Webinar Series on Climate Change Projection for Disaster Risk Reduction in Asia-Pacific Region, 10 January 2024

How are future climates projected under aglobal warming in a computer?
～Advantages of a high resolution model～
Tosiyuki NAKAEGAWA
Japan Meteorological Business Support Center
Meteorological Research Institute, Tsukuba, Japanadvanced studiesof climate changeprojection

How is a future climate projected?
IPCC AR6 WGI Interactive Atlas

IPCC AR6 WGI Report

Today’s contents••

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Basics of future climate projections in a computer
Advantages of a model with a higher horizontal resolution
Webinar January 10, 2024Processes in the Earth System

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(FAQ1.2 Fig. 1: IPCC AR4 WGI 2007)

Development of CGCMs(Fig.1.13; IPCC 2013a).

Configuration of a GCM for future climate projections
Atmosphere, land, andocean are discretized:
Atmospher:320x160x48
Ocean:
360x364x51

Flows and physicalprocesses are simulated
for each gridMeteorologicalResearchInstitute•(Yukimoto et al. 2011)
Webinar January 10, 2024

(Courtesy of Yukimoto@MRI)

How these processes are implemented in a computer?
Navier-Stokes equation

A code for a computer

Discretization of the equations above

do j=1,latg2_
do i=1,lonf2_
ftsea(i,j)=ftsea(i,j)+tsea(i,j)*weight(ifstep)
fsheleg(i,j)=fsheleg(i,j)+sheleg(i,j)*weight(ifstep
ftg3(i,j)=ftg3(i,j)+tg3(i,j)*weight(ifstep)
fzorl(i,j)=fzorl(i,j)+zorl(i,j)*weight(ifstep)
fplantr(i,j)=fplantr(i,j)+plantr(i,j)*weight(ifstep)
fcv(i,j)=fcv(i,j)+cv(i,j)*weight(ifstep)
do il = 1, 4MeteorologicalResearchInstitutefalbedo(i,j,il)=falbedo(i,j,il)+albedo(i,j,il)*weight(ifstep
enddo
ff10m(i,j)=ff10m(i,j)+f10m(i,j)*weight(ifstep)fcanopy(i,j)=fcanopy(i,j)+canopy(i,j)*weight(ifst
isl=nint(slmsk(i,j))+1
islmsk(i,j,isl)=islmsk(i,j,isl)+1
if(cvb(i,j).ne.cvb0) then
fcvb(i,j)=fcvb(i,j)+cvb(i,j)*weight(ifstep)
wcvb(i,j)=wcvb(i,j)+weight(ifstep)
Webinar January 10, 2024

Emission scenario SSP

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IPCC (2021) Cross Chapter Box 1.4, Figure 1.

Webinar January 10, 2024Historical and future global mean CO2November 6-18, 2022 in Sharm el-Sheikh, Egypt

The shared socio-economic pathway (SSP)of the CMIP6 and actual observed values(GCB 2022)
At the current rate of emissions,the target value of 1.5ºC will bereached in about 10 years.
Photo:Johann Olivier

Given the current emissions rate and global
efforts to reduce emissions, it is not very
likely that SSP2-4.5 will be exceeded.
COP27 reported an increase of 2.5ºC by theend of the century. COP27 reported anincrease of 2.5ºC at the end of the century.

Supercomputer is essential for climate projections
Multi-architecture supercomputer based on
AMD EPYC CPUs, combined withaccelerators, Earth Simulator 4• Cores: total 136,960 processor cores ofAMD EPYC 7742 (Zen2)• GPUs: 64 of Nvidia A100
• Memory: total 556.5 TB
Rank #56(#29• Performance: 19.5 PFLOPS• Interconnection: 200 Gb/s
• Release: 2021
Operational in Deutscher
Wetterdienst since 2019 as wellCPUs

GPUs

Vector engine

https://www.r-ccs.riken.jp/en/fugaku/Needs for high-resolution models
In order to make a progress in
adaptation planning, we need
1. to project future weather extremes
such as typhoon and heavy rainfall
triggering natural disasters, and
2. to assess their impact on our lives.

・ representation of topography depends on resolution
・ low resolution models often fail to reproduce precipitation systems suchas tropical cyclones, stationary front systems, and blocking

・ high resolution models generally have better mean climate
MeteorologicalResearchInstituteWebinar January 10, 2024

Topography dependent on resolutions
Dr. Kusunoki

20km
Real60km
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120km

180km
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Cross section at 87E
Near Everest
Chomolungma or
Qomolangma or

RealMeteorologicalResearchInstituteWebinar January 10, 2024

Dr. Kusunoki

Time-Slice Experiments with high-horizontal resolution
CMIP3 AOGCMs

20km,60km AGCM

5km,2km,1km RCM
Boundarycondition

Atmosphere
SST

Ocean

Projected
Atmosphere
SST
Lower
B.C.

AGCM/RCM is a climate modelversion of the JMA operational
NWP models

SSTESMs
CGCMs
CMIP6
SRESRCP
A1B
Experiments
experiments(2000-2100)

linear trend
in CGCMs

SST for• Present-day climate experiment (1979-2003) observed
AMIP (1979-2003)(2000-2100)
ΔT– the observed sea surface
CGCMs C20C
experiments
temperature (SST) and sea(-2000)
19792003
20752099
ice concentration
present-day climate
future climate• Future climate experiment (2075-2099)
linear trend in CGCMs detrended observed
future change– the warming in the SST for(2075-2099)
SST (1979-2003)
in CGCMs
the CMIP5/6 multi-model
ΔT＋＋＝([2075-2099]ensemble mean is added[1979-2003])
to the observed SST
Mizuta et al. (2008)
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Comparison of reproducibility between
horizontal resolutions

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Precipitation dependent on resolutions
Dr. Kusunoki

Rain
July

250km

100km

Observation
25km

25km

Model
MeteorologicalResearchInstitute

20km

60km
Webinar January 10, 2024

180km

Typhoon prediction between 60km and 20km mesh models

MeteorologicalResearchInstituteWeak central pressure and weak max. windspeed in the 60km mesh model. Reproducibility inthe 20km mesh model is better.

６０km mesh model
２０km mesh model
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Tropical cyclones in the 20-km AGCM

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Future climate projections

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July Precipitation in a future climate
Present-day
1979-2003
Change=(F-P)/P (%)
Increase

Future2075-2099
Decrease
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Maximum 5 day precipitation in a future climate
Increase

Annual statistics

Heavy rainfall

60km

20km
Decrease

Average of 16 experiments
MeteorologicalResearchInstituteOne experiment
Webinar January 10, 2024

SENTAN Theme-3: future climate projections in Japan
CMIP6 AOGCMs

Time-sequential experiments
AOGCM
Atmosphere• (1950-2100)

20km,60km AOGCM

Projected
Ocean
Conditions AtmosphereSST

SST

Ocean

Nudging toobservations

Ocean

Boundarycondition

5km,2km,1km RCM

AGCM/RCM is a climate
model version of the JMA
operational NWP models

linear trend
in CGCMs
CGCMs
SRES A1B
experiments(2000-2100)

observed SST for
AMIP (1979-2003)

Time-sliced experiments
AGCM• Present-day climate(1979-2003)• Future climate(2075-2099)

CGCMs C20Cexperiments(-2000)19792003

present-day climate
future change
in CGCMs

ΔT＋

linear trend in CGCMs(2075-2099)

＋ΔT

2075

detrended observed
SST (1979-2003)＝([2075-2099][1979-2003])

Mizuta et al. (2008)

DDS under the CMIP6 conditions can be performed now!

2099

future climate

Thank you for your attention

MeteorologicalResearchInstituteWebinar January 10, 2024