european climate assessment & possible role of the chr ‘workshop and expert meeting on...
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European Climate Assessment& possible role of the CHR
‘Workshop and Expert Meeting on Climatic Changes and their Effect on Hydrology and Water
Management in the Rhine Basin’Ede, 24 June 2003
Albert Klein TankKNMI, the Netherlands
Scope
1. Projections
2. Observations
now
now
indices of extremes observed trends, 1946-now worldwide co-ordination role of CHR
Topics:
WMO status of global climate in 2002
www.wmo.ch
http://www.dwd.de/en/FundE/Klima/KLIS/int/GPCC/GPCC.htm
Elbe flooding: August 2002 rainfall
Temperature
Precipitation
Wijngaard et al., Int. J. of Climatol., 2003
Data quality control and homogeneity
IPCC-TAR, Ch.2, Folland and Karl
Detection of “(a)symmetric warming”
Easterling et al. (BAMS, 2000) in IPCC-TAR
Linear trends in rainy season, last ~50 years
“Amplified” response of very wet days
“Precipitation fraction due to very wet days”
1) Identify very wet days using a site specific threshold = 95th percentile at wet days in the 1961-90 period
2) Determine fraction of total precipitation in each year that is due to these days
3) Trend analysis in series of fractions
Index: R95%tot
www.knmi.nl/samenw/eca/
www.knmi.nl/samenw/eca/
Klein Tank and Können, J. Climate (in press)
Klein Tank and Können, J. Climate (in press)
Frich et al. (Clim. Res., 2002) in IPCC-TAR
European trends 1946-1999
increase per decade in annual precipitation amount: 7.6 (0.7 14.5) mm increase per decade in annual number of wet days: 0.4 (-0.5 1.3)
percentile-threshold indices increase per decade
absolute-threshold indices increase per decade
R75%
R95%
R95%tot
0.4 (0.1 0.7)
0.2 (0.1 0.2)
0.3 (0.1 0.5) %
R10mm
R20mm
RX1day
RX5day
0.3 (0.1 0.5)
0.1 (0.0 0.2)
0.2 (-0.1 0.5) mm
0.6 (0.0 1.2) mm
Klein Tank and Können, J. Climate (in press)
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”
ECA&D website: www.knmi.nl/samenw/eca
CHR and ECA&D
Some examples for the Rhine basin:
Winter season (October–March) trends in:
Highest 5-day precipitation amountTotal precipitationPrecipitation fraction due to very wet days (> 95th ptile)
Summer season (April–September) trends in:
Maximum number of consecutive dry days
www.knmi.nl/samenw/eca/
www.knmi.nl/samenw/eca/
www.knmi.nl/samenw/eca/
www.knmi.nl/samenw/eca/
synop station
102
107
109 104 103
105
106
115
113
110
108112
111
114
66
34
50171849 47
24
1648 12
7
8 6
2
3
1
7675
72
7174
73
100
97
70
69
68
96
92
67 6564
33
35
3736
93
94
9
10
78
79
80
81
82
84
83
4
5
11
13
1415
19
20
21
22
23
25
28
29
26
27
8886
85
87
32
31
30
45
44
39
38
40
46
51
52
55
5453
56
57
60 62
63
42
41
59
43
61
58
90
9899
101
95
91
77
89
116
117
121
129
130
126
131133
132
118
119
120
128
127
123
124
125
122
134
100 0 100 Kilometer
N
HBV DistrictsErftLahnLippeLower RhineMainMiddle RhineMoselleNaheNeckarRuhrSchweizSiegUpper RhineUpper Rhine 2
GewässerStaatsgrenze
CHR dataset:
Daily series of area-averaged precipitation
CHR dataset
Highest 5-day precipitation amount
winter half (Oct-Mar) 1962-1995
CHR dataset
200019901980197019601950
prec
ipita
tion
amou
nt (
mm
)
100
80
60
40
20
0
100
80
60
40
20
0
Highest 5-day precipitation amount
winter half (Oct-Mar) 1962-1995
CHR dataset
200019901980197019601950
prec
ipita
tion
amou
nt (
mm
)
100
80
60
40
20
0
100
80
60
40
20
0
CHR dataset
Total precipitation
winter half (Oct-Mar) 1962-1995
CHR dataset
200019901980197019601950
prec
ipita
tion
(mm
)
800
600
400
200
0
800
600
400
200
0
CHR dataset
Precipitation fraction due to very wet days (> 95th perc.)
winter half (Oct-Mar) 1962-1995
CHR dataset
200019901980197019601950
perc
enta
ge
40
30
20
10
0
40
30
20
10
0
Precipitation fraction due to very wet days (> 95th perc.)
winter half (Oct-Mar) 1962-1995
CHR dataset
200019901980197019601950
perc
enta
ge
40
30
20
10
0
40
30
20
10
0
CHR dataset
Max. no. of consecutive dry days
summer half (Apr-Sep) 1962-1995
CHR dataset
200019901980197019601950
no.
of d
ays
40
30
20
10
0
40
30
20
10
0
Conclusions
The indices reveal clear changes in precipitation extremes over Europe in the last ~50 years
Need to investigate the causes/underlying mechanisms, e.g. how are observed trends related to variability and change in atmospheric circulation
The examples show that it is interesting to study the ECA indices in more detail for the Rhine Basin, which requires a dense network of daily station series
the end; …questions?
Relation between relative trend bq/X required for 80% detection probability (5% level) and series length Nfor extreme events with average return period Tret
Klein Tank and Können, J. Climate (in press)
21365~ retTXbq
6x
23~ NXbq
3x
Day-count indices of extremes