperatures and smaller
  increase in frequency of extreme high average
  temperatures

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ECAD website www.knmi.nl/samenw/eca
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• questions?