AN OVERVIEW OF SOME EXTREME WEATHER PHENOMENA
AND SOCIO AND ECONOMIC IMPACTS IN VIET NAM
Prof.Dr. Tran Tho Dat1, Assoc. Prof.Dr. Dinh Duc Truong1, Dr. Nguyen
Dang Quang 2, Dr. Doan Quang Tri 2, MA. Huynh Thi Mai Dung1
1
National Economics University, Hanoi Vietnam
2
Vietnam Meteorological and Hydrological Administration
Abstract
Extreme weather includes unexpected, unusual or unseasonal weather, weather at
the extremes of the historical distribution. Often, extreme phenomena are based on a
location‟s recorded weather history and defined as lying in the most unusual percent. In
recent years some extreme weather phenomena have been attributed to the humaninduced global warming with a number of studies indicating an increase of natural, social
and economic threats from extreme weather. This paper attempts to overview some
extreme weather phenomena in Vietnam over recent years, present their social and
economic impacts, and to recommend policy implications.
Keywords: Extreme weather, climate change, natural disaster damages, social and
economic impacts.
1. Introduction
Vietnam is one of the most severely affected countries by natural disasters and
extreme weather in the Asia-Pacific region due to its geographical location and
topography. In recent years, under the impact of climate change, extreme natural disasters
have occurred more frequently, causing human losses and significant impacts on the
economy. According to IMHEN and UNDP (2015), from 1990 to 2010, 74 floods occurred
in the river systems of Vietnam, severe droughts, salinity intrusion, landslides and other
natural disasters have also been hindering the development of Vietnam. In the past 20
years, Vietnam has suffered more than 800 natural disasters (an average 40 disasters/year)
with increasing intensity and frequency causing great damages to economic, social and
ecological dimensions, especially during 2005-2015 (WMO). Currently, Vietnam suffers
annual losses of 1.4-1.8% of GDP annually due to natural disasters phenomena. The
economic consequences are not only in the short term but also in the medium and longterm including reduced economic growth, employment, income, investment and trade. This

paper tries to overview some extreme weather phenomena in Vietnam over recent years
and their social and economic impacts, then some policy implications will be drawn.
2. Theoretical framework
In theory, a climate variable is considered to be a random variable with a value
changing within a certain limit. This limit may be blocked or not blocked, on one side or both.
A weather variable is called extreme if its value domain centers on one side of the
possible set of weather variables being considered. For example, the temperature in the air

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(at some point in time) is an atmospheric variable. Its value range can range from the
smallest a0 to b0. Every day has a minimum value (minimum daily temperature) and a
highest value (maximum daily temperature). The set of all minimum (maximum) daily
temperature values is considered to be the set of possible values of a random quantity
called the minimum (maximum) factors (or extreme climatic factors). Then, the minimum
temperature will be in the range or range from a0 to a1, while the maximum temperature
will vary from b1 to b0, with a0 ≤ a1 and b1 ≤b0.
Let X is a particular climatic variable with the distribution function F(x), or the
probability density function F(x). Then, the set of x values of X satisfying the following
condition is called the extreme set of values for X, or extreme climate:
{
{

|

} (1) or

|


} (2) with
=∫

P = P(X<

)=F(

P = P(X

)=1-F(

(3) or

=∫

(4)

That is, the probability of occurrence of events X<

or X

=p

When studying extreme elements and climatic phenomena, people often pay
attention to its extreme values and call it extremist climatic extremes. Extreme climatic
factors are defined as the values of extreme weather variables with a probability of
occurring less than or equal to 10%. However, each locality or region has different
application. For example, one can reduce the probability of appearing to 5% or even 1%, or
increasing p to 15%, 20%, or even to 25% or 30%.
In many cases, for simplicity, instead of using the notion of probability, one can use

the concept of percentile. The extreme climatic variables considered are usually the
maximum or minimum climate variables. If it is a minimum climate, the values smaller
than the q centimeter (for 100 centigrade) are considered extreme, and for the extreme
climatic factors, values greater than q is considered extreme.
The qth subdivision of the random variable X is the x value of X that satisfies the
condition:
[

]

In other words, the solution of f (x) = q%. For the minimum climate, q (%) = p (%)
and for the maximum climate variables q (%) = 1 - p (%).
In order to avoid confusion, attention should be paid to distinguishing the concept
of the radical with the absolute concept of the absolute term of many years which is often
referred to as the record of values.
3. An overview on some extreme weather phenomena in Vietnam
There have been accelerated developments in weather and extreme natural hazards
due to climate change recently. The intensity, time span and place of occurrence of these
phenomena are no longer stick to conventional climate patterns. The catastrophic floods

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have been recorded in the North, heat waves and severe droughts have been seen in the
Central region, especially in the South, where traditionally known as temperate climate,
have been suffering the lack of fresh water and serious saline intrusion. In this paper, we
try to synthesize and analyze the evolution of dangerous meteorological phenomena,
namely heat wave, drought, substantial rain and typhoon.
a. Heat wave
In the past 40 years, the average national temperature in each decade has increased

at a rate of 0.26 ± 0.100C, which has been two times higher than the pace of global
temperature rise in the same timescale (Nguyen Dang Quang et al. 2013). According to the
research, the increase in winter temperature was greater than that in summer temperature,
and the average temperature increase in the South was greater than that in the North (Fig.
1). In the South, while the lowest temperature at night (Tmin) in the winter has increased
significantly than the maximum temperature in the daytime (Tmax), in several places in the
South and islands, the opposite is true. As a result, fierce heat waves have been increasingly
observed in the North and this phenomenon has been verified through measured data. Phan
Van Tam et al. (2010) demonstrated that the number of hot days tended to increase at a
national level from 1961 to 2007, and these figures even increased more (approximately
10%) between 1991 and 2007 at stations in the North East, the Northern Delta and the North
Central Coast, in which the North Central Coast was the area having a majority of hot days
(Fig. 2). The hot days on average of this area fluctuated from about 40 to 60 days per year, of
which the highest number of hot days was 90 (Nam Dong station) and the lowest one was 20
(Thanh Hoa station). Apart from two coastal stations (Nha Trang, Phan Thiet), the number of
hot days in South Central was similar to that in North Central Coast.

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Fig.1. Standard deviation of average temperature over the climate zones of Viet
Nam from 1971 to 2010. N1 - N4, S1 - S3: the northern and southern climate. The bold
lines showed standard deviations of temperature on June, July, August, December, January
and February; the light lines illustrated standard deviations of temperature on May, June,
July, November, December and January; dotted lines represented standard deviations of
temperature on August, September, October, January, February and March (Nguyen Dang
Quang et al., 2013).
100

80

Số ngày nắng nóng

B4
60

40

N1
B1
B2

0

B3

N2
N3

Điện Biên
Lai Châu
Sơn La
Bắc Quang
Hà Giang
Lạng Sơn
Thái Nguyên
Yên Bái
Hòa Bình
Láng
Nam Định
Ninh Bình

Phủ Liễn
Đông Hà
Đồng Hới
Hà Tĩnh
Hồi Xuân
Huế
Nam Đông
Thanh Hóa
Tương Dương
Vinh
Ba Tơ
Đà Nẵng
Nha Trang
Phan Giang
Phan Thiết
Quy Nhơn
Trà My
Tuy Hòa
Ayunpa
Buôn Ma
Đắc Nông
Kon Tum
Cà Mau
Cần Thơ
Rạch Giá

20

Fig. 2. Annual sunshine days in some typical stations in climate zones
(Phan Van Tan, 2010)

The records of extreme heat are being broken easily in several places in Vietnam.
In other words, the time span between two recorded heat waves is shortened and the next
extreme heat is higher than that in the previous year. In 2010, in two consecutive months,
June and July 2010, the highest temperature of the heat wave in Northern Delta and North
Central generally fluctuated from 400C to 410C. The highest temperature recorded at Con
Cuong station (Nghe An province) was 42,20C (compared to the previous record was 420C
in 1980). In 2015, during the long-lasting heat wave on May, June and July 2015 in the
same places, the recorded temperature in 2010 at Con Cuong station was broken, and the
new record was 42.70C. The highest temperatures during the heat wave of 2015 were
commonly varied from 400C to 420C, and new records were updated simultaneously.
b. Drought
Drought is one of the most common natural disasters in Viet Nam. Drought and
water shortage have been occurred with greater frequency and intensity (Nguyen Van
Thang et al., 2013). The severe droughts have taken place more often, with high frequency
was mainly from January to April (winter rice crop) and from May to August (summer rice
crop). Droughts in winter mainly occurred in the North, the South and Central Highlands;
droughts in summer mainly occurred in North Central and South Central (Fig. 3).

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Fig. 3. The frequency of seasonal drought (three consecutive months)
in some typical areas (Phan Van Tan, 2010).
At the national level, areas that suffered drought the least were mainly in the North
East and areas suffered the longest span were concentrated in the South Central Coast
(drought might last from January till August and September). In term of fluctuations, the
figures for droughts in the North West were the lowest, while those of North Central and
South Central were the highest. The frequency of occurrence of drought monthly and
seasonally slightly differed. According to the statistics, water shortage in Central provinces
and Central Highlands have been increasingly severe in the dry seasons recently. Some

typical prolonged droughts took place in 2010, the water flow in the rivers and streams
nationally was greatly lower than the average ones in several years; the water shortage was
60% to 90% in some places, water levels in many places in Central Vietnam were the
lowest with the rare occurrence of 40 - 100 years/time. In 2005, the lowest water level in
the record was seen on major rivers over the country. In the North, new records of lowest
water level were updated in some major stations in Lo River, the downstream of Hong
River in Ha Noi, and the downstream of Thai Binh River (Pha Lai). Similarly, the lowest
water level of the data also is observed in the Central and the South, Ma River in Ly Nhan,
DakBla River in KonTum, Cai Nha Trang River in Dong Trang, and Cuu Long River.

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c. Heavy rain
Rainy season starts in April and May and lasts until October and November,
particularly the rainy season in South Central roughly ends in November and December.
On average, there are about 25 showers of heavy rains across the country, the first heavy
rains of the year usually occur in the North and the Central Highlands (in March and
April), and later in other areas in the country. In the coastal zones, heavy rain moves from
the North to the South over time and usually reaches a peak in months of the fall. Different
from the relatively uniformly change patterns of temperature, heat and drought, the
increase and decrease of rain in climatic regions in the past decades have random
properties, lowering the statistical reliability (Nguyen Dang Quang et al. 2013). While
many studies show an increase in the rainfall in the South in the last four or five decades
(Endo et al, 2009; Phan Van Tan et al, 2010; Nguyen Dang Quang et al, 2013), the trend in
the North was different. More specifically, some researches show that the rainfall in the
North decreases uniformly (Endo et al, 2009; Phan Van Tan et al, 2010), whereas other
research papers demonstrate an increase in the rainfall in some places at Northern Delta
and North East (Nguyen et al, 2013). Furthermore, the research by Nguyen et al. (2013)
demonstrated a decrease in the rainfall in Highlands, but the decrease is not

proven statistical reliability. The difference between these results can be attributed to using
different approach and the length of statistics, locations and the number of observed
stations. More importantly, a general conclusion is brought about from among research on
the trend of heavy rain in Viet Nam, there is a clear correlation between global warming
reflected by sea surface temperature in the Eastern Pacific Ocean (the areas NINO 3.4)
with changes in climatic conditions in Southern provinces of Vietnam.

Fig. 4. The value of slope a1 of heavy rain data from 1961 to 2007 at typical stations
(Phan Van Tan et al., 2010)
Apart from research on the trend and development of rain, studies on heavy rain
have also been conducted recently. These studies show that extreme phenomena, historical
values together with human and economic losses are likely to increase (IPCC, 2013). The

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observed data confirm that the number, intensity, and location of heavy rains are unusually
high. For example, in the first half of October 2010, there were two torrential rains causing
devastating floods in the history from Nghe An to Quang Binh provinces. The total volume
of the rainfall within 10 days fluctuated from 700mm-to 1600mm, accounting for 50%70%, even 80%-90% the annual precipitation. There were pouring rains in some places
(for example, the rainfall in Tuyen Hoa on October 3rd was 470mm and that in Ba Don on
October 5th was 540mm), and lasted for a long time with the highest intensity during over
past 60 years. Consecutive floods triggered serious inundation in days, several places were
flooded to 4m-6m, causing damage to people, property and traffic and irrigation
constructions. The unusual torrential rains were not only in the rainy season but also took
place in the dry season, particularly, the rain in March 2015 (March 24-27, 2015) in Thua
Thien Hue - Quang Ngai with the average rainfall of 300-450 mm, and records of rainfall
were set in several places. Among recent heavy rains, it is important to study the heavy
rains in the North at the end of July and beginning of August 2015. The records of intensity
were in narrowed areas, mainly occurred in some communes of Quang Ninh province.

Heavy rains mainly took place in Cua Ong, Ha Long, Co To (Quang Ninh), while nearby
locations were Hon Dau and Bach Long Vi (Hai Phong), the intensity of heavy rains was
lower. The precipitation of Quang Ninh province generally fluctuated from 1000-1300mm,
especially the figure for Cua Ong was approximately 1600mm; Bai Chay station registered
the highest precipitation in 1960‘s data at 387mmm (28/7/2015). The probability of this
rare occurrence is estimated to be approximately 500 years.
d. Typhoons and tropical depressions
Meteorological extremes such as typhoons, tropical low pressure, cold spell, and
winter freeze have also recorded new historical points. Firstly, unusual developments of
typhoons and tropical low pressure should be taken into consideration - these phenomena
are regarded as deadliest natural disasters in Vietnam. On March 2012, the No.1 typhoon
(Pakhar typhoon) affected the Northern provinces in Vietnam. In fact, early typhoons that
take place in March are rare (the last time this phenomenon was recorded was 31 years
ago), and Pakhar typhoon was the sole phenomenon that still reached the typhoon level
when it landed in Viet Nam during the past 61 years. In the same time, the No.8 typhoon
(Son Tinh typhoon) did not follow climatic patterns when it landed in Thai Binh and Hai
Phong provinces in last October with magnitude of 11-12 and the highest ones varied from
14-15. After that, the typhoon changed direction, moving in the Northeast along the coast
of Hai Phong-Quang Ninh and eventually weakened into a low-pressure zone. This
typhoon has caused strong winds and heavy rains in the Eastern provinces of North and
North Central, seriously damaging people and properties. Hurricanes with magnitude of
14-15 seem to appear more in the South China Sea, such as typhoon No.6 (Megi typhoon
in 2010 and Haiyan typhoon in 2013,…). 2017 was affirmed as the year with the greatest
number of typhoons and tropical depressions in the past 50 years in the East Sea, including
20 typhoons and tropical depressions. These figures outnumbered that in 2013, in which

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there were five typhoons and two tropical depressions landed in Viet Nam. On the sea, the

huge waves recorded occurred during the North East monsoon and typhoons. On November,
2013 Haiyan typhoon caused waves which were 10 meters higher in the area between the
South China Sea and the Central Coast of Viet Nam. The recorded wave was 4.5 meter at
Bach Long Vi Island which occurred in the North East monsoon in January 2016.
4. Social and economic impacts of extreme weather in Vietnam
In Vietnam, the vulnerability of the natural and social system depends very much
on the degree of danger of extreme weather, density, adaptability of exposed entities and
some natural factors such as geology, geomorphology, terrain, hydrology, etc.
In general, since 1989 the number of deaths (social harm) and total economic loss
(economic damage) due to natural disasters in Vietnam is complex, but overall there is a
tendency to increase along with GDP growth. Over the last 30 years, natural disasters have
killed and lost about 500 people, injured thousands, lost about 1.5% of GDP annually (Tran
Tho Dat and Vu Thi Hoai Thu, 2012). Only in five years from 2002-2006, natural disasters
caused about 1,700 people died, property damage estimated at VND 75,000 billion. The total
value of losses caused by natural disasters in 2013 is estimated at nearly VND 30,000 billion
(twice more than that in 2012), 313 deaths and 1150 injuries (GSO, 2013).

Fig. 5. Economic losses and death caused by disaster 1999-2013
(SREX report Vietnam, 2015)
Regarding damage by disaster types, Vietnam suffered most from tropical cyclones,
floods, followed by droughts and landslides. During 13 years (1990-2012), tropical cyclones
caused losses of nearly $ 4.7 billion, floods costing nearly $ 3.7 billion while droughts and
landslides caused losses of 649 and 2.3 $ millions, respectively. The indirect damage of floods
is partly attributable to heavy rainfall during and after storms, as rainfall in storms can account
for up to 25% of total annual precipitation in some coastal stations of Central Vietnam.

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Fig. 6. Economic losses caused by types of disasters in Vietnam

(EM-DAT The international disaster databases, 2015)
Climate extremes cause different losses to sectors of the socio-economic system.
The impact of climate change (expressed as a percentage of GDP from high to low) for
each sector (for 2010/2030) is as follows: Labor productivity is 4.4%/8,6%; aquatic
products: 0.5% /1.6%; agriculture: 0.2%/0.4%; biodiversity: 0.1%/0.1%; The extreme
weather (in 2010/2030) includes sea level rise of 1.5%/2.7%, hot and cold weather of
0.1%/0.3%; floods and landslides of 0.1%/0.1% (DARA, 2012).

Fig.7. Loss (million VND) of some main sectors due to disasters form 1989-2009
(SREX Report Vietnam, 2015)
Total losses due to natural disasters are highest for industries that are heavily
dependent on weather, climate, and terrain, land, such as agriculture, fisheries, irrigation
and transportation. If the sea level rises by 1 m without coping activities, most of the
Mekong Delta will be submerged for long periods of time, and property damage is
estimated at $ 17 billion.

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By the end of the 21st century, if the sea level rises by 1 m, 6.3% of Vietnam's area,
about 39% of the Mekong Delta, over 10% of the Red River Delta and Quang Ninh, over
2.5% of the area Central and over 20% of Ho Chi Minh City area are at risk of flooding
(MONRE, 2012).The area of agricultural land and aquaculture is most inundated (10,962
km2) when sea level rises by 76%, respectively, followed by wetland with 1,895 km2 and
13%, forest and natural vegetation with 1,159 km2 and 8%, and residential areas with 302
km2 and 2%. Coastal industrial zones of the Mekong River Delta, the Red River. Delta and
the North Central Coast are the most vulnerable due to sea level rise of 1 m (The sea level
rise of 1 m directly affects 16% of the population of the country, nearly 55% of the
population in the Mekong Delta provinces; over 9% of population in Red River Delta and
Quang Ninh; near the 9% of the population in the central coastal provinces and about 7%

of the population in Ho Chi Minh City. At the same time, over 4% of the railway system,
over 9% of national highways and about 12% of Vietnam's provincial roads will be
affected. The highest level of sea level rise is in the Mekong Delta and the Red River
Delta. According to UNDP (2012), among the developing countries, Vietnam is one of the
countries most vulnerable to sea level rise.
The impact of sea level rise on 84 coastal developing countries by the six indicators
of land use, population, GDP, urban size, agricultural land size, and swampy area shows
that Vietnam is one of the five countries most affected by the 1m high sea level rise
(Dasgupta et al., 2009). Moreover, the World Bank ranked Vietnam as one of 12 World
Bank borrowers most affected by sea level rise due to climate change.
The impact of radicals on the community is also reflected in the decline in
livelihoods. Nearly half a million Vietnamese have a primary income from fishing and
other two million people with incomes associated with fishery. The livelihoods of these
people depend on climatic factors and natural resources, so life is particularly uncertain
and at risk from natural disasters as well as weather patterns. Provinces in the Mekong
Delta and Central Coast are economically vulnerable as the majority of their income is
related to fishing.
However, if adaptating appropriately to extreme climate, Vietnam can reduce the
negative impact of hazards and vulnerabilities. Flooding in the Mekong Delta is a
phenomenon that occurs annually, bringing many benefits to people in the region such as
supplying fishery resources, sedimentation for the Delta, increasing agricultural production
for the production season, wash away the toxic substances accumulated in the lowlands
and reduce the vulnerability caused by flooding here. Residents adjust to living with
floods, production activities and activities change in the direction of adaptation, taking
advantage of opportunities caused by floods, thereby reducing exposure to hazards,
vulnerability to flooding.
5. Conclusion and recommendations
Climate change is occurring and having broad impacts across the world. Climate
change projections draw a grim picture of Vietnam‘s climate vulnerability in the coming
decades. A transformation of different sectors-including agriculture, water resource


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management, energy, fisheries, forestry, and infrastructure is needed to counter climate threats
and enhance Vietnam‘s adaptive capacity. To improve disaster preparedness and build longerterm resilience, Vietnam should act now to adapt to changing climate. As in many countries,
Vietnam‘s risk and vulnerability are intensified by unplanned urban development,
inappropriate land use, and ecosystem degradation. Yet it is still possible for the country to
correct course if its policy makers and communities take right and appropriate actions.
A holistic and integrated approach that includes both structural and nonstructural
measures is proposed to address impacts of extreme weather and to promote longer-term
resilience measures across key sectors. Tackling the impacts of all types of disaster risks
nationally will require well thought-out strategic planning and coordinated implementation
of medium- and long-term measures from a multi-hazard perspective. Such planning must
be backed by sound local knowledge, scientific understanding (for targeting and
prioritizing investments for technology development and adoption), infrastructure creation,
and capacity building. To effectively address the extreme weather, an integrated approach
using both structural and nonstructural interventions (policies, capacity building,
information, technologies, infrastructure, and services) is needed.
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