HIGH-RESOLUTION CLIMATE - hpc.csiro.au summaries/SOUTH_ENGLISH.pdf · regionally averaged seasonal rainfall changes: timeseries graph of projections by global climate models (gcm)

HIGH-RESOLUTION

CLIMATE PROJECTIONS FOR VIETNAM

REGIONAL SUMMARY | SOUTH

CURRENT TRENDS PROJECTED TRENDS THROUGHOUT THE 21ST CENTURY

Annual temperature observations showed a significant trend of about 0.10 to 0.28°C increase per decade, while annual rainfall observations showed no significant change.

Annual temperature is projected to increase by about 1.4 to 4.4°C by end-of-century.

Little change in annual rainfall amounts is projected, although seasonal changes are apparent.

Heatwaves are projected to be more frequent and longer. The number of hot days is projected to increase.

Droughts are projected to be longer in the southern parts of this region.

Extreme rainfall intensity is projected to increase in the northern parts and decrease in the southern parts of this region.

The intensity of the southwest monsoon is projected to decrease slightly.

Projections indicate that the number of tropical cyclones may decrease. Other studies have also suggested some increases in intensity.

Sea levels are projected to rise by about 100 to 400mm by mid-century, with further increase by end-of-century and beyond.

KEY FINDINGS

ABOUT THIS PUBLICATION

This Regional Summary has been developed as part of the High-resolution Climate Projections for Vietnam project funded by Australia’s Agency for International Development (AusAID) in order to provide information and data for updating the official climate change and sea-level rise scenarios for Vietnam in 2015. This brochure provides a summary of the key findings from this research for the South region. For a summary of findings for all of Vietnam see the Project Summary Report and for more detailed information on the scientific approach and results see the Technical Report (available in 2014). All publications and climate projection information can be accessed on the project website:

www.vnclimate.vn

SO UTH 1

CLIMATE FEATURES1

• Annual average temperature: 26.5 to 27°C• Maximum temperature: 38 to 40°C• Minimum temperature: 14 to 18°C• Annual average rainfall: 1600 to 2000mm• Daily maximum rainfall: 150 to 350mm• Rainfall season: May to Nov

The station trend analyses (below) are based upon all available data within the last 50 years (1961–2010).

ANNUAL TEMPERATURE HAS INCREASED

Temperature in this region has increased by approximately 0.04 to 0.28°C per decade (Figure 2). It should be noted that only increases of 0.10°C per decade and above are significant2.

MAXIMUM AND MINIMUM TEMPERATURES HAVE BOTH INCREASED

Both maximum and minimum daily temperatures have generally increased in this region. Over the whole region, maximum and minimum temperatures have increased by up to 0.36°C per decade.

SLIGHTLY FEWER HOT DAYS

The number of hot days3 has decreased significantly by 3 days per decade at the Can Tho station. All other stations show no significant trend.

ANNUAL RAINFALL HAS NOT CHANGED

Most station observations have not shown any significant change in rainfall (Figure 3). The only significant changes are at the Vung Tau station (north coast), with a decrease of about 4% per decade.

EXTREME RAINFALL AMOUNTS ARE MOSTLY UNCHANGED

Annual maxima of 1-day and 5-day rainfall amounts appear to remain unchanged in the Mekong Delta. The number of very wet days has increased significantly in this region, meaning that the number of heavy rainfall days has also increased, even though the extreme rainfall amounts have remained mostly unchanged.

1 Nguyễn Đức Ngữ, Nguyễn Trọng Hiệu (2004). Khí hậu và tài nguyên khí hậu, NXB Nông nghiệp. Hà Nội.2 Statistical significance has been calculated using the Mann-Kendall test.

3 Hot days with temperatures above 35°C.

CURRENT CLIMATE

FIGURE 1. MAP OF VIETNAM WITH SOUTH REGION HIGHLIGHTED.

HOANG SA ISLANDS

CON DAO ISLAND

PHU QUOC ISLAND

TRUONG SA ISLANDS

H I G H - R ESO LUT I O N CL I MATE PROJ ECT I O N S FO R V I ETNAM2

FIGURE 2. ANNUAL TEMPERATURE TRENDS BASED ON STATION OBSERVATIONS. TEMPERATURE CHANGES ARE INDICATED FOR EACH STATION IN °C PER DECADE. RED CIRCLES REPRESENT AN INCREASING TREND AND BLUE CIRCLES, DECREASING. CIRCLES ARE FILLED WHERE THERE ARE STATISTICALLY SIGNIFICANT TRENDS2. ELEVATION IS INDICATED BY THE COLOUR BAR TO THE RIGHT AND LIGHT BLUE LINES REPRESENT MAJOR RIVERS.

FIGURE 3. ANNUAL RAINFALL TRENDS BASED ON STATION OBSERVATIONS. RAINFALL CHANGES ARE INDICATED FOR EACH STATION IN PERCENT CHANGE PER DECADE. RED CIRCLES REPRESENT A DECREASING TREND AND BLUE CIRCLES, INCREASING. CIRCLES ARE FILLED WHERE THERE ARE STATISTICALLY SIGNIFICANT TRENDS2. ELEVATION IS INDICATED BY THE COLOUR BAR TO THE RIGHT AND LIGHT BLUE LINES REPRESENT MAJOR RIVERS.

0.24CAMAU

0.16CANTHO

0.04RACHGIA 0.28

VUNGTAU

0.19CONDAO

0.17

PHUQUOC

104E 105E 106E 107E 108E 109E

8N

9N

10N

11N

12N

0

500

1000

1500

2000

2500

3000m

104E 105E 106E 107E 108E 109E

8N

9N

10N

11N

12N

CAMAU

CANTHORACHGIA

VUNGTAU

CONDAO

PHUQUOC

104E 105E 106E 107E 108E 109E

8N

9N

10N

11N

12N

0

500

1000

1500

2000

2500

3000m

0.270.26−4.85

−0.74

−3.83

−0.21

SO UTH 3

FUTURE CLIMATE

Regional and global models4 are used to project changes in rainfall and temperature by mid-century (2045–2065) and end-of-century (2080–2099) relative to the baseline period (1980–2000).

TEMPERATURE INCREASES

Projections from regional models for average temperature changes by mid-century and end-of-century are presented in Table 1. The warming is very clear, with an increase in annual temperature of about 1.4 to 2.5°C by mid-century and 2.6 to 4.4°C by end-of-century for the higher (RCP8.5) greenhouse gas scenario. Less warming is evident in the lower (RCP4.5) greenhouse gas scenario.

TABLE 1. SUMMARY OF TEMPERATURE CHANGES (IN °C) ANNUALLY AND BY SEASON5 FROM REGIONAL MODELS FOR THE LOWER (RCP4.5) AND HIGHER (RCP8.5) GREENHOUSE GAS SCENARIOS BY MID-CENTURY (2045–2065) AND END-OF-CENTURY (2080–2099). THE AMOUNT OF CHANGE AND THE LEVEL OF AGREEMENT AMONGST MODELS ARE INDICATED BY SHADING.

ANNUAL CHANGES

SEASONAL CHANGES

NEMS DEC–MAR

FIMS APR–MAY

SWMS JUN–SEP

SIMS OCT–NOV

2045–2065

LOWER GREENHOUSE GAS SCENARIO (RCP4.5)

+1.1 to +2.0 +1.1 to +2.0 +0.9 to +1.9 +1.0 to +2.1 +1.1 to +2.0

HIGHER GREENHOUSE GAS SCENARIO (RCP8.5)

+1.4 to +2.5 +1.4 to +2.5 +1.3 to +2.5 +1.3 to +2.6 +1.4 to +2.6

2080–2099


+1.4 to +2.6 +1.5 to +2.6 +1.3 to +2.6 +1.4 to +2.6 +1.2 to +2.5


+2.6 to +4.4 +2.5 to +4.4 +2.8 to +4.3 +2.5 to +4.5 +2.6 to +4.3

Small increase—Half or more projections show increases of less than 2°C

Medium increase—More than half of projections show increases of 2 to 4°C

High increase—Half or more projections show increases of greater than 4°C

4 These are global climate models from the Coupled Model Intercomparison Project Phase 5 that will be used in the Intergovernmental Panel on Climate Change’s Fifth Assessment Report.

5 Given the influence of monsoons on Vietnam’s climate, monsoon-based seasons have been used in these analyses: North East Monsoon Season (NEMS), First Inter-Monsoon Season (FIMS), South West Monsoon Season (SWMS) and Second Inter-Monsoon Season (SIMS).


TEMPERATURE INCREASES

Projections of changes over time by global models, and the range of changes by end-of-century for both global and regional models, are presented for temperature in Figure 4. Both global and regional models agree on large increases in temperature by end-of-century, with less warming in the lower (RCP4.5) greenhouse gas scenario. However, projections by the regional models show slightly less warming in all seasons except for the SWMS (Jun–Sep). The varying amounts of temperature increase signify the need to consider both mid-range and extreme changes.

FIGURE 4. REGIONALLY AVERAGED SEASONAL TEMPERATURE CHANGES: TIMESERIES GRAPH OF PROJECTIONS BY GLOBAL CLIMATE MODELS (GCM) SHOWN ON THE LEFT, FOR HIGHER (RCP8.5) GREENHOUSE GAS SCENARIO. END-OF-CENTURY SUMMARY OF PROJECTIONS BY GLOBAL CLIMATE MODELS (GCM) AND REGIONAL CLIMATE MODELS (RCM) SHOWN AS BARS, ON THE RIGHT, FOR BOTH LOWER (RCP4.5) AND HIGHER (RCP8.5) SCENARIOS.

TIME

FIRST INTER-MONSOON SEASON (APR–MAY)

GCM TIMESERIES—RCP 8.5 (HIGHER)

TEM

PER

ATU

RE

(°C)

CHA

NG

E IN

TEM

PER

ATU

RE

(°C)

CO

MPA

RED

TO H

ISTO

RIC

BA

SELI

NE

PER

IOD

(19

80–2

000)

RCP4.5(LOWER)

RCP 8.5(HIGHER)

GCM

GCM

1900 1950 2000 2050 2100

−1

0

1

2

3

4

5

27

28

29

30

31

32

33

RCM

RCM

END OFCENTURYSUMMARY

TIME

SOUTH WEST MONSOON SEASON (JUN–SEP)


TEM

PER

ATU

RE

(°C)

CHA

NG

E IN

TEM

PER

ATU

RE

(°C)

CO

MPA

RED

TO H

ISTO

RIC

BA

SELI

NE

PER

IOD

(19

80–2

000)

RCP4.5(LOWER)

GCM

1900 1950 2000 2050 2100

−1

0

1

2

3

4

5

26

27

28

29

30

31

32

RCM

RCM

GCM

RCP 8.5(HIGHER)


SO UTH 5

25

26

27

28

29

30

31

TIME

SECOND INTER-MONSOON SEASON (OCT–NOV)


TEM

PER

ATU

RE

(°C)

CHA

NG

E IN

TEM

PER

ATU

RE

(°C)

CO

MPA

RED

TO H

ISTO

RIC

BA

SELI

NE

PER

IOD

(19

80–2

000)

RCP4.5(LOWER)

GCM

1900 1950 2000 2050 2100

−1

0

1

2

3

4

5

RCM

RCM

GCM

RCP 8.5(HIGHER)


24

25

26

27

28

29

30

TIME

NORTH EAST MONSOON SEASON (DEC–MAR)


TEM

PER

ATU

RE

(°C)

CHA

NG

E IN

TEM

PER

ATU

RE

(°C)

CO

MPA

RED

TO H

ISTO

RIC

BA

SELI

NE

PER

IOD

(19

80–2

000)

RCP4.5(LOWER)

GCM

1900 1950 2000 2050 2100

−1

0

1

2

3

4

5

RCM

RCM

GCM

RCP 8.5(HIGHER)


LEGEND:

1. Middle (bold) line is the mid-point value (median) of GCM or RCM simulations from multiple models over a 20-year average.

2. Shaded area is between the upper and lowerranges (90th and 10th percentiles) of GCMor RCM simulations from multiple modelsover a 20-year average.

This represents the potential range of projections in any given 20-year period.


SOME SEASONAL CHANGES IN RAINFALL

Similar to temperature, projections of seasonal rainfall changes over time by global models, and the range of changes by end-of-century for both global and regional models, are presented in Figure 5. These projections for rainfall show larger variations in the direction of change than were projected for temperature. This reinforces the need to consider both mid-range and extreme changes.

FIGURE 5. REGIONALLY AVERAGED SEASONAL RAINFALL CHANGES: TIMESERIES GRAPH OF PROJECTIONS BY GLOBAL CLIMATE MODELS (GCM) SHOWN ON THE LEFT, FOR HIGHER (RCP8.5) GREENHOUSE GAS SCENARIO. END-OF-CENTURY SUMMARY OF PROJECTIONS BY GLOBAL CLIMATE MODELS (GCM) AND REGIONAL CLIMATE MODELS (RCM) SHOWN AS BARS, ON THE RIGHT, FOR BOTH LOWER (RCP4.5) AND HIGHER (RCP8.5) SCENARIOS.

TIME

FIRST INTER-MONSOON SEASON (APR–MAY)

RCP4.5(LOWER)

RCM

1900 1950 2000 2050 2100


RA

INFA

LL (

MM

/MO

NTH

)

% C

HA

NG

E IN

RA

INFA

LL C

OM

PAR

ED T

OH

ISTO

RIC

BA

SELI

NE

PER

IOD

(19

80–2

000)

GCM

RCP 8.5(HIGHER)50

100

150

200

−50

0

50GCM

RCM


TIME

SOUTH WEST MONSOON SEASON (JUN–SEP)

RCP4.5(LOWER)

1900 1950 2000 2050 2100


RA

INFA

LL (

MM

/MO

NTH

)

% C

HA

NG

E IN

RA

INFA

LL C

OM

PAR

ED T

OH

ISTO

RIC

BA

SELI

NE

PER

IOD

(19

80–2

000)

GCM

RCP 8.5(HIGHER)

−50

0

50

150

200

250

300

350

400

450

GCM

RCMRCM


SO UTH 7

200

300

400

500

TIME

SECOND INTER-MONSOON SEASON (OCT–NOV)

RCP4.5(LOWER)

1900 1950 2000 2050 2100


RA

INFA

LL (

MM

/MO

NTH

)

% C

HA

NG

E IN

RA

INFA

LL C

OM

PAR

ED T

OH

ISTO

RIC

BA

SELI

NE

PER

IOD

(19

80–2

000)

GCM

RCP 8.5(HIGHER)

−50

0

50GCM

RCM

RCM


20

30

40

50

60

70

TIME

NORTH EAST MONSOON SEASON (DEC–MAR)

RCP4.5(LOWER)

1900 1950 2000 2050 2100


RA

INFA

LL (

MM

/MO

NTH

)

% C

HA

NG

E IN

RA

INFA

LL C

OM

PAR

ED T

OH

ISTO

RIC

BA

SELI

NE

PER

IOD

(19

80–2

000)

GCM

RCP 8.5(HIGHER) −50

0

50

GCM

RCM

RCM


LEGEND:

1. Middle (bold) line is the mid-point value (median) of GCM or RCM simulations from multiple models over a 20-year average.

2. Shaded area is between the upper and lowerranges (90th and 10th percentiles) of GCMor RCM simulations from multiple modelsover a 20-year average.

This represents the potential range of projections in any given 20-year period.


SOME SEASONAL CHANGES IN RAINFALL

Projections from regional models for annual rainfall (Table 2) show large variations in both direction and amount of change. However, there is medium agreement on increases projected for the NEMS (Dec–Mar), with even greater agreement on increases for the FIMS (Apr–May) by mid-century.

TABLE 2. SUMMARY OF RAINFALL CHANGES (IN %) ANNUALLY AND BY SEASON5 FROM REGIONAL MODELS FOR THE LOWER (RCP4.5) AND HIGHER (RCP8.5) GREENHOUSE GAS SCENARIOS BY MID-CENTURY (2045–2065) AND END-OF-CENTURY (2080-2099). THE LEVEL OF AGREEMENT IN CHANGE AMONGST MODELS IS INDICATED BY SHADING.

ANNUAL CHANGES

SEASONAL CHANGES

NEMS DEC–MAR

FIMS APR–MAY

SWMS JUN–SEP

SIMS OCT–NOV

2045–2065


-4 to +27 -5 to +24 +2 to +18 -18 to +37 -14 to +30


-10 to +36 -5 to +22 0 to +27 -16 to +61 -14 to +28

2080–2099


-8 to +26 -16 to +7 -5 to +7 -17 to +48 -6 to +37


-18 to +52 -31 to +57 -11 to +51 -21 to +93 -18 to +72

High agreement on decrease—All projections show decrease

Medium agreement on decrease—More than half of the projections show decrease less than -10%

Low agreement on change—Projections do not agree or show little change

Medium agreement on increase—More than half of the projections show increase greater than +10%

High agreement on increase—All projections show increase

CLIMATE EXTREMES

Projected changes throughout the 21st century for a number of key climate extremes that affect this region are summarised below:

MORE AND LONGER HEATWAVES

The number and length of heatwaves (consecutive periods with hot conditions) are projected to increase significantly by end-of-century.

INCREASE IN NUMBER OF HOT DAYS

The number of hot days (days with maximum temperatures above 35°C) is projected to increase throughout the 21st century. The amount of increase varies between the different regional models.

MORE INTENSE EXTREME RAINFALL IN NORTHERN PARTS, LESS INTENSE IN SOUTHERN PARTS

Due to their rarity, changes in extreme rainfall events (annual maxima of 1-day and 5-day rainfall amounts) are not easy to project and are often associated with a large degree of uncertainty. Nevertheless, some projections by regional models show a tendency towards more intense extreme rainfall in the northern parts and less intense in the southern parts.

LONGER DROUGHTS IN SOME AREAS

Some projections by regional models show that droughts may last longer in the southern parts of this region, especially by end-of-century.

SOUTHWEST MONSOON WEAKENS SLIGHTLY

Based on some projections by regional models, the intensity of the southwest monsoon is expected to decrease slightly by end-of-century.

FEWER BUT POSSIBLY MORE INTENSE TROPICAL CYCLONES (TYPHOONS)

Preliminary analysis of projections by regional models in this study suggests that the number of tropical cyclones may decrease in the East Vietnam Sea by mid-century. Other studies support this decreasing trend and suggest increases in intensity by end-of-century.

SEA LEVELS WILL CONTINUE TO RISE

The new projections indicate that the rate of sea-level rise during this century will be larger than the last. Sea levels rise approximately 100 to 400mm by mid-century with further increase by end-of-century and beyond. In addition, ground subsidence can occur in regions where there is ground water extraction or possible loss of sediment supply as rivers become more managed (i.e. more dams). These effects may be contributing to the substantially larger rates of relative sea-level rise at some locations.

CONTACT

VIETNAM INSTITUTE OF METEOROLOGY, HYDROLOGY AND ENVIRONMENTWEB http://www.imh.ac.vn/ Assoc. Prof. Dr. Nguyen Van ThangEMAIL [email protected] +84 - 4 - 38359415 For more information, please visit the project website: WWW.VNCLIMATE.VN

Documents

HIGH-RESOLUTION CLIMATE - hpc.csiro.au summaries/SOUTH_ENGLISH.pdf · regionally averaged seasonal rainfall changes: timeseries graph of projections by global climate models (gcm)