EnvironmEntal SciEncES | Climatology
Impact of ENSO
on extreme temperatures
in
Vietnam
Duc Ngu Nguyen*
Centre for Hydro-Meteorological and Environmental Sciences and Technologies
Received 25 May 2017; accepted 30 October 2017
Abstract:
in
the
frequency
distribution
and
This paper presents the results of research on the effects of ENSO to extreme
intensity of climatic extremes that affect
temperature in Vietnam [1] through the frequency deviation of the occurrence
production, and more importantly, can
extreme temperatures during ENSO and non-ENSO seasons. The results
cause
severe
natural
disasters
such
demonstrate that in an El Niño winter, the frequency of absolute maximum
as
heat
waves,
cold
weather,
floods,
temperature decreased over mountainous areas of the temperature in
prolonged
droughts,
unusually
strong
comparison to those under the influence of a non-ENSO winter. In summer,
the effects of El Niño and La Nina generally led to a reduction in the frequency
of maximum temperatures in comparison to the non-ENSO condition. For
minimum temperatures, the effect of El Niño winter led to a decrease in the
appearance of the temperatures, while the effect of La Nina led to an increase
in the appearance of this characteristic. In contrast, the effects of El Niño
and La Nina led to a reduction in the frequency of minimum temperatures
during summer. Generally, in both El Niño and La Nina conditions, significant
changes were observed in the distribution of frequency deviation with regard
to both patterns and values of seasons, in which the South obviously exhibited
typhoons, among others.
This study investigates the
distribution of extreme temperature
in the seasons of El Niño (E), La Nina
(L), and non-ENSO (N) during winter
and summer across regions spread
throughout the country. The impacts
of ENSO on extreme temperatures
in Vietnam have been assessed, an
more changes than the North.
evaluation that facilitates the creation of
Keywords: effects of ENSO, extremes temperature, winter.
forecasting and early warning methods
that can contribute to the prevention and
Classification number: 6.2
reduction of damage caused by natural
disasters.
Data and methods
Data
Introduction
Research on weather and climate
extremes is of particular importance for
both scientific and practical purposes.
Most climate extremes occur under
conditions of abnormal variability in
terms of atmospheric circulation or
solar radiation. In the context of global
climate change, some of the weather
to occur more frequently in the 21st
century [2]. In fact, the variation in
extreme weather and climate has been
exhibited in many places; further, even
the moderating climate of local climate
conditions also causes to extreme
changes [3]. The climate extreme has
occurred increasingly more, especially
the El Niño and La Nina (ENSO)
To investigate the distribution of
extreme temperature, we have utilized
the average maximum and minimum
temperature and monthly absolute
maximum and minimum temperature
data from 38 meteorological stations
from the period 1961-2000 and ENSO
data from the period 1951-2000.
Methods
and climate extreme events are likely
phenomenon [4] that effects a change
The periods of ENSO (El Niño and
*Email: nguyenducngu@yahoo.com.
December 2017 Vol.59 Number 4
Vietnam Journal of Science,
Technology and Engineering
89
p
EnvironmEntal SciEncES | Climatology
La Nina) that occurred during the period
temperature in non-ENSO seasons).
Results and discussions
1951-2010 are determined with red to
the following regulations:
Determine the extreme temperature
values for the 95th, 90th, 5th, and 10th
For the above definition, the years
and seasons of El Niño (N), La Nina
-
El
Niño
(La
Nina)
forms
a
percentile
utilized
as
the
“threshold”
(L), and non-ENSO (N) are presented
continuous
period
of
no
less
than
6
values of the “warm” (“cold”) events
in Table 1
months with a 5-month moving average
of the monthly mean sea surface
temperature anomalies in NINO.3 (5oN-
5oS, 150oW-90oW) that is greater than
or equal to 0.5oC (less than or equal to
- 0.5oC) [3].
- Define months and seasons as (3
months) El Niño (E), La Nina (L), and
non-ENSO (N):
From the El Niño and La Nina periods
defined as above, the months E, L, and
N are determined. To determine the
ENSO seasons (El Niño and La Nina),
each season is defined as constituting
3 months, wherein the spring stretches
from March to May, summer from June
to August, Autumn from September to
November, and winter from December
to February, while the average sea
surface temperature anomaly (SSTA) in
the NINO.3 area is in accordance to the
following criteria:
SSTA ≥ 0.5oC El Niño (E)
- 0.5oC ≤ SSTA< 0.5oC neutral or non-ENSO (N)
with the following rules: The “extreme”
events occur when maximum/minimum
temperature in the ENSO seasons are
higher (lower) than the “threshold”
values that correspond to the 90th, 95th
(5th, 10th) percentile for the non-ENSO
(normal) seasons.
- Calculate the frequency of
occurrence of extreme temperatures
in ENSO seasons, with the extreme
temperature as higher (lower) than the
“threshold” of extreme temperatures
with percentiles 90th, 95th (5th, 10th) in
non-ENSO seasons of the corresponding
seasons.
- Calculate the frequency deviation
(Panom) of extreme temperatures in ENSO
seasons that correspond to the percentiles
90th, 95th (5th, 10th) (“threshold”) in
non-ENSO seasons of the corresponding
seasons through the application of by the
formula given below [5]:
Panom = 100(100 m 1)
Mean winter, summer of E, L,
N seasons’ extreme temperature
distribution (spring and autumn cases
are omitted)
Monthly average maximum
temperature (Tx ):
- Winter:
In the North-West, the values of
monthly Tx in E seasons were found to
be higher in N and L seasons with 0.5-
2oC. The difference between the highest
value and the lowest value of the average
monthly maximum temperature (x) in
E and L seasons was determined to be
nearly 8-10oC, values that are
comparatively lesser than that in N
seasons (about 12oC).
In the North-East, monthly Tx in E
seasons was found to be greater than that
in L seasons, but at the same level as that
of N seasons. In contrast, the maximum
value of monthly Tx in E seasons was
found to be greater than L and N seasons
of 2-3oC, while the minimum value for
SSTA < - 0.5oC La Nina (L)
where:
the monthly Tx in E seasons was
determined as being greater than that in
Each season must comprise at least
p forms the frequency of extremes for
L seasons and less than that in N seasons
two consecutive months to satisfy one
ENSO seasons higher (lower) than the
of about 1-2oC. x in E seasons is 10-
of the above provided criteria. In the
case where there are no two consecutive
months that fulfill the above criteria,
the average SSTA of 3 months must
meet that criterion. The frequency and
frequency deviation of temperature
extremes in ENSO (El Niño, La Nina),
and non-ENSO seasons are calculated as
follows:
“threshold” values for the m percentile
in the non-ENSO seasons (base seasons)
of the corresponding seasons;
m represents the number of percentiles.
Thus, the frequency anomaly reflects
the increase or decrease in the frequency
of extremes during ENSO seasons
in comparison to their occurrences
11oC higher than that in L seasons (9-
10oC) and N seasons (7-9oC).
In North central and South central
regions, monthly Tx in E seasons was
found to be higher in N and L seasons,
especially in the North central region (2-
5oC) (in the South central, it was only
0.5-1oC). x in E seasons in the North
central reached 9-10oC, while for N and
- Calculates the 5th, 10th, 25th, 50th,
during
non-ENSO
seasons
for
the
L seasons it was only 7-8oC. In the South
75th, 90th, 95th percentile of the extreme
corresponding seasons.
central
region,
the
value
of
this
90
Vietnam Journal of Science,
Technology and Engineering
December 2017 Vol.59 Number 4
EnvironmEntal SciEncES | Climatology
Table 1. ENSO (E, L) and non-ENSO (N) seasons in the period 1950-2000.
Spring (III-V)
Summer (VI-VIII)
Autumn (IX-XI)
Winter (XII-II)
E
L
N
E
L
N
E
L
N
E
L
N
1953
1950
1951
1951
1954
1950
1951
1954
1950
51/52
49/50
50/51
1957
1954
1952
1953
1955
1952
1953
1955
1952
57/58
64/65
52/53
1958
1955
1956
1957
1964
1956
1957
1964
1956
63/64
67/68
53/54
1969
1964
1959
1963
1970
1958
1963
1967
1958
65/66
70/71
54/55
1972
1968
1960
1965
1971
1959
1965
1970
1959
68/69
73/74
55/56
1982
1971
1961
1969
1973
1960
1968
1971
1960
69/70
75/76
56/57
1983
1985
1962
1972
1975
1961
1969
1973
1961
72/73
84/85
58/59
1987
1988
1963
1976
1985
1962
1972
1975
1962
76/77
85/86
59/60
1991
1999
1965
1979
1988
1966
1976
1984
1966
79/80
88/89
60/61
1992
1966
1982
1999
1967
1979
1985
1974
82/83
98/99
61/62
1993
1967
1983
1968
1982
1988
1977
86/87
99/00
62/63
1997
1970
1987
1974
1986
1998
1978
87/88
66/67
1998
1973
1991
1977
1987
1999
1980
91/92
71/72
1974
1993
1978
1991
1981
97/98
74/75
1975
1997
1980
1997
1983
77/78
1976
1981
1989
78/79
1977
1984
1990
80/81
1978
1986
1992
81/82
1979
1989
1993
83/84
1980
1990
1994
89/90
1981
1992
1995
90/91
1984
1994
1996
92/93
1986
1995
2000
93/94
1989
1996
94/95
1990
1998
95/96
1994
2000
96/97
1995
00/01
1996
2000
e: el Niño, l: la Nina, N: non-eNSo.
December 2017 Vol.59 Number 4
Vietnam Journal of Science,
Technology and Engineering
91