Download Projection of Climatic Change over Japan Due to Global Warming

SOLA, 2005, Vol. 1, 097 100, doi: 10.2151/sola. 2005 026
97
Projection of Climatic Change over Japan Due to Global Warming
by High-Resolution Regional Climate Model in MRI
Kazuo Kurihara1, Koji Ishihara2, Hidetaka Sasaki1, Yukio Fukuyama2, Hitomi Saitou2,
Izuru Takayabu1, Kazuyo Murazaki1, Yasuo Sato1, Seiji Yukimoto1 and Akira Noda1
1
Meteorological Research Institute, Tsukuba, Japan
2
Japan Meteorological Agency, Tokyo, Japan
The Meteorological Research Institute (MRI) and the
Japan Meteorological Agency (JMA) projected climate
change over Japan due to global warming using a highresolution Regional Climate Model of 20 km mesh size
(RCM20) developed in MRI. Projection was made for
2081 to 2100 following a SRES-A2 scenario.
Precipitation projected by RCM20 indicated that increased daily precipitation will be seen during the warm
season from June to September. Except for this period,
the precipitation amount will not change much or will
slightly decrease around Japan. The increase during the
warm season will be seen only in the western part of
Japan. A possible cause of the increase is an El Ni
no-like
SST pattern in the future. Due to the future increased
summer SST in the eastern equatorial Pacific, anticyclonic circulation to the south of Japan will intensify
and will induce a strong water vapor flux along the rim
of the anti-cyclonic anomaly. The intensified flux will
converge over the western part of Japan and may
increase precipitation.
Surface air temperature is projected to increase more
than 2°C around Japan in January. In summer, the temperature increase will be lower by about 1°C than in
winter.
1. Introduction
Climate change over Japan due to global warming is
inducing serious concerns among the Japanese public,
political, and industrial sectors. To prevent disaster and
maintain the quality of the environment, we need information and data to understand possible climate change
that is induced by increasing artificial emission of
carbon dioxide and other greenhouse gases. Many
studies have been made with General Circulation
Models (GCMs) for projections of climate change (IPCC
2001). However, mesh sizes of GCMs are too large for
analyzing regional climate change. The Meteorological
Research Institute (MRI) and the Japan Meteorological
Agency (JMA) therefore developed a high-resolution
Regional Climate Model of 20 km mesh size (RCM20)
that could be used for regional climate projection over
Japan due to global warming. The climate change over
Japan had already been investigated with a former
version of a 40 km-mesh regional climate model developed in MRI and reported by JMA (JMA 2001; Ichikawa
2004). The National Institute for Environmental Studies
(NIES) and the Central Research Institute of Electric
Power Industry (CRIEPI) also projected climate change
over Japan (Ichikawa 2004). Those reports included projections only for January or winter and climate change
in each area of Japan had not yet been adequately determined for all seasons. Using RCM20, we projected
climate change throughout the whole year. Furthermore, regional climate change was also investigated
Corresponding author: Kazuo Kurihara, Meteorological
Research Institute, 1-1 Nagamine, Tsukuba 305-0052, Japan.
E-mail: [email protected]. ©2005, the Meteorological
Society of Japan.
with the model. This paper reports the structure and
performance of the developed RCM20 first. The projected climate change over Japan in the late 21st
century due to global warming is then presented, based
on the results calculated by RCM20.
2. Description of RCM20
RCM20 was developed at MRI for studying the
regional climate around Japan, based on the Regional
Spectral Model (RSM) (NPD/JMA 1997), which has been
used at JMA for operational weather forecasting. The
horizontal grid interval of RCM20 is 20km at 30°N and
60°N on a Lambert projection map. It has a 129 × 129
grid, and the domain covers 2500 km × 2500 km around
Japan. It has 36 vertical layers. Arakawa-Schubert and
moist convective adjustment schemes were used for
convection parameterization. The level 2 scheme of
Mellor and Yamada (1974) was adopted for the boundary-layer process. For long-term integration, a landsurface process developed by Takayabu (2003) and the
Spectral Boundary Coupling (SBC) method developed at
MRI (Kida et al. 1991; Sasaki et al. 1995; Sasaki et al.
2000) were incorporated into RCM20 for a nesting
scheme.
Long-term integrations by RCM20 were conducted
for the present climate (1981 to 2000) and the future
climate (2081 to 2100). The double-nesting technique
was utilized for the integrations. For an outermost
model, the Coupled General Circulation Model (MRICGCM2) (Yukimoto et al. 2001), with a horizontal resolution of T42 (280km) and 30 vertical layers, was used.
The MRI-CGCM2 provided the boundary condition to a
60km-mesh regional climate model (RCM60), and
RCM60 provided the boundary condition to RCM20.
RCM60 has the same configuration as RCM20, except
for the mesh size and the grid number (173 × 129 for
RCM60). Sea-surface temperatures (SST) for RCM20 and
RCM60 were supplied from MRI-CGCM2 and interpolated to the RCMs’ model grids. Over each grid point,
SST was adjusted so that the 20-year average of daily
SST was equal to the 20-year average of the observed
SST for each day, which was obtained from NOAA/
AVHRR (National Oceanic and Atmospheric Administration/Advanced Very High Resolution Radiometer)
data and also interpolated to RCMs’ grid point in the
present-climate run. Due to this, fluctuation of the SST
which included in the original SST by MRI-CGCM2
remains in RCM simulations.
For the future-climate run, the SRES-A2 scenario
(IPCC 2000) was adopted for atmospheric concentration
of carbon dioxide. SST in the future run was calculated
from SST projected by MRI-CGCM2 and adjusted with
the same value (difference between the 20-year averages
of CGCM2-SST and observed-SST for each day) that
was used in the present-climate run over each grid
point.
3. Reproducibility of present climate
Using the result of the present-climate experiment,
98
Kurihara et al., Regional Climate Projection
Fig. 1. Observation stations that were used to evaluate
accuracy of RCM20 results. Colors indicate areas of Japan.
Dark blue: North Japan/Japan Sea side (NJ). Light blue: North
Japan/Pacific side (NP). Dark green: East Japan/Japan Sea side
(EJ). Light green: East Japan/Pacific side (EP). Orange: West
Japan/Japan Sea side (WJ). Yellow: West Japan/Pacific side
(WP). Red: South-West Islands (SWI).
performance was evaluated in seven local areas of Japan
(Fig. 1). Precipitation amount was reproduced adequately in each area, compared with the climatic
amount of observed precipitation that was calculated
from data by observation stations of JMA (e.g., Fig. 2). In
Fig. 2, monthly mean precipitation amounts from the
result of RCM20 and from observations are indicated
for areas of NJ (North Japan/Japan Sea side) and WJ
(West Japan/Japan Sea side). The observed climatic precipitation amount was calculated by averaging data at
observation stations included in each area. To calculate
the model climate, model grid data nearest each observation station was chosen. The chosen data were
gathered and averaged in each area to obtain the areal
model climate. In the figure, differences between model
climates and observations were seen. However, Fig. 2
shows that total differences were not too large. Model
results agreed to observations mostly with a significance level of 95%. In other areas, climatic precipitation
amounts were reproduced with similar accuracy as Fig.
2 for most cases. We can conclude that the model could
reproduce the annual change of precipitation for each
area of Japan with adequate accuracy. The exception
was the area of SWI, where observation stations are few
and reproducibility was not adequate. In this paper,
results of SWI are not discussed.
Surface air temperatures are plotted in scatter
diagrams in Fig. 3. One dot represents data at each observation station. From the figure, high correlations
between model results and observations can be seen for
January and July. The temperatures had warm biases of
2°C in all areas for summer and winter. For reduction of
this bias, we may need further sophistication of surface
process of RCMs in the future. However, high correlation coefficients exceeding 0.95 were attained between
model results and observations for all months. The coefficient was 0.95 for January and 0.97 for July, as presented in Fig. 3.
These results indicated that RCM20 was able to
reproduce present climate over Japan with adequate
accuracy.
4. Future climate projected by RCM20
4.1 Precipitation
Daily precipitation amounts around Japan calculated
by RCM20 are plotted in Fig. 4 for the present climate
(1981 to 2000) and future climate (2081 to 2100). One
noticeable future climate change around Japan is that
Fig. 2. Monthly precipitation amounts in areas of NJ (upper
panel) and WJ (lower panel). Unit of ordinate is mm/month.
Blue bars indicate observed monthly precipitation amount, and
orange bars indicate RCM20 results.
Fig. 3. Scatter diagrams of mean temperature for January
(upper panel) and July (lower panel). Ordinate indicates model
results and abscissa indicates observation. Units of both axes
are °C. Data of all observation stations in Japan are plotted.
the precipitation amount increases only from June to
September (the summer season). Except that period, the
precipitation amount in the future remains almost the
same or decreases slightly, compared with that in the
present.
This increase of future precipitation in the summer
has geographical characteristics. The increase can be
seen in the western half of Japan (WJ, WP, EJ), but not
in the eastern half (NJ, NP, EP). Figure 5 depicts the rate
of future and present precipitation amounts in the areas
of NJ and WJ. In NJ, the rate of precipitation amount is
nearly 100% throughout the year, indicating that the
future precipitation amount does not change much in
NJ for all seasons. In contrast, in area WJ, the rate increases during the summer season. The same tendency
of increase of precipitation amount can also be seen in
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Fig. 4. Annual change of daily precipitation amount (unit:
mm/day) averaged in the colored area of the left panel, where
change of precipitation is distinct. Red dot: future (2081 to
2100) precipitation amount, black dot: present (1981 to 2000)
precipitation amount. Both are calculated by RCM20. Highfrequency fluctuation is filtered out by adopting a 11-day
running mean.
areas of WP and EJ. Further, in the western part of
Japan, year-to-year fluctuation of precipitation amount
is projected to increase in the summer (figures not
shown).
One possible reason for this increase of summer precipitation is the change of circulation around Japan in
the future (Fig. 6). MRI-CGCM2 projects that SST will
increase in the eastern equatorial Pacific during the
summer in the future. The change of SST around the
equatorial Pacific region will resemble that of an El
Ni
no event. During such an event, the subtropical high
pressure to the south of Japan intensifies (Ishihara et al.
2004). The same intensification of the high pressure is
seen in the result of MRI-CGCM2. Figure 6, plotted
using the result of MRI-CGCM2, depicts a positive
500hPa height anomaly, which indicates intensification
of the high pressure, seen along 20°N (from 80°E to
160°W). Around the center of the positive height
anomaly, precipitation is projected to decrease (warmcolored area) in the future. However, along the rim of
the high-pressure anomaly, precipitation is projected to
increase (cool-colored area) due to the intensified horizontal flux of water vapor. The western part of Japan is
located just in the area of intensified water vapor flux
from the southwest direction and increased precipitation amount.
The El Ni
no-like pattern of SST in the equatorial
Pacific Ocean can be seen in results projected by many
CGCMs (IPCC 2001). The El Ni
no-like SST pattern
changes circulation around Japan, as indicated by a
previous study (Ishihara et al. 2004). This is considered
to support the reliability of the projection by RCM20
that precipitation will increase in the western part of
Japan during the summer season.
4.2 Surface air temperature
Surface air temperature is projected to increase more
than 2°C around Japan in January (Fig. 7). The temperature increase will be large at high latitudes, and the
maximum of increase will exceed 4°C around the
Okhotsk Sea. The temperature increase will be lower in
summer than in winter. In July, the increase around
Japan will exceed 1.5°C, with a maximum of more than
3°C around the Okhotsk Sea (figures not shown).
Figure 8 depicts the monthly temperature increases
for NJ and WJ. Distinct annual changes will be seen for
both areas. The temperature increase in the summer will
be lower than that in the winter, with a difference of 1
°C. This tendency also can be seen in the results of MRICGCM2 (Yukimoto et al. 2001) and may be due to future
change of snow or ice cover.
Fig. 5. Rate of future and present precipitation amount (unit: %).
More than 100% indicates increase in the future. Upper is for NJ
area, lower for WJ area.
Fig. 6. Change of summer circulation around Japan in the
future projected by MRI-CGCM2. Differences between the
future run (2081 to 2100) and the present run (1981 to 2000)
are plotted. Isolines, drawn every 5 m, indicate change of
500hPa height (unit: m). The global mean of the height
anomaly is removed from the height change. Change of daily
precipitation amount is indicated by colors (unit: mm/day).
Warm colors indicate areas of decreasing precipitation amount,
and cool colors indicate increasing areas as shown by the color
bars. Arrows represent change of 850hPa wind.
The absolute value of the temperature increase is
controlled by MRI-CGCM2, which provides a boundary
condition to RCM20. The global temperature increase
for the A2 scenario projected by MRI-CGCM2 is 2.5°C in
2100 (JMA 2003), while that reported by IPCC is
between 2.5°C and 5°C (IPCC 2001). The absolute value
of temperature increase has some uncertainty and will
possibly be larger than the result shown in this study by
RCM20.
5. Summary
MRI developed a high-resolution Regional Climate
Model of 20 km mesh size (RCM20) for projecting
climate change over Japan due to global warming.
Utilizing the SBC scheme developed in MRI (Kida et al.
1991; Sasaki et al. 2001; and Sasaki et al. 2005), RCM20
is nested in MRI-CGCM2 (Yukimoto et al. 2001). Using
100
Kurihara et al., Regional Climate Projection
Fig. 7. Temperature increase in the future (2081 to 2100). Unit
is °C. Difference between the present and future climates is
plotted for January.
tion around Japan will change so that high-pressure circulation to the south of Japan will intensify. This intensification of the anti-cyclonic circulation will induce a
strong water vapor flux anomaly along the rim of the
anti-cyclonic anomaly. The water vapor flux will converge over the western part of Japan from the southwest and may bring about increased precipitation
around western Japan.
Surface air temperature is projected to increase more
than 2°C around Japan in January. The temperature
increase will be large at high latitudes, and the
maximum increase will exceed 4°C around the Okhotsk
Sea. A distinct annual change will be seen in the temperature increase in the future. The temperature
increase in summer will be lower than in winter. The
difference of increase will be 1°C between summer and
winter.
Although projection of future climate change due to
global warming over Japan was an important issue for
many Japanese sectors, we had very few information to
understand the future climate change until results by
RCM20 became available. RCM20 enabled to project the
climate change to its details for the first time. Further,
we have presented a global background for the climate
change around Japan. Projections described in this
paper will give a basis for investigating the climate
change due to global warming. However, RCM20 is not
perfect enough as indicated in section 3. Further efforts
are needed to sophisticate the model for reproducing realistic present climate and accurate projection of future
climate.
Fig. 8. Monthly temperature increase for areas NJ and WJ. Unit
is °C. Difference between the present and future climates is
plotted.
this model, MRI and JMA conducted a present-climate
experiment for 1981 to 2000 and a future-climate experiment for 2081 to 2100. The SRES-A2 scenario,
proposed by IPCC (IPCC 2000), was adopted for the
future run.
Reproducibility of the present climate by RCM20
was evaluated with observation data over Japan. The
present-climate run by RCM20 exhibited sufficient
accuracy in reproducing the present climate. The precipitation amount in regions of Japan was reproduced
adequately, though there were some exceptional cases.
Surface air temperature was reproduced with a high
correlation coefficient exceeding 0.95 between model
results and observed temperature.
The precipitation projected by RCM20 for the late
21st century possessed distinct characteristics. Specifically, the increase of daily precipitation amount will be
seen only during the warm season from June to September. Except for during this period, the precipitation
amount will not change much or will decrease slightly
around Japan. The increase during the warm season will
be seen in only the western part of Japan. A possible
cause of the increase during the warm season is an El
Ni
no-like future SST pattern, projected by MRI-CGCM2.
Based on the summer increase of future SST in the
eastern equatorial Pacific, future atmospheric circula-
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Manuscript received 28 April 2005, accepted 24 June 2005
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