high-resolution climate - hpc.csiro.au summaries... · regionally averaged seasonal rainfall...

HIGH-RESOLUTION

CLIMATE PROJECTIONS FOR VIETNAM

REGIONAL SUMMARY | NORTH WEST

CURRENT TRENDS PROJECTED TRENDS THROUGHOUT THE 21ST CENTURY

Annual temperature observations showed a significant trend of about 0.09 to 0.26°C increase per decade, while annual rainfall observations showed no significant change.

Annual temperature is projected to increase by about 1.5 to 5.9°C by end-of-century.

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

A small increase is projected in the number and duration of heatwaves. The number of hot days in lower lying areas is projected to increase.

Extreme rainfall tends to decrease by end-of-century.

An increase in long-term droughts is projected.

Southwest monsoon intensity is projected to decrease by end-of-century, with little change in length.

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

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 North West 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

N O RTH WEST 1

CLIMATE FEATURES1

• Annual average temperature: 18 to 22°C• Maximum temperature: 38 to 40°C• Minimum temperature: -2 to 2°C• Annual average rainfall: 1200 to 1600mm• Daily maximum rainfall: 200 to 500mm• Rainfall season: Jun to Aug

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 0.09 to 0.26°C per decade (Figure 2).

MINIMUM TEMPERATURE HAS INCREASED MORE THAN THE MAXIMUM TEMPERATURE

While minimum daily temperature has increased significantly2 by up to approximately 0.31°C per decade, the change in maximum daily temperature is smaller, with increases of approximately 0.19°C per decade.

MORE HOT DAYS AND FEWER COLD NIGHTS

The number of hot days3 has increased by up to 3 days per decade at some stations. The number of cold nights4 has significantly decreased at all stations with the highest rate of up to 5 days per decade.

ANNUAL RAINFALL HAS NOT CHANGED

Station observations have not shown any changes in annual rainfall amounts (Figure 3). There were small decreases evident for stations in the central and southern parts, but most of these changes were not significant. Note that trends for Yen Chau (south), Son La (central), Dien Bien (central) and Lai Chau (north) stations were not significant.

EXTREME RAINFALL AMOUNTS HAVE NOT CHANGED

Annual maxima of 1-day and 5-day rainfall amounts and the number of very wet days remain unchanged for most stations in this region.

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.

4 Cold nights with temperatures below 15°C.

CURRENT CLIMATE

FIGURE 1. MAP OF VIETNAM WITH NORTH WEST 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

500

1000

1500

2000

2500

3000m

LAICHAU

0.09

DIENBIEN

0.26SONLA

0.20YENCHAU

0.24

MOCCHAU

TUANGIAO

0.11

102E 102.5E 103E 103.5E 104E 104.5E 105E102E 102.5E 103E 103.5E 104E 104.5E 105E

20.5N

21N

21.5N

22N

22.5N

23N

20.5N

21N

21.5N

22N

22.5N

23N

0.22

0

500

1000

1500

2000

2500

3000m

102E 102.5E 103E 103.5E 104E 104.5E 105E102E 102.5E 103E 103.5E 104E 104.5E 105E

20.5N

21N

21.5N

22N

22.5N

23N

20.5N

21N

21.5N

22N

22.5N

23N

LAICHAU

0.03

DIENBIEN

0.07SONLA

–2.06YENCHAU

–0.30

MOCCHAU

TUANGIAO

–2.40

–0.85

N O RTH WEST 3

FUTURE CLIMATE

Regional and global models5 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 1.1 to 3.2°C by mid-century and 2.3 to 5.9°C by end-of-century under the high (RCP8.5) greenhouse gas scenario. The largest seasonal increase is projected for the SWMS6 (Jun–Sep) and smallest in the NEMS6 (Dec–Mar). Less warming is evident in the lower (RCP4.5) greenhouse gas scenario.

TABLE 1: SUMMARY OF TEMPERATURE CHANGES (IN °C) ANNUALLY AND BY SEASON6 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)

+0.8 to +2.4 +0.5 to +1.9 +1.0 to +2.0 +1.3 to +2.9 +0.2 to +2.7

HIGHER GREENHOUSE GAS SCENARIO (RCP8.5)

+1.1 to +3.2 +1.0 to +2.7 +0.9 to +2.9 +1.3 to +3.6 +1.2 to +3.6

2080–2099


+1.5 to +3.6 +0.8 to +3.1 +1.3 to +3.6 +2.0 to +4.0 +1.0 to +3.9


+2.3 to +5.9 +2.0 to +4.9 +2.3 to +5.8 +2.4 to +6.8 +2.7 to +6.3

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

5 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.

6 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)

END OFCENTURYSUMMARY

RCM

RCP4.5(LOWER)

RCM

RCP 8.5(HIGHER)

GCM

GCM

1900 1950 2000 2050 2100

0

2

4

6

24

26

28

30

32

TIME


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)


RCM

RCP4.5(LOWER)

RCM

RCP 8.5(HIGHER)

GCM

GCM

1900 1950 2000 2050 2100

0

2

4

6

26

28

30

32

34

SOUTH WEST MONSOON SEASON (JUN–SEP)

N O RTH WEST 5

22

24

26

28

TIME


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)


RCM

RCP4.5(LOWER)

RCM

RCP 8.5(HIGHER)

GCM

GCM

1900 1950 2000 2050 2100

0

2

4

6

SECOND INTER-MONSOON SEASON (OCT–NOV)

18

20

22

24

TIME


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)


RCM

RCP4.5(LOWER)

RCM

RCP 8.5(HIGHER)

GCM

GCM

1900 1950 2000 2050 2100

0

2

4

6

NORTH EAST MONSOON SEASON (DEC–MAR)

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. The only season with nearly consistent changes is the SIMS (Oct–Nov), which mainly shows increases in rainfall by both global and regional models. 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.

1900 1950 2000 2050 2100

−40

−20

0

20

40

60

80

GCM

RCM

GCM

RCM100

150

200

250

TIME

FIRST INTER-MONSOON SEASON (APR–MAY)


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)

RCP4.5(LOWER)

RCP 8.5(HIGHER)


1900 1950 2000 2050 2100

GCM

RCM

GCM

RCM

150

200

250

300

350

400

450

−40

−20

0

20

40

60

80

TIME

SOUTH WEST MONSOON SEASON (JUN–SEP)


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)

RCP4.5(LOWER) RCP 8.5

(HIGHER)


N O RTH WEST 7

1900 1950 2000 2050 2100

GCM

RCM

GCM

RCM

60

80

100

120

140

−40

−20

0

20

40

60

80

TIME

SECOND INTER-MONSOON SEASON (OCT–NOV)


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)

RCP4.5(lower)

RCP 8.5(higher)


20

30

40

50

1900 1950 2000 2050 2100

GCM

RCM

GCM

RCM −40

−20

0

20

40

60

80

TIME

NORTH EAST MONSOON SEASON (DEC–MAR)

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)

RCP4.5(lower)

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

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 projected rainfall increases for the SIMS6 (Oct–Nov) by end-of-century. For the FIMS (Apr–May), there is medium agreement on projected rainfall decreases by end-of-century.

TABLE 2: SUMMARY OF RAINFALL CHANGES (IN %) ANNUALLY AND BY SEASON6 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


-16 to +12 -7 to +27 -17 to +12 -22 to +19 -28 to +57


-10 to +3 -26 to +19 -18 to +16 -15 to +10 -28 to +13

2080–2099


-14 to +7 -22 to +57 -12 to +2 -23 to +14 -32 to +55


-22 to +10 -41 to +23 -31 to -+2 -35 to +16 -10 to +59

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:

SMALL INCREASES IN HEATWAVES

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

INCREASE IN HOT DAYS IN SOME PARTS

The number of hot days (days with maximum temperatures above 35°C) is projected to increase in the lower lying areas of this region. Since temperature decreases with height, increases in hot days are not projected to reach the mountainous areas of this region, even by end-of-century.

LESS INTENSE EXTREME RAINFALL

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 regional projections show a tendency for more intense 1-day extreme rainfall by mid-century, although the change becomes unclear by end-of-century. The intensity of the 5-day extreme rainfall tends to decrease.

LONG-TERM DROUGHTS INCREASE

Some projections by regional models show that short-term droughts (3-month consecutive periods with a rainfall deficit) will decrease in frequency, while long-term droughts (12-month) will increase in frequency and duration.

SOUTHWEST MONSOON REMAINS UNCHANGED

Based upon some projections by regional models, the length and intensity of the southwest monsoon are expected to remain unchanged at mid-century, with only slight decreases in both evident 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.

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

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