Transcript Climate Change and Extreme Rainfall

Dynamical Downscaling of Tropical Cyclones
for the North West
Debbie Abbs
A. Rafter, K. Nguyen, M. Thatcher
Centre for Australian Weather and Climate Research
A partnership between CSIRO and the Bureau of Meteorology
CSIRO Marine and Atmospheric Research
Outline of talk
• Background
• ENSO variability in Australian Region
(Based on Australian Bureau of Meteorology TC dataset)
ENSO years from Kuleshov et al. (2008)
• The Conformal Cubic Atmospheric Model (CCAM)
• Detection scheme
• The model suite
• TCs in CCAM forced with Reanalyses
• Modelled characteristics of ENSO variability
• Modelled trends
• TCs in CCAM climate change simulations
• Impact on:
•
•
•
•
•
Numbers,
Spatial distribution,
Intensity
Longevity,
Genesis and Decay
IOCI3 – Perth 29 August, 2008
ENSO Variability & TCs in the Australian Region (1)
Average annual distribution of
TCs (TC/year)
Impact of ENSO on genesis location
(El Nino – La Nina) (TC/year)
TCs form further south
in La Nina years
IOCI3 – Perth 29 August, 2008
ENSO Variability & TCs in the Australian
Region (2)
Timeseries of TC Frequency Anomaly and Nov-Feb Average SOI/2
15
10
5
0
19
99
19
97
19
95
19
93
19
91
19
89
19
87
19
85
19
83
19
81
19
79
19
77
TC Frequency anomaly
19
75
-5
19
73
19
71
SOI/2, TC Frequency anomaly
•Kuleshov et al. (2008) note
significant correlations
between seasonal TC numbers
and ENSO indices
•ENSO also affects region of
occurrence
SOI/2
-10
-15
Impact of ENSO on occurrence
(El Nino – La Nina) (TCs/year)
-20
Year
Average annual profiles for TC longitude crossings (Obs)
6
El Nino
3
La Nina
2
1
Longitude
IOCI3 – Perth 29 August, 2008
16
5
16
1
15
7
15
3
14
9
14
5
14
1
13
7
13
3
12
9
12
5
12
1
11
7
11
3
0
10
9
TCs occur closer to
the coast in La Nina
years
4
10
5
Number of crossings
5
Introduction
• Purpose of the work
• Examine potential changes in TC behavior in the Australian region
associated with climate change
• Model-based approach:
• Resolution issues: almost all GCMs unable to produce reliable
TCLVs (Tropical Cyclone-Like Vortices) at native resolution (~200
km)
• Method:
• GCM output downscaled to ~60 km over Australia (to ~100 km in
surrounding area) using a stretched-grid global atmospheric model
• TCLV detection scheme to find TCs in model output
• Examine how well model represents existing TC climate
• Analyse impact of climate change
• Downscale most intense TCLVs to 15 km resolution in regional
model  changes in intensity (& rainfall)
IOCI3 – Perth 29 August, 2008
The Conformal Cubic Atmospheric Model (CCAM)
100 km
100 km
65 km spacing
Maps the Earth onto a cube.
Highest resolution on ‘face’ over
Aust – very coarse on opposite side.
IOCI3 – Perth 29 August, 2008
Detection of TCLVs in CCAM using modified
Walsh detection criteria
• a vorticity more negative than -10-5 s-1 (as cyclonic vorticity is
negative in the Southern Hemisphere);
• a closed pressure minimum, taken to be the centre of the storm,
within 250 km from a point satisfying criterion 1;
• the total tropospheric temperature anomalies at 750, 500 and 300
hPa must be greater than zero, signifying that the storm has a
warm core;
• the mean wind speed in the area 500 km × 500 km around the
centre of the storm at 850 hPa must be higher than that at 300 hPa;
• the temperature anomaly at 300 hPa must be at least 0.6°K;
• the maximum 10 m wind speed in the storm at any one time must
be at least 11.5 ms-1;
• there must be rotation, as defined by the wind direction, around
the storm centre;
• genesis can only over the ocean and;
• SST ≥ 26°C
IOCI3 – Perth 29 August, 2008
The Model Suite
• An opportunistic approach – runs weren’t for TC research
• Model testing & development
• Regional climate studies
• A suite of 4 simulations (and growing) nested in reanalyses
•
•
•
•
Does the model adequately represent reality?
NCEP and ERA40,
Different nudging options
Different parameterisations schemes
• A single (but growing number of) climate change simulation
•
•
•
•
Nested in CSIRO Mk3 A2 simulation
Bias-corrected SST
Used to identify climate change impact
Provide initial and boundary conditions for downscaled runs
IOCI3 – Perth 29 August, 2008
How well does the model represent reality?
Reanalysis-based results
IOCI3 – Perth 29 August, 2008
ENSO variability and TCs in CCAM (1)
Not enough TCLVs in CCAM
~ 60% of obs
Occurrence
Spatial characteristics of ENSO on
occurrence and genesis captured but
too weak – especially for genesis.
IOCI3 – Perth 29 August, 2008
Genesis
ENSO variability and TCs in CCAM (2)
Average annual profiles for TC longitude crossings (Ensemble Average)
6
CCAM captures variation in
TC longitude crossings
between El Nino & La Nina
years
Number of crossings
5
4
El Nino
La Nina
3
El Nino(Obs)
La Nina(Obs)
2
1
16
1
15
7
15
3
14
9
14
5
14
1
13
7
13
3
12
9
12
5
12
1
11
7
11
3
10
9
10
5
0
Longitude
Timeseries of TC Frequency Anomaly
8
SOI/2, TC Frequency anomaly
19
71
6
4
2
19
99
19
97
19
95
19
93
19
91
19
89
19
87
19
85
19
83
19
81
19
79
19
77
19
75
-2
19
73
0
-4
CCAM TC freq anom
-6
Obs TC Freq anom
-8
IOCI3 – Perth 29 August, 2008Year
CCAM does not capture the
observed inter-annual variability
of TC numbers in the Aust.
region
Possible trends in the number of most intense (Cat
4&5) TCs – models as a proxy for reality
Annual number of intense TCs (106E-164E)
3.5
y = 0.0154x + 1.0622
R2 = 0.0305
Number of intense TCs
3
2.5
Ensemble Average
2
Indian Ocean Ensemble
Linear (Ensemble Average)
1.5
Linear (Indian Ocean Ensemble)
1
y = 0.0248x + 0.4132
R2 = 0.1586
0.5
19
71
19
73
19
75
19
77
19
79
19
81
19
83
19
85
19
87
19
89
19
91
19
93
19
95
19
97
19
99
0
Year
Harper & Callaghan, 2006
(Cat 3 – 5)
This study
( Cat 4 & 5)
1974-1988
29%
11.5%
1989-1998
41%
18.5%
42% increase
60% increase
Change
IOCI3 – Perth 29 August, 2008
What is the impact of climate change?
Dynamical downscaling
from a GCM
IOCI3 – Perth 29 August, 2008
Tropical Cyclones in CCAM
Observations
Modelled current climate
Cyclone days per year based on an analysis on a 2x2 deg grid
A similar analysis of TCLVs for the 2030 (2010-2050)
and 2070 (2050-2090) climates shows a decrease in the
total number of storm occurrences by approximately
13.5% for 2030 and 30.5% in 2070.
IOCI3 – Perth 29 August, 2008
Where are the decreases?
Increased TC activity off Qld
More TC days due to longer-lived TCs
2030
Decreased TC activity off WA
2070
IOCI3 – Perth 29 August, 2008
Fraction
0.3
0.25
Current
0.2
2030
0.15
Duration and Extent
2070
0.1
0.05
Duration
Tropical Cyclone Duration (Aust)
-35
-30
-25
Genesis
-15
Latitude of Genesis (Aust)
-20
-5
0.45
0.5
0.45
0.4
0.4
0.35
Aust
Northern latitude of bin
0.35
0.25
Fraction
0.2
0.15
0.3
0.3
Fraction
0.25
Current
0.2
2030
0.15
2070
0.25
0.05
0.05
0.05
0
0
144
192
240
288
336
384
432
480
528
576
2030
0.15
0.1
96
Current
0.2
0.1
48
2070
0
-35
-30
-25
Hours
-20
-15
-10
-5
-35
0
Fraction
0.25
0.2
0.15
0.6
0.5
0.5
0.4
0.4
Current
2030
0.2
0.3
240
288
336
384
432
480
528
576
-30
-25
Hours
Tropical Cyclone Duration (Qld)
-15
-10
-5
-35
0
0.1
Current
2030
0.15
2070
0.05
0.05
0
192
240
288
336
384
432
480
Hours
IOCI3 – Perth 29 August, 2008
528
576
0.2
Current
0.15 2030
0.1 2070
0.1
0.05
0
0.3
Fraction
0.15
-10
0.25
0.25
0.2
-15
0.35
0.3
Fraction
0.2
144
-20
Latitude of Decay (Qld)
0.35
0.25
96
-25
Latitude of Genesis (Qld)
Pacific
48
-30
Northern latitude of bin
0.4
0.3
Fraction
-20
Northern latitude of bin
0.35
-5
2070
0
-35
0.4
0
0.1
0
192
-5
2030
0.2
2070
0.1
0
-10
Current
0.1
0.05
-15
Latitude of Decay (WA)
0.6
0.3
-20
Northern latitude of bin
Fraction
Indian
0.3
144
-25
Latitude of Genesis (WA)
0.4
0.35
96
-30
Northern latitude of bin
Tropical Cyclone Duration (WA)
48
Latitude of Decay (Aust)
Decay
0
0.4
0.1
Fraction
-10
0.35
0.3
Fraction
0
0
0
-35
-30
-25
-20
-15
Northern latitude of bin
-10
-5
0
-35
-30
-25
-20
-15
Northern latitude of bin
-10
-5
0
Summary
•ENSO has significant impact on Australian region TCs
• CCAM captures spatial variability but not occurrence
• Model outputs suggest possible increase in number of intense TCs since 1970s
•Decrease in the number of TC days in the Australian region
• Decrease in Indian region – 44% decrease in TC numbers
• Increase in parts of Pacific region – 9% decrease in TC numbers
•More intense TCs in future
• Lower central pressures
• Stronger winds – mainly in the Pacific
•Changes in TCs duration
• Decrease in number of long-lived TCs in Indian
• Increase in number of long-lived TCs in Pacific
•Increase in poleward occurrence
• Poleward shift in latitude of average genesis region
• Pacific storms tending to decay further south – average of 3 deg. Latitude.
• No change in decay region of Indian storms
IOCI3 – Perth 29 August, 2008
CCAM TCLV detection results:
TC numbers and trends
• Fewer storms, less variability
• Decrease in annual average TC
numbers
• Also a decrease in the interannual variability as measured by
the standard deviation
current
2030
2070
Mean
16.0
14.0
11.6
Standard
deviation
5.7
5.0
4.2
Timeseries of TC numbers
35
30
Number of TCs
25
current
20
2030
15
2070
10
5
0
1
3
5
7
9
11
13
15
17
19
21
Year
IOCI3 – Perth 29 August, 2008
23
25
27
29
31
33
35
37
39
CCAM TCLV detection results:
TC numbers and trends
• Fewer storms, less variability
• Decrease in annual average TC
numbers
• Also a decrease in the interannual variability as measured by
the standard deviation
current
2030
2070
Mean
16.0
14.0
11.6
Standard
deviation
5.7
5.0
4.2
Timeseries of TC numbers
35
BUT…
30
Number of TCs
25
current
20
2030
15
2070
10
5
0
1
3
5
7
9
11
13
15
17
19
21
Year
IOCI3 – Perth 29 August, 2008
23
25
27
29
31
33
35
37
39
CCAM TCLV detection results:
Severe TC numbers and trends
current
2030
2070
Mean
4.1
8.7
9.7
Standard
deviation
2.2
3.6
3.7
Indian
Ocean
Intense TCs
33%
67%
88%
• More severe TCs!
• Increase in annual average
intense TC numbers
• Also an increase in the interannual variability of intense TCs
Timeseries of Intense TCs
25
Number of TCs
20
15
current
2030
2070
10
5
0
1
3
5
7
9
11
13
15
17
19
21
Year
IOCI3 – Perth 29 August, 2008
23
25
27
29
31
33
35
37
39
CCAM TCLV detection results:
Regional changes - landfall
• Fewer landfalls in WA; slightly more in QLD
• Average annual latitude crossings – proxy for landfall
• Fewer crossings seen in NW WA region
• Slightly more crossings off QLD
Average Annual Longitude Crossings for Aust TCs
5
4.5
Number of crossings
4
3.5
3
current
2.5
2030
2
2070
1.5
1
0.5
Longitude
IOCI3 – Perth 29 August, 2008
16
3
15
9
15
5
15
1
14
7
14
3
13
9
13
5
13
1
12
7
12
3
11
9
11
5
11
1
10
7
10
3
0
CCAM TCLV detection results:
Regional changes – TC threat
• TCs within 300 km of location (40 year time slices)
• Large decrease in activity near Port Headland
• Fewer storms but longer lasting around Cairns
Port
Hedland
Number
of TCs
TC
days
Cairns
Number
of TCs
TC
days
Obs
55
78
Obs
41
62
current
37
54
current
46
60
2030
31
35
2030
36
57
2070
23
30
2070
31
59
Number
of TCs
TC
days
Mackay
Brisbane
Number
of TCs
TC
days
Obs
26
33
current
22
41
Obs
19
23
2030
18
26
current
6
8
2070
30
47
2030
6
9
2070
9
12
IOCI3 – Perth 29 August, 2008
CCAM TCLV detection results:
Changes in decay location
• More storms decaying off the WA coast instead of over land
• TCs off QLD seem to be decaying further south (main driver for
increases seen in Cairns, Mackay and Brisbane for 2070)
Current climate decay locations
IOCI3 – Perth 29 August, 2008
Changes in decay location - 2070
Continental scale to Regional scale: RAMS
• RAMS
• Regional Atmospheric Modeling Scheme – a high resolution nonhydrostatic model
• 2-way nested grid (45 km and 15 km for these experiments)
• Relocatable – different domain required for each individual storm
modelled
• Event selection for downscaling
• 100 “deepest” storms from three 40-year CCAM climatologies:
• “current”– 1961-2000
• “2030” – 2011-2050
• “2070” – 2051-2090
• Further downscaling to 5 km for most-intense phase of
storm
• Use 15 km outputs
• Downscale ~60 hours at most intense phase
IOCI3 – Perth 29 August, 2008
Setup of RAMS simulations
• Initialising RAMS
• Initialised with CCAM model output from 24 hours prior to first
detection (i.e. genesis) in CCAM
• CCAM output also used for boundary conditions of grid
• TC bogus inserted for first TC detection at 24 hour into RAMS
simulation
• Bogus vortex initialised using minimum central pressure 5hPa deeper
than CCAM pressure, radius to maximum wind of 50 km and radius of
outer closed isobar of 250 km.
• Strong nudging for first 24 hours to TC bogus central pressure for
TC spin-up. Weak nudging for remainder of the simulation.
IOCI3 – Perth 29 August, 2008
RAMS downscaling results:
Minimum track pressure
• Obvious shift
• Distinct shift to deeper pressures in 2070; less clear in 2030 but still
present
• Pressures still not realistically low
Percentage occurrence of Pmin
60
% occurrence
50
40
30
current
2030
2070
20
10
0
940
945
950
955
960
965
970
975
Pmin(hPa)
IOCI3 – Perth 29 August, 2008
980
985
990
995
1000
1005
RAMS downscaling results:
Maximum wind speed
• Not as clear
• Little change from current to 2030
• Shift in PDF by 2070
Percentage occurrence of Vmax
70
60
% occurrence
50
40
current
30
2030
2070
20
10
0
10
15
20
25
30
Windspeed (m/s)
IOCI3 – Perth 29 August, 2008
35
40
45
50
Summary
• Deeper central pressures; less clear impact on wind speeds
• Shift toward deeper pressure storms
• Maximum wind speed does not strongly follow this result
• Fewer storms in total but more frequent severe TCs
• Higher proportion of TCs will be severe, long-lasting storms
• Fewer TC landfalls in WA; slight increase in QLD
• Fewer longitudinal crossings (landfall proxy) in WA region; slightly
more crossings in QLD region
• More TC activity off QLD; less activity off WA
• Fewer TC days off Port Headland; more TC days for Cairns, Mackay
and Brisbane by 2070
• TCs decaying further to the south off QLD; further north off WA
IOCI3 – Perth 29 August, 2008
Debbie Abbs
CMAR/CAWCR
Phone: (03) 9239 4660
Email: [email protected]
Thank you
Contact Us
Phone: 1300 363 400 or +61 3 9545 2176
Email: [email protected] Web: www.csiro.au
Climate change and its impact on extreme rainfall in
SE Australia (Abbs & Rafter)
IOCI3 – Perth 29 August, 2008
Background
IPCC (AR4) & rainfall extremes
• Intensity of rainfall events projected to increase ... even in
areas where mean rainfall decreases (longer periods between
rainfall events) Chap 10 (Global Climate Projections)
• Extremes of daily rainfall very likely to increase, except
possibly in areas of significant decrease in mean rainfall
(southern Australia in winter & spring) Chap 11 (Regional
Climate Projections: Australia – New Zealand)
Recent & current projects (CSIRO +)
• SEQ – NNSW (DCC, Gold Coast City Council)
• Central Coast NSW (DCC, UPRCT, Sydney Metro CMA, Sydney
Water, Southern Rivers CMA, Hunter-Central Rivers CMA
• Vic & lower MDB (DCC, SEACI)
• Fitzroy R. catchment (QDNRM)
IOCI3 – Perth 29 August, 2008
Climate Change projections for rainfall in Australia
•
1.
2.
3.
Projections contain uncertainty due to 3 sources
Climate Sensitivity
Emissions Uncertainty
Spatial Patterns differ amongst different models
IOCI3 – Perth 29 August, 2008
Model Uncertainty – the answer depends on the
model
ARI-100 changes for 2070 from 5 CSIRO climate models
D125
CC-Mk3
CC-Mk2
Mk2-rx1
IOCI3 – Perth 29 August, 2008
Mk3-UK2
Median ARI-5 and ARI-100 change for 2070 from 5
climate models
Most models agree
on increase
Agreement on the
direction of
change from 25
events
Most models agree
on decrease
IOCI3 – Perth 29 August, 2008
Global & Regional Climate Models
•
•
•
•
•
GCMs & RCMs do a good job at simulating global
statistics of temperature-related extremes.
GCMs produce too many days with weak rainfall & too
little rainfall in extreme events.
GCMs & RCMs have coarse spatial resolution & use
parameterizations for unresolved process important for
rainfall (e.g. cloud formation, deep convection).
Not all GCMs & RCMs skilfully simulate the weather that
produces extreme rainfall.
IPCC TAR (2001) recommends improvements to
‘integrated hierarchy’ of GCMs & RCMs
IOCI3 – Perth 29 August, 2008
200 km
Dynamical Downscaling
• Far more realistic
representation of coastal &
terrain effects
• Improved representation of
weather events (e.g. fronts,
TCs, cut-off lows)
65 km
Nesting Structure
Domain
1800km × 1800km
Resolution 22.5km
4 km
Domain
600km × 600km
Resolution 7.5km
IOCI3 – Perth 29 August, 2008
• Better simulation of
ingredients of extreme
events (wind, moisture,
ascent)
• Assumes host GCM
represents observed
statistical characteristics of
main rainfall producing
systems (circulation &
moisture variables)
Value Added by Dynamical Downscaling
Average fractional change in intensity of extreme rainfall
for events of approximately ARI-4 to 40 years
200 km
65 km
4 km
2030
2070
Decrease
in intensity
IOCI3 – Perth 29 August, 2008
Large
increases
in intensity
fraction
Weather systems causing extreme rainfall in
Wollongong – Newcastle region
1
17%
IOCI3 – Perth 29 August, 2008
2&4
2
10%
3
3
24%
5
18%
How well do the models do?
Days corresponding to Extreme Rainfall Types
1980 time slice (40 years)
CSIRO
GCM
Type
NCEP
(av/s.d./total)
UK2
(av/s.d./total)
Mk3.5
(ave/s.d./total)
Mk2
(ave/s.d./total)
1. Tasman High (NE flow)
17 / 5.7 / 686
11 / 5.8 / 461
18 / 5.1 / 729
9 / 3.8 / 347
2+4. East Coast Low
10 / 5.0 / 422
4 / 2.5 / 159
9 / 5.4 / 352
6 / 2.9 / 228
3. Tasman High (E flow)
24 / 7.7 / 976
13 / 4.8 / 523
24 / 7.1 / 966
11 / 4.6 420
5. Bass St High (SE flow)
18 / 6.0 / 730
9 / 3.5 / 366
12 / 3.5 / 486
14 / 5.0 / 551
69 / 15.6 /
2814
38 / 10.7 /
1509
63 / 13.4 /
2533
39 / 10.7 / 1546
Total
Days corresponding to Extreme Rainfall Types
1980 time slice (40 years)
CCAM
Regional
Type
NCEP
(av/s.d./total)
CC-UK2
(av/s.d./total)
CC-M20
(ave/s.d./total)
CC-Mk2
(ave/s.d./total)
1. Tasman High (NE flow)
17 / 5.7 / 686
24 / 7.7 / 974
18 / 5.6 / 706
8 / 3.8 / 302
2+4. East Coast Low
10 / 5.0 / 422
5 / 3.4 / 210
6 / 2.7 / 227
5 / 2.6 / 208
3. Tasman High (E flow)
24 / 7.7 / 976
24 / 6.7 / 978
23 / 6.4 / 939
6 / 4.0 / 302
5. Bass St High (SE flow)
18 / 6.0 / 730
10 / 3.5 / 410
11 / 4.4 / 447
8 / 3.6 / 309
69 / 15.6 /
2814
63 / 14.3 /
2572
58 / 10.0 /
2319
28 / 8.4 / 1121
Total
IOCI3 – Perth 29 August, 2008
Impact on Hi-Res Downscaling – 1-in-100 year events
24 hr rainfall change for 2070
R-CC-Mk2
R-CC-Uk2
R-CC-M20
Challenge: How do we synthesise results to provide meaningful products for
hydrological applications?
IOCI3 – Perth 29 August, 2008
1-in-100 year rainfall events
AR&R (1987, 1997)
Ensemble Average
(a)
IOCI3 – Perth 29 August, 2008
(b)
“Consensus” 2070
ARI-100 2070
Projected changes for 2070
IOCI3 – Perth 29 August, 2008
Products from dynamical downscaling – 30 min to 96
hours, ARI-1 to 100 years
Return period curves
Depth-area curves
Temporal curves
IFD curves
IOCI3 – Perth 29 August, 2008
Applications: Impact of Climate Change on
Flooding
Case Study for Nerang
Catchment
Based on single member
projection.
• Currently 4500 properties are flood
prone - $140M damages
• 20% increase in rainfall → 7000
properties - $235M
IOCI3 – Perth 29 August, 2008
Development of PDFs from Ensemble Members
Projected changes for 24-hr 1-in100 year events – Warragamba
Catchment
Percentage change
R-CC-Mk2
R-CC-M20
IOCI3 – Perth 29 August, 2008
R-CC-UK2
Ens. Av.
Minimum
-49.4
10%
-17.2
25%
7.0
Median:
8.3
Mean
16.1
75%
34.7
90%
61.6
Max
161.0
Summary
Climate change has major implications for the risks posed by severe
weather events. This will be exacerbated by the impacts of population
growth, especially along the east coast of Australia.
• Extreme rainfall is likely to increase in many regions, especially mountainous
regions (SEQ, Sydney Region studies).
• Local interaction of weather with topography important
• Impact greatest for the 2-hr rainfall accumulations & less for the longer durations.
• Extreme rainfall occurring in heavier bursts.
• Tendency for rainfall to begin earlier in 72-hr events
• Impact increases with time – greater at 2070
• PDF’s of changes in rainfall intensity, temporal pattern from downscaled
simulations can be used to perturb historic events to investigate changes in
flood risk
• Outputs are now being used for planning by/for:
Glenelg-Hopkins Catchment Auth.
Gold Coast City Council
Melbourne Water
SEQ Regional Plan
NICCARA
IOCI3 – Perth 29 August, 2008
The Centre for Australian Weather and Climate Research
A partnership between CSIRO and the Bureau of Meteorology
Debbie Abbs
Phone: (03) 9239 4660
Email: [email protected]
Web: www.cawcr.gov.au
Thank you
www.cawcr.gov.au
Thank you
IOCI3 – Perth 29 August, 2008