ENSO’S IMPACTS ON CLIMATE,

WEATHER, EMVIRONMENT, AND

SOCIO-ECONOMIC DEVELOPMENT IN

VIETNAM

Prof. Dr. of Sciences Nguyen Duc Ngu

Center for Hydro – Meteorological and Environment Science and Technology

(CHMEST)

Strips of clouds in El Nino in December, 1997 and La Nina in December, 1998

INTRODUCTION

• Definitions of ENSO.

- El Nino

- La Nina

- ENSO

• Importance of research on ENSO.

I. OVERVIEW OF PHYSICAL MECHANISM OF ENSO

1.1 Trade wind, Southern Oscillation and Walker circulation. (Figure 1.1)

- Pacific Ocean’s East and West air pressure gradient- Lower and higher-layer wind in Pacific Equatorial region.- Walker circulation.1.2 Sea water's temperature, upward-water movement and

thermo cline in Pacific Equatorial region. (Table 1.1)- East - West temperature gradient- Upward-water movement and thermo cline

EquatorEast-directing wind

Trade wind Northern semisphere

Trade wind in Northern semisphere

West-directing wind

Walker circulation

Evaporative exchange

Precipitation

Figure 1.1: Diagram of Walker circulation in a normal condition

thermo cline

800West1200East cont.

Hot, low pressureCold, high pressure

upward-water movement

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Table 1.1: Average monthly and yearly sea surface water's temperature in NINO-affected Region (0C) (period of 1961 – 1990)

Month

Region D (Warm pool)

140N – 00, 1300E-1500E

Region A (~ Nino.4)

40N – 40S, 1500E-1500W

Region B (~ Nino.3)

40N– 40S, 1500W-900W

Region C (~ Nino 1+2)

00 – 140S, 900W-800W

1 28.5 28.0 25.4 24.3

2 28.3 28.0 26.2 25.7

3 28.4 28.1 26.9 25.9

4 28.8 28.2 27.1 25.1

5 29.5 28.3 26.6 23.9

6 29.3 28.4 26.1 22.7

7 29.2 28.5 25.2 21.6

8 29.1 28.4 24.6 20.6

9 29.2 28.3 24.6 20.3

10 29.3 28.4 24.6 20.7

11 29.2 28.4 24.6 21.5

12 28.9 28.2 24.9 22.6

Year 29.0 28.3 25.6 22.9 Trở về

I. OVERVIEW ABOUT ENSO’S PHYSICAL MECHANISM

1.3 Ocean - atmosphere interaction - Deep exchange and atmospheric cyclones

are reflected through accumulation of directing winds and Outgoing Long wave Radiation (OLR).

- Ocean-atmosphere vertical exchange: components of heat and moisture.

1.4 ENSO’s operational mechanism- Walker circulation in a normal condition (Figure 1.1)- Development process and roles of Kelvin and Rossby oceanic

waves.- Walker circulation in El Nino condition and operations of

evaporative exchange in Pacific Ocean Equator region (Figure 1.2)

- Walker circulation in La Nina condition.- Unstable factors that have impacts on Walker circulation and

ENSO (Pacific sub-tropical high pressure, intensification of West-directing wind in the Western Pacific Equator region, MJO, tropical cyclones). (cont.)

I. OVERVIEW ABOUT ENSO’S PHYSICAL MECHANISM (cont.)

EquatorWeak East-directing wind

Weak Trade wind in Northern semisphere

Weak Trade wind in Northern semisphere

West-directing wind

Restrained exchange

Restrained exchange

Figure 1.2: Diagram of Walker circulation in El Nino condition

800W1200E

Thermo cline

Intensified West-directing wind

East-directing wind

Walker circulationEvaporati

ve exchange

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Hot, low pressure

Cold, high pressure

Weak Upward-water movement

Decreased depth of thermo cline

I. OVERVIEW ABOUT ENSO’S PHYSICAL MECHANISM (cont.)

1.5 ENSO’s indicators and El Nino and La Nina periods (1950 – 2005)

Indicators Region NINO.3 (50N – 50S, 1500W -900W)

- El Nino: 5 Months ≥ 0,50C (Table 1.2)

- La Nina: 5 Months ≤ - 0,50C (Table 1.3)

- Duration ≥ 6 Months

SSTA

SSTA

Table 1.2: Hot ENSO period (El Nino)* Underlined periods are the strong El Nino

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No. El Nino Month of

commencementMonth of disintegration

Duration Maximal SSTA (0C) and occurring month

1 1951/1952 6/1951 1/1952 8 1.3 10/1951

2 1953 3/1953 11/1953 9 1.1 9/1953

3 1957/1958 4/1957 5/1958 14 1.8 12/1957

4 1963/1964 6/1963 2/1964 9 1.2 12/0963

5 1965/1966 5/1965 2/1966 10 1.8 12/1965

6 1968/69/70 9/1968 2/1970 18 1.4 12/1969

7 1972/1973 4/1972 3/1973 12 2.6 12/1972

8 1976/1977 6/1976 2/1977 9 1.2 9,10/1976

9 1979 7/1979 12/1979 6 1.2 9/1979

10 1982/1983 4/1982 9/1983 18 3.6 1/1983

11 1986/87/88 9/1986 1/1988 17 2.0 9/1987

12 1991/1992 4/1991 6/1992 15 1.7 1/1992

13 1993 2/1993 8/1993 7 1.5 5/1993

14 1997/1998 4/1997 6/1998 15 3.9 12/1997

15 2002/2003 7/2002 1/2003 7 1.4 11,12/2002

No. La Nina Month of

commencementMonth of

disintegrationDuration

Maximal SSTA (0C) and occurring month

1 1949/1950 End 1949 4/1950 -1.7 2/1950

2 1954/55/1956 5/1954 2/1956 22 -2.0 11/1955

3 1964/1965 4/1964 1/1965 10 -1.2 12/1964

4 1967/1968 9/1967 4/1968 8 -1.3 2/1968

5 1970/1971 6/1970 12/1971 19 -1.5 12/1970

6 1973/1974 6/1973 3/1974 10 -1.4 1/1974

7 1975/1976 4/1975 3/1976 12 -1.5 12/1975, 1/1976

8 1984/1985 10/1984 12/1985 15 -1.2 12/1984

9 1988/1989 4/1988 3/1989 12 -1.7 11,12/18

10 1998/99/2000 10/1998 3/2000 18 -1.6 1/2000

Table 1.3: Cold ENSO period (La Nina)* Underlined periods are the strong La Nina

1.6 Characteristics of distribution and operation of El

Nino and La Nina1/ In 55 years (1951 – 2005), there were:

- 15 El Nino periods, of which:

+ Longest period (1968 - 1970 and 1982 - 1983): 18 months.

+ Shortest period (1979): 6 months.

+ Average duration per period: 12 months.

- 10 La Nina periods, of which:

+ Longest period (1954 - 1956): 22 months.

+ Shortest period (1967 - 1968): 8 months.

+ Average duration per period: 13 months.

- 6 times of 2 consecutive El Nino periods but only 1 time of 2

consecutive La Nina periods.

1.6 Characteristics of distribution and operation

of El Nino and La Nina (cont.)2/ 8 strong El Nino periods (average SSTA per month ≥ 1.50C)

6 strong La Nina periods (maximal SSTA in a month ≤ -1.50C)

3/ Most of ENSO started in spring (March - May), mostly in April,

and ended in winter or spring (December - April).

No strong El Nino period started in the middle of winter or summer.

No strong La Nina period started in the middle of winter.

1.6 Characteristics of distribution and operation of El

Nino and La Nina (cont.) 4/ Strongest stage (maximum) of each ENSO period is the middle of winter

(December - January).

5/ Each ENSO period is clearly phased into 7 stages and each stage lasts

for 2 - 3 months

stage of pre-commencement.

stage of commencement.

stage of development.

stage of transition.

stage of maximum.

stage of declination.

stage of disintegration.

II. ENSO's impacts on weather AND climate IN VIETNAM

2.1 ENSO's impacts on frequency of cold fronts in Vietnam

- Frequency of cold fronts in Hanoi (1956 - 2000)

Table 2.1: Frequency of cold fronts in Hanoi (1956 - 2000)

Month 1 2 3 4 5 6 7 8 9 10 11 12 Year

Average 4.0 3.2 3.3 2.7 2.7 1.5 0.13 0.16 1.4 2.9 3.6 3.5 29.1

Standard deviation

1 2 3 4 5 6 7 8 9 10 11 12 Total Ratio

El Nino

Positive 7 4 1 2 5 7 2 1 7 9 9 6 600.7

Negative 4 7 7 10 8 6 11 12 7 4 4 7 87

La Nina

Positive 0 2 2 3 5 3 0 4 4 7 4 8 420.7

Negative 4 6 6 5 2 6 8 4 5 4 7 3 60

Table 2.2: Standard deviation of frequency of cold fronts in Hanoi during El Nino and La Nina months (1956 – 2000)

2.1 ENSO's impacts on frequency of cold fronts in Vietnam-Frequency of cold fronts in El Nino and La Nina conditions (Table 2.2):

Generally, total Positive standard deviation of the whole year is always lower than total Negative standard deviation of the whole year, mainly decreasing at the end of winder and summer months

Table 2.3: Frequency of storms per month and year that have direct impacts on Vietnam (1956-2000)

Month 1 2 3 4 5 6 7 8 9 10 11 12 Yearstorm season

storm month

frequency

0 0 0.1 0.1 0.1 0.7 0.7 1.2 1.4 1.3 1.0 0.3 6.9 6.6 0.95

2.2 ENSO's impacts on operations of storms in Vietnam

* Average frequency of storms (1956 – 2000)- Average per year: 6.9 storms- Average per storm season (June – December): 6.6 storms- Average per storm month: 0.95 storms

* Operations of storms in El Nino condition (Table 2.4)

- Average per El Nino months: 0,4 storms (less than in a normal condition ~ 28%)

- Average per the whole storm season of El Nino period : 4.8 storms (less than in a normal condition ~ 28%)

- Average in 1 storm month of El Nino period: 0.69 storms (less than in a normal condition ~ 27%)

2.2 ENSO's impacts on operations of storms in Vietnam

El Nino period

IV V VI VII VIII IX X XI XIINo. of storms

Ratio (No. of storms per month

E)From UntilDuration (Month)

IV/57 IV/58 14 1 1 2 2/14

VI/63 II/64 9 1 4 2 7 7/9

V/65 II/66 10 1 2 1 1 5 5/10

IX/68 II/70 18 2 1 3 2 8 8/18

IV/72 III/73 12 1 1 3 2 7 7/12

VI/76 II/77 9 0 0/9

VII/79 XII/79 6 2 1 1 4 4/6

IV/82 IX/83 17 1 1 2 1 5 5/18

IX/86 I/88 18 2 3 3 2 2 12 12/17

IV/91 VI/92 15 1 1 1 1 2 6 6/15

II/93 VIII/93 7 1 1 2 4 4/7

IV/97 VI/98 15 1 1 1 3 3/15

Total 150 1 5 9 16 16 5 5 6 63 63/150

Table 2.4: Storms that have direct impacts on Vietnam during El Nino period

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2.2 ENSO's impacts on operations of storms in Vietnam

* Operations of storms in La Nina condition (Table 2.5)

- Average per La Nina Month : 0.8 storms (higher than in a normal condition ~ 38%, double in 1 El Nino month)

- Average per the whole storm season in La Nina period: 9.17 storms (higher than in a normal condition ~ 27%, higher than in a storm season of a El Nino period: 91%)

- Average per 1 storm of La Nina month: 1.31 storms (higher than in a normal condition ~ 27%, higher than in 1 storm month of El Nino period: 90%)

La Nina period

V VI VII VIII IX X XI XIINo. of storms

Ratio (No. of storms per Month

L)From UntilDuration (Month)

IV/64 I/65 10 1 1 3 3 3 11 11/10

IX/67 IV/68 8 1 2 1 4 4/8

VI/70 XII/71 19 1 2 3 1 2 4 5 18 18/19

VI/73 III/74 10 1 2 5 2 2 12 12/10

IV/75 III/76 15 1 2 2 3 1 9 9/15

X/84 XII/85 15 1 2 3 5 1 12 12/15

IV/88 III/89 12 3 2 5 5/12

X/98 III/2000 18 1 1 1 1 2 3 3 3 15 15/18Total 107 2 5 6 9 18 25 16 5 86 86/107

Table 2.5: No. of storms affecting on in Vietnam during La Nina period

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StationLang Son

Son La Hanoi Vinh Da Nang Pleiku Can ThoTan Son

NhatAverage

El Nino 1.4 1.5 1.2 1.2 1.8 1.3 1.6 2.0 1.5

La Nina 0.7 0.5 0.7 0.7 0.6 0.6 0.6 0.7 0.6

2.3 ENSO's impacts on temperature

Table 2.6: Ratio between total Positive and Negative standard deviations of average temperature per month during

El Nino and La Nina periods in some locations (1960-2000)

- During most of El Nino months all regions have positive standard deviation, which is higher than negative standard deviation (Ratio ranging from 1.2 to 2.0).- During most of La Nina months all regions have positive standard deviation, which is lower than negative standard deviation (Ratio ranging from 0.5 to .7)

- However, besides during some El Nino periods, the absolute lowest temperature was recorded, and during some La Nina periods, the absolute highest temperature was recorded

StationLang Son Son La Hanoi Vinh Da Nang Pleiku Can Tho

Tan Son Nhat

El Nino

TX

(Month/Year)

37.6 (7/83) 36.3 (3/98)39.4 (6/83)39.6 (6/98)

40.0 (5/98) 40.1 (6/98)38.9

(5/98)36.0

(4/98)39.3 (5/98)

Tm (Month/Year

)

5.4 (1/77)10.6

(11/79)13.1 (2/77) 8.6 (2/77)

16.5 (12/63)

La Nina

TX

(Month/Year)

39.5 (6/99) 40.0 (5/88)37.3

(3/99)39.7 (1/99)

Tm (Month/Year

)

-1.7 (2/68)-1.5 (12/75)

-0.2 (12/75) 5.0 (2/68)5.9 (1/74)

5.1 (12/99)9.4 (12/99)10.2 (1/74)

6.1 (12/75)

14.8 (1/63)

Table 2.7: Some absolute maximum (Tx) and minimum (Tm) record temperatures during

El Nino and La Nina period (0C)

2.4 ENSO's impacts on rainfall

* Criteria for evaluation:

+ A reduction of rainfall in 1 ENSO period is defined as a

subtraction between the actual rainfall in each period of El

Nino (La Nina) and the total of average rainfall of many years

within the same period, same point of time. The reduction is

represented by %.

* Results:+ Most of El Nino periods caused a reduction in

rainfall in most of areas of the country, average reduction per period: 20 – 50%. The higher reduction in 1 El Nino period: 69% in Buon Ma Thuot

+About a half of La Nina period caused a reduction in rainfall in areas, mostly in Northern and Central Highland Regions, average reduction per period:15 – 20%. The higher reduction in 1 La Nina period: 47.2% in Nha Trang. However, total La Nina periods that cause a reduction in rainfall is as many as total La Nina periods that cause a surplus in rainfall, mainly in Coastal Central and South Western regions (Table 2.8)

* The figure in ( ) is the average of total El Nino and La Nina periods under review

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Table 2.8: Reduction in rainfall during ENSO months in some locations

CharacteristicsVinh Da Nang

Nha Trang

Phan Thiet

Plei KuBuon Ma

ThuotDa Lat Remarks

Number of El Nino periods causing a reduction in rainfall out of 11 periods under review

6/11 8/11 9/11 10/11 7/11 10/11 8/11

Average reduction in rainfall per El Nino period (%)

22.6 (12.4)

17.6 (12.8)

24.1 (19.7)

13.4 (12.2)

17.4 (11.1)

21.7 (19.7)

19.0 (13.8)

the figure in ( ) is the average

figure of total 11 El Nino periods

under review

Number of La Nina periods causing a reduction in rainfall out of 8 periods under review

3/8 3/8 1/7 5/8 5/8 3/7 3/7

Average reduction in rainfall per La Nina period (%)

15.0 (5.6) 19.2 (7.2) 47.2 (5.9) 17.0 (10.6)

18.0 (11.3)

20.9 (8.9) 9.7 (5.5) the figure in ( ) is the average

figure of total 8 La Nina periods

under review

Table 2.9: Some maximum records in rainfall (Rx) occurring during El Nino and La Nina periods (mm)

Station Lang Son Son La Hanoi Vinh Da Nang Can ThoTan Son

Nhat

El NinoRx

(Month/Year)162 (5/82)128(9/86)

161 (7/91)126 (9/69)81 (5/73)

206 (8/72)118 (9/83)

116 (11/86)131 (8/83)

113 (10/91)

La NinaRx

(Month/Year)202 (7/71)123 (3/98)

135 (8/99) 395 (11/84) 388 (9/85)393

(11/99)105 (10/98) 134 (11/98)

2.5 ENSO's impacts on salinity in coastal areas and islands of Vietnam.

In general, El Nino increased the salinity; in contrast, La Nina reduced the salinity of Sea water in the coastal areas and islands of Viet Nam.

• 2.6 ENSO's impacts on the flow of rivers in Vietnam.

• In the years under the impact of El Nino, the annual flow of rivers was lower by over 10% than the average of many years.

• In the years under the impact of La Nina, the annual flow of rivers was usually higher by 80 – 100% than the average of many years;

• In the years under the impact of El Nino, the flow was lower than the average flow of many years, the ratio (%) between the flow of flood season and the average flow of many years reached by 65 – 95 %;

• In the years under the impact of La Nina, this ratio reached by 101 – 110% and even by 130 – 140% in some regions.

• In the years under the impact of El Nino, the minimum flow of rivers in 3 consecutive months is as much as 80%-90% of the average flow of many years;

• In contrast, in the years under the impact of La Nina, the flow was higher by 101 – 140 % than the average value of many years.

3.1 ENSO's impacts on output of hydroelectricity.The relationship between the average water flow per year with the annual output of four hydro power plants including Hoa Binh, Thac Ba, Tri An, Da Nhim was in the direct proposition with the correlation rate of 0.5 – 0.8. Therefore, it is notable that ENSO had the impact on the reduction of the output for the hydroelectricity. Meanwhile, the impact of La Nina facilitated the increase in output of the above-mentioned hydro power plants.

III. ENSO's impacts on SOME ECONOMIC SECTORS

3.2 ENSO's impacts on agricultural production.

- In the condition of El Nino, the average turnover of the spring harvest reduced

comparing with the previous harvest, especially for the Midland in Northern Viet

Nam; in contrast, the output of the autumn harvest increased, especially for the

Northern Central region.

- In the condition of La Nina, the average output of the spring and the autumn

harvest also increased than the previous harvests.

- In the condition of ENSO, the area of coffee plant that could be harvested and

the output of coffee bean also increased comparing with the previous harvest;

in the years under the impact of La Nina, the area of coffee plant was higher

than in the years under the impact of El Nino, but the output of coffee bean in

the years under the impact of El Nino was higher in the years under the impact

of La Nina.

3.3 ENSO's impacts on life and health of human

being.

- Since 1977 until 2000, the total number of dead and missing people caused

by the natural disaster was 14,962 people; of which 64 % of cases occurred

in the years under the impact of ENSO (El Nino 43%, La Nina 21%).

- The prevalence of petechial fever reached 100,000 cases in the period of

1976 – 1998 in relation to El Nino phenomenon with the correlation rate from

0.4 – 0.6. Only within a period of El Nino from 1997 – 1998, the petechial

fever occurred in 51 provinces and cities of Viet Nam with the average rate of

306 cases/100,000 people.

Some statistics-based forecast models for seasons (3 months) are developed based on information and data of ENSO applicable to some factors and hydrological phenomenon as follows:- Frequency of tropical cyclones in South China Sea and Vietnam.- Average and maximum air temperature.- (Total and maximum) Rainfall.- Flows of running water in some locations in the Red River basin.- Draughts.

IV. CAPACITY FOR PREDICTION OF ENSO's impacts

Besides measures for irrigation, protection forests, coastal protection, etc., non-infrastructure-based measures are as follows:1. Integrated planning and management for water basin and water reservoirs.2. Transformation of cropping patterns and structures in some regions to adapt to ENSO's impacts.

V. SOME MEASURES TO MITIGATE ADVERSE IMPACTS AND DAMAGES

CAUSED BY ENSO

3. Develop and finalize measures to monitor, predict, and warn about ENSO's impacts.4. Intensify disaster management of the Government and agencies for ENSO's impacts as a part of the National Strategy on Sustainable Development.5. Continue to intensify propaganda and awareness raising for the public on ENSO and mitigation measures.

V. SOME MEASURES TO MITIGATE ADVERSE IMPACTS AND DAMAGES

CAUSED BY ENSO (cont.)

- ENSO (El Nino, La Nina) has had discernible impacts on weather and climate of our country, and sometimes caused abnormal climate phenomenon, especially for the last 2 decades

- ENSO's impacts on weather and climate of our country are very complicated, various but it is possible to identify a general trend of impacts in El Nino or La Nina.

- Based on understanding on mechanisms and rules of ENSO's impacts and its consequences on weather and climate, we are able to provide early warning so that effective mitigation measures are developed to encounter with negative impacts caused by ENSO as well as develop long-term, strategic planning for sustainable socio-economic development.

VI. CONCLUSIONVI. CONCLUSION

THANK YOU.