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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
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1500
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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
LOWER GREENHOUSE GAS SCENARIO (RCP4.5)
+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
HIGHER GREENHOUSE GAS SCENARIO (RCP8.5)
+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).
H I G H - R ESO LUT I O N CL I MATE PROJ ECT I O N S FO R V I ETNAM4
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
GCM TIMESERIES—RCP 8.5 (HIGHER)
TEM
PER
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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
26
28
30
32
34
SOUTH WEST MONSOON SEASON (JUN–SEP)
N O RTH WEST 5
22
24
26
28
TIME
GCM TIMESERIES—RCP 8.5 (HIGHER)
TEM
PER
ATU
RE
(°C)
CHA
NG
E IN
TEM
PER
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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
SECOND INTER-MONSOON SEASON (OCT–NOV)
18
20
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TIME
GCM TIMESERIES—RCP 8.5 (HIGHER)
TEM
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E IN
TEM
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(°C)
CO
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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
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.
H I G H - R ESO LUT I O N CL I MATE PROJ ECT I O N S FO R V I ETNAM6
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
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TIME
FIRST INTER-MONSOON SEASON (APR–MAY)
GCM TIMESERIES—RCP 8.5 (HIGHER)
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)
END OFCENTURYSUMMARY
1900 1950 2000 2050 2100
GCM
RCM
GCM
RCM
150
200
250
300
350
400
450
−40
−20
0
20
40
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80
TIME
SOUTH WEST MONSOON SEASON (JUN–SEP)
GCM TIMESERIES—RCP 8.5 (HIGHER)
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)
END OFCENTURYSUMMARY
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)
GCM TIMESERIES—RCP 8.5 (HIGHER)
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)
END OFCENTURYSUMMARY
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)
END OFCENTURYSUMMARY
GCM TIMESERIES—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.
H I G H - R ESO LUT I O N CL I MATE PROJ ECT I O N S FO R V I ETNAM8
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
LOWER GREENHOUSE GAS SCENARIO (RCP4.5)
-16 to +12 -7 to +27 -17 to +12 -22 to +19 -28 to +57
HIGHER GREENHOUSE GAS SCENARIO (RCP8.5)
-10 to +3 -26 to +19 -18 to +16 -15 to +10 -28 to +13
2080–2099
LOWER GREENHOUSE GAS SCENARIO (RCP4.5)
-14 to +7 -22 to +57 -12 to +2 -23 to +14 -32 to +55
HIGHER GREENHOUSE GAS SCENARIO (RCP8.5)
-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