Changes in global and regional monsoon precipitation projected by

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FOCRAII, Beijing, 8 April 2013
Changes in global and regional monsoon
precipitation projected by CMIP5 models
Akio Kitoh
Kitoh, A., H. Endo, K. Krishna Kumar, I.F.A. Cavalcanti, P. Goswami, T. Zhou, 2013:
Monsoons in a changing world: a regional perspective in a global context.
J. Geophys. Res., 118, doi:10.1002/jgrd.50258.
1
Introduction
Monsoons are responsible for the majority of summer rainfall
within the tropics, where billions of people depend on the
monsoon rainfall. Thus, reliable future projection for
monsoon rainfall, especially on a regional-scale, has been
strongly demanded.
• Provides a latest view of global and regional monsoonal
rainfall changes as projected by CMIP5 multi-models.
• Investigates not only mean precipitation but also some
precipitation extreme indices and monsoon seasonality.
2
Previous studies of the global monsoon
 Historical records
• Decreasing trend in the global land monsoon
precipitation over the last half of the 20th century.
Wand and Ding (2006); Zhou et al. (2008)
• Increasing trend in the combined (oceanic and land)
monsoon precipitation for recent decades (1979-2008)
Wang et al. (2012)
 Future projections
• Increase of global monsoon area and precipitation
intensity.
CMIP3: Hsu et al. (2012)
CMIP5: Lee and Wang (2012). Hsu et al. (2013)
3
CMIP5 model simulations
 Analyzed experiments
• 20th century historical simulations
• 21st century projections under RCP4.5/RCP8.5 scenarios
 Analyzed models
• Monthly output: 29 models
• Daily output:
21 models
4
CMIP5 climate model
5
Global monsoon
Present-day: 1986-2005
Future:
2080-2099
6
Global monsoon domain
• Model mean generally reproduces the observed domain
• Some biases over eastern Asia and the tropical Pacific
: GPCP
: 29 model mean
Monsoon domain: Annual range >= 2.5 mm day-1
Annual range: Difference between MJJAS and NDJFM
(Wang et al., 2011)
7
Global monsoon domain
• Expansion over the central to eastern tropical Pacific,
the southern Indian Ocean, and eastern Asia.
Reduction
Expansion
Monsoon domain:
Period: 2080 to 2099
Annual range >= 2.5 mm day-1
Annual range: Difference between MJJAS and NDJFM
(Wang et al., 2011)
8
Global monsoon precipitation
• Multi-model ensemble matches the observations
• Monsoon-related precipitation will remarkably increase
→ consistent with other studies analyzing CMIP3/CMIP5 models
Historical RCP4.5 RCP8.5
×: GPCP/CMAP
GMA (ratio to the globe)
Large marks: Mean of all models
Change ratio [%]
GMI
by Hsu et al. (2012, 2013); Lee and Wang (2012)
RCP4.5
RCP8.5
GMA
GMI
GMP
GMA: Global monsoon (GM) area
GMP: GM summer total precipitation
GMI: GM intensity (= GMP/GMA)
9
Time series of global land monsoon
Change ratio to 1986-2005 av. [%]
• Decrease from 1950s to 1980s, and increase in the 21st C
• The simulated trend is consistent with the observations
but with less amplitude
Observations
Historical-run
RCP4.5
RCP8.5
20-year running mean
• Thick line:29 model mean
• Shading:29 model spread
(10th-90th percentile)
 Observational data
• CRU-TS3.1
• GPCC-v6
• GPCC-VASClimO
• CMAP
• GPCP
10
Time series of NH/SH land monsoon
Change ratio to 1986-2005 av. [%]
• Large differences in the amplitude between the NH and SH
• Model spread over the SH in the future projections is
larger than that over NH
N. H. land monsoon
S. H. land monsoon
11
Attribution of the decrease in the 20th C
Change rate to 1861-1880 av. [%]
Neither experiments with GHG forcing nor natural forcing
reproduce the decreased trend simulated by the all forcing
→ aerosol effect is essential ?
• Thick line: 14 model mean
• Shading: Inter-model spread (S.D.)
HistoricalGHG: GHG forcing only
HistoricalNat: Natural forcing only
Historical:
All forcing
20-year running mean
14model = “CNRM-CM5 CSIRO-Mk3-6-0 CanESM2 GFDL-CM3 GFDL-ESM2M GISS-E2-H
GISS-E2-R HadGEM2-ES IPSL-CM5A-LR MIROC-ESM-CHEM MIROC-ESM MRI-CGCM3 12
NorESM1-M bcc-csm1-1"
Attribution of the decrease in the 20th C
Change rate to 1861-1880 av. [%]
Land monsoon precipitation in the NH shows larger
response both to the GHG forcing and the all forcing
N. H. land monsoon
S. H. land monsoon
HistoricalGHG: GHG forcing only
HistoricalNat: Natural forcing only
Historical:
All forcing
13
Regional monsoon
Present-day: 1986-2005
Future:
2080-2099
14
Definition of indices (1)
 Mean/extreme precipitation indices
• Pav: Average precipitation
• SDII: Simple precipitation daily intensity index
[mm day-1]
[mm day-1]
 Total precipitation is divided by the wet days
• R5d:
• CDD:
Seasonal maximum 5-day precipitation total
[mm]
Seasonal maximum consecutive dry days
[days]
 Calculated for the summer season.
(MJJAS in NH and NDJFM in SH)
 Calculated over the monsoon domain at the present-day
by each model.
15
Definition of indices (2)
 Monsoon onset/retreat date
(Wang and LinHo, 2002)
• Smooth regionally averaged climatological daily precipitation
using its first 12 harmonics.
• Remove the dry month mean precipitation (January in NH and
July in SH) from it.  Relative climatological precipitation (RCP)
RCP
[mm/day]
JAN. av.
●
5 mm/dy
●
DUR
ONS
RET
16
Validation of the indices
• Mean/extreme precipitation are generally reproduced well
• Monsoon seasonality is more difficult to simulate
Pav: Average precipitation
SDII: Precipitation intensity
R5d: Seasonal maximum of
CDD:
ONS:
RET:
DUR:
5-day precipitation
Seasonal maximum of
consecutive dry days
Onset date
Retreat date
Monsoon duration
× TRMM-3B42
△ GPCP-1DD
(2.0 deg. lat/lon)
17
Future change of the precipitation indices
• Largest increases over the Asian monsoon domains
• Large increases in extremes over America and Africa
[%]
East Asia (EAS)
N. America (NAM)
N. Africa (NAF)
S. Asia (SAS)
S. America(SAM)
S. Africa(SAF)
Australia (AUS)
RCP4.5 RCP8.5
Pav: Average precipitation
SDII: Precipitation intensity
R5d: Seasonal maximum of
5-day precipitation
CDD: Seasonal maximum of
consecutive dry days
18
Future change of the precipitation indices
Change rate of indices in the 50th percentile
19
Change of the monsoon seasonality
Onset: Earlier or not changed
Retreat: Delayed
⇒ longer summer monsoon season
[days]
East Asia (EAS)
Delayed
Earlier
N. America (NAM)
N. Africa (NAF)
S. Asia (SAS)
RCP4.5 RCP8.5
ONS: Onset date
RET: Retreat date
DUR: Monsoon duration
S. America(SAM)
S. Africa(SAF)
Australia (AUS)
20
Attributions of changes in monsoon rainfall
• Enhanced moisture flux conv. due to increased moisture
⇒ increased monsoon rainfall
• However, large differences among the monsoon regions
∆  & − ∆  ∙ 
Anomaly
[10-3 kg m-2 s-1]
Anomaly
[mm day-1]
land monsoon
Future change (RCP8.5)
−∆  ∙ 

land monsoon
−∆  ∙ 

< > LT: Integration in 1000-500hPa
mm day-1
Changes with consensus of more than 75% of models21
Summary
 Global monsoon
• Decreased monsoon rainfall from the 1950s to 1980s
both in observations and simulations.
• Remarkable increase in monsoon precipitation in the
21st century
 Regional monsoon
• Asian monsoon : largest increase both in mean and
heavy precipitation.
• American and African monsoon : large increase in
heavy precipitation, despite modest change in mean
precipitation.
• Longer summer monsoon season in many regions.
22
Thank you !
“Harerun”
mascot of JMA
Reference: Kitoh, A., H. Endo, K. K. Kumar, I. F. A. Cavalcanti, P. Goswami,
and T. Zhou, 2013, Monsoons in a changing world: a regional perspective in
a global context. J. Geophys. Res., doi: 10.1002/jgrd.50258.
23
Attribution of the decreased rainfall in the 20th C
land
NH land
• Thick line: 14 model mean
• Shading: Inter-model spread
(S.D.)
ocean
SH land
HistoricalGHG
HistoricalNat
Historical
24
Change of the monsoon seasonality
[days]
Delayed
Earlier
For calculation of the global mean, the 7 monsoon domain statistics
are averaged with weighting based on their area in the present-day.
25
Attribution of changes in monsoon rainfall
∆ = −∆  ∙  + ∆
[mm/day]
[mm/day]
−∆  ∙ 
[mm/day]

[10-3kg m-2 s-1]
−∆  ∙ 

26
land monsoon
−∆  ∙ 

< > LT: Vertical integration in 1000-500hPa
land monsoon
−∆  ∙ 
< > : Vertical integration in 1000-100hPa
27
Future change (RCP8.5)
∆
MJJAS
∆ = −∆  ∙  + ∆
NDJFM
−∆  ∙ 
∆
• < > : Vertical integration in the troposphere (1000hPa-100hPa)
• Only changes with consensus of more than 75% of models are shown
28
Future change (RCP8.5)
MJJAS
∆
−∆  ∙ 
−∆  ∙ 
∆ = −∆  ∙  + ∆
NDJFM


• < > LT: Vertical integration in the lower troposphere (1000hPa-500hPa)
• Only changes with consensus of more than 75% of models are shown
29
Global
RCP4.5
RCP8.5
ΔT (K)
1.86
3.73
ΔP (%)
3.70
6.17
Land monsoon domain
ΔT (K)
ΔP (%)
2.06
2.74
4.11
3.61
Present-day: 1986-2005
Future: 2080-2099
Statistics over the monsoon domain are calculated in summer
Global
Land monsoon domain
30
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