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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
Relation, response and change of near-surface air temperature
and rainfall in Thailand
Saisunee Budhakooncharoen1*
1
Assistant Professor, Civil Engineering Department, Mahanakorn University of Technology
51 Cheum Samphan rd., Nong Chok, Bangkok 10530, Thailand
*Corresponding author, e-mail [email protected]
ABSTRACT
54–year ground observations during 1952–2005 were used to analyze the relation, response
and change of over land near-surface air temperature and rainfall in Thailand. Monthly air
temperature and precipitation data were analyzed using 29 synoptic stations spatially
distributed in the whole kingdom of Thailand. Regional temperature and precipitation trend of
change based linear regression and nonparametric, Mann-Kendall test methods were presented.
Rainfall and temperature anomalies relative to the average for 1952 – 2005 were compared. It
was found that the maximum monthly temperature increasing trend was observed in most
areas. Minimum monthly temperature also exhibits both increase and normal tendencies
throughout the country. However, the maximum monthly temperature increase rate is greater
than that of the minimum one. The result of annual volumetric rainfall tracking showed the
positive trend which indicating the increase in annual amount within the northeastern border,
central, eastern and the east coast peninsular of the country. Five decades of annual rainfall
and temperature anomalies relative to the average for 1952 – 2005 graphically illustrated
some opposition, especially in eastern region of the country which is located near to the Gulf
of Thailand.
KEYWORDS
Climate change; long-term climate variation; Mann-Kendall test method; rainfall and
temperature anomalies; temperature and precipitation trend of change
INTRODUCTION
Global warming in the recent decades and its projected continuation is the major concern of
various human sectors. Increasing global temperature might cause sea level to rise and is
expected to increase the intensity of extreme weather events and to change the amount and
pattern of precipitation. One of the remaining scientific uncertainties includes how warming
and related rainfall trend will lead to relation, response and change of each other. The earth’s
near-surface air temperature and rainfall are therefore investigated in this study. To promote
the long-term climate variation research, the regional temperature and precipitation trend of
change based 29 synoptic stations spatially distributed in the whole kingdom of Thailand was
tracked by using linear regression and nonparametric, Mann-Kendall test methods. Rainfall and
temperature anomalies relative to the average for 1952 – 2005 were compared. The major aim
is to seek the relation and response of over land near-surface air temperature variation on
rainfall within the study area.
Saisunee Budhakooncharoen
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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
METHODOLOGY
The major issue to address in this paper is to observe the relation, response and tendency of
change of over land near-surface air temperature and rainfall within the monsoon Asia. To
cover this issue closer, attention must focus on two broad areas: data collection and
methodology or technique development.
For data collection, the temperature and rainfall monitoring systems in Thailand are well
resourced, designed and coordinated. This allows concrete conclusions for detection of the
past change and variability within the region. All of the data used in this research were
extracted from the official database of Thai Meteorological Department (TMD) and Royal
Irrigation Department (RID). In correspondence with the task, the following demands to
hydro-meteorological information take place:
• Time series of information have to be with a period as long as possible for a determination
of long-term tendency,
• Time series should have to include as less as possible of missing data for correct and
effective determination of long-term tendencies and their parameters.
For technique development, very little research effort is currently placed on hydrometeorological aspects of change. Since the basic science goal of this research is to promote
the better understanding and quantify the hydro-meteorological relation, response and change
at various temporal and spatial scales, visual evidence of observed hydro-meteorological
tendency will be investigated using the appropriate time series analysis approach. Then, a
statistical test modeling work will be applied to identify its trends for all historical records.
The long term trend of the hydro-meteorological time series including near-surface air
temperature and rainfall observations will be detected by using two trend detection methods.
They are namely linear regression and nonparametric Mann – Kendall method (Mann, 1945
and Kendall, 1975).
The methodology is as follows:
1) Data collection: Monthly air temperature and rainfall time series for the period 54 years
during 1952 to 2005 from 29 synoptic stations spatially distributed in the whole
kingdom of Thailand were collected. These data were obtained from the Thai
Meteorological Department (TMD) and the Royal Irrigation Department (RID),
2) Tracking trends of hydro-meteorological change using regression based and Mann – Kendal
methods subject to the key indicators namely maximum and minimum monthly air
temperatures and annual rainfall,
3) Determine the rainfall and near-surface air temperature anomalies relative to the
average for 1952 – 2005.
THEORY
Two trend detection methods were employed in this study. They are namely linear regression
and nonparametric Mann – Kendall methods.
Linear regression fits a regression line to the series. Actually, the slope of regression describes
whether the trend is positive or negative. It requires the assumption of normal distribution.
The null hypothesis is that the slope of the line is zero. The linear regression is directly
applied to the time series rather than to the rank. This method is therefore very good for visual
detection of the trend.
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Relation, response and change of near-surface temperature and rainfall in Thailand
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
For Mann – Kendall method, let time series x i is ranked from i = 1, 2, …, n-1 and xj from i+1,
i+2, …, n. Each data point xi is used as a reference point and is compared with all other data
points xj such that
sgn(xi – xj) = 1 if xi > x j
= 0 if xi = x j
= -1 if xi < xj
The Kendall’s statistic S is
n −1 n
S = ∑ ∑ sgn( x i − x j )
i =1 j= i +1
If the data set is identically, independently distributed, the mean of S is zero and the variance
of S is
var(S) =
1
[n(n-1)(2n+5)- Σt(t-1)(2t+5)]
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where n is the length of data set and
t is the extent of any given tie or the number of data value in a group of determination.
Then the test statistic is given as follows,
Z=
S −1
var(S)
=0
=
,S>0
,S=0
S +1
var(S)
,S<0
The presence of a statistically significantly trend is evaluated using the Z value. A positive
(negative) value of Z indicates an upward (downward) trend. The statistic Z has a normal
distribution. To test for either upward or downward trend at α level of significance, H0 is
rejected if the absolute value of Z is greater than Z1- α/2 (Rejected H0 : ‫׀‬Z‫ > ׀‬Z1- α/2) where
Z1- α/2 is the standard normal deviates and α is the significant level for the test.
STATE OF STUDY AREA
Thailand covers an area of 513,115 sq.km. The country is bordered by Malaysia in the south,
the Union of Myanmar in the west and northwest, the Loa People’s Democratic republic to
the northeast, and Cambodia to the southeast. As reported in 2005, the estimated population
was about 64 million with a growth rate of 0.32 percent.
The country can be divided into five main geographical regions. They are namely the north,
the central plains, the northeast, the east and the south. The northern region is mainly
mountainous. It is the origin of four major rivers (Ping, Wang, Yom, and Nan) which
converge to become the Chao Phraya River in the central plains. The northeast region
occupies one-third of the country. The area is a high plateau at 100 to 200 m elevations. The
eastern Thailand is bound by the Gulf of Thailand in the south and Cambodia in the east The
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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
southern region of the country is located on the peninsula between the Andaman Sea of the
Indian Ocean in the west and the South China Sea of the Pacific Ocean in the east.
Based on geographical characteristics, Thailand can be subdivided into 25 major river basins
as shown in Figure 1. The average annual temperature varies in the range 23.3 to 28.4 degree
celcius. Average annual rainfall for the whole country is about 1,425 mm. Total annual
rainfall of all river basins is about 800,000 million m³ of which 75 % of this is lost through
evaporation and evapotranspiration. The remaining 25 % (200,000 million m³) is stored in
streams, rivers, and reservoirs.
Figure 1. 25 major river basins in the Kingdom of Thailand
RESULTS AND DISCUSSION
Herein, near-surface air temperature and rainfall time series were employed to detect the
relation, response and trend of change using linear regression and Mann – Kendall methods.
In this investigation, 29 gauge stations were selected on the basis of their geographical
representative throughout the whole country. To maintain reliable and long-term records, time
series observed during 1952 to 2005 were used. It provides a valuable insight into the
following results:
a) Trend of change in distribution of maximum monthly temperature: Figure 2 is the spatial
distribution of the analyses. It was found that the maximum monthly temperature
increasing trend was observed in most areas. Only the inland area within the upper part of
the country, insignificant decrease tendency of maximum monthly temperature is
detected.
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Relation, response and change of near-surface temperature and rainfall in Thailand
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
b) Trend of change in distribution of minimum monthly temperature: Increasing trend of
minimum monthly over land near – surface air temperature exhibited throughout the
country as shown in Figure 3. Mapping trend statistics also shows some no significant trends in
northeastern and southern region of the country. However, the maximum monthly temperature
increase rate is greater than that of the minimum one.
c) Regional annual rainfall trend of change: The results of annual volumetric water
resources tracking shows the positive trend which indicating the increase in annual rainfall
in the northeastern border, western, eastern and the east coast peninsular of the country as
shown in Figure 4. Only at the northern inland area of the country, decrease tendency of
annual rain observation is noticed.
d) Maximum number of consecutive no rain day in a year: The maximum number of
consecutive no rain day in a year within the study area exhibited the slight decrease
tendency throughout the study area as evidenced in Figure 5.
Figure 2. Trend of change in distribution Figure 3. Trend of change in distribution
of maximum monthly temperature
of minimum monthly temperature
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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
Figure 4. Regional annual rainfall trend of
Change
Figure 5. Tendency change of maximum
number of consecutive no rain day in a
year
e) Near-surface air temperature and rainfall anomalies: As shown in Figures 6 – 10, five
decades of annual rainfall and temperature anomalies relative to the average for 1952 –
2005 were graphically illustrated. It shows some opposition, especially in eastern region
of the country which is located near to the Gulf of Thailand. During mid 1950s to 1960s,
rainfall anomaly was approximately 500 mm above the annual average. But near-surface
air temperature anomaly during the same time period was 0.5 – 1.5 oC below average
across the part of eastern Thailand. Since 1980s, the decreasing trend of rainfall in eastern
region of the country indicates the rainfall anomaly below the average annual magnitude.
During the same time span, the positive near-surface heat content anomaly between 0.25 –
1.5 oC expanded in the region. It is doubtful whether the Gulf of Thailand might be the
important source of heat and moisture for the near land area. Nevertheless, it is difficult to
distinguish the relative role of sea – land – atmosphere interactions. Further attempt
requires adequate measurement of the physical properties or parameters to describe the
interaction system.
The anomalies so far for the other regions also show similar opposition. When the over
land near-surface air temperature is above the 1952 - 2005 average, significantly below
average rainfall is obvious.
However, due to the annual anomalies of both hydro-meteorological time series were used
for comparison. It is therefore revealed the response of cold anomaly consistently with the
positive rainfall anomaly. The relative cause of rainfall anomaly in response to over land
near-surface air temperature or vice versa is indistinguishable. If the continuous daily
meteorological time series are taken into consideration, the lag correlation of both data
types might help conclude the way of their interactions.
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Relation, response and change of near-surface temperature and rainfall in Thailand
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
rainfall anomaly
1000
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
500
0
-500
-1000
-1500
1950
1960
1970
1980
Rainfallanomaly, mm
1990
temperature anomaly
East
2000
Near-surfacetemperatureanomaly, celcius
Figure 6. Annual rainfall & temperature anomalies relative to the average for 1952 –
2005 in Eastern Thailand
400
2
1
1
0
-1
-1
-2
200
0
-200
-400
1950
1960
1970
1980
1990
Temperature anomaly
Rainfall anomaly
North
2000
Rainfallanomaly,mm
Near-surfacetemperatureanomaly,Celcius
Figure 7. Annual rainfall & temperature anomalies relative to the average for 1952 –
2005 in Northern Thailand
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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
rainfall anomaly
400
1.0
200
0.5
0
0.0
-200
-0.5
-400
-1.0
1950
1960
1970
1980
1990
temperature anomaly
Northeastern
2000
Rainfallanomaly,mm
Near-surfacetemperatureanomaly, celcius
Figure 8. Annual rainfall & temperature anomalies relative to the average for 1952 –
2005 in Northeastern Thailand
400
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
200
0
-200
-400
1950
1960
1970
1980
1990
temperature anomaly
rainfall anomaly
Central
2000
Rainfallanomaly, mm
Near-surfacetemperatureanomaly, celcius
Figure 9. Annual rainfall & temperature anomalies relative to the average for 1952 –
2005 in Central Thailand
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Relation, response and change of near-surface temperature and rainfall in Thailand
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
1000
1.5
1.0
0.5
0.0
-0.5
-1.0
500
0
-500
-1000
1950
1960
1970
1980
1990
temperature anomaly
rainfall anomaly
South
2000
Rainfallanomaly, mm
Near-surfacetemperatureanomaly, celcius
Figure 10. Annual rainfall & temperature anomalies relative to the average for 1952 –
2005 in Southern Thailand
CONCLUSIONS
The linear regression and nonparametric, Mann-Kendall test methods were established to
analyze the relation, response and change of over land near-surface air temperature and
rainfall in Thailand. The results show that influenced by the effect of climate variation,
temperature has increase trend. Increase tendency of rainfall amount is also noticeable in most
places. Only at the northern inland area of the country, incline trend of annual rain is
observed. The maximum number of consecutive no rain day in a year exhibited the slight
decrease tendency throughout the country. The annual rainfall and over land near – surface
temperature anomalies so far show some opposition. When the over land near-surface air
temperature is above the 1952 - 2005 average, significantly below average rainfall is obvious.
It is still doubtful whether the Gulf of Thailand might be the important source of heat and
moisture for the near land area. Nevertheless, it is difficult to distinguish the relative role of
sea – land – atmosphere interactions. Further attempt requires adequate measurement of the
physical properties or parameters to describe the interaction system. It can be therefore
concluded that earth observation is playing an important role for improving better
understanding on the complex feedbacks involved sea – land – atmosphere interactions.
However, the results in this research clarified the role of climate variation and also provided a
sound basis for recent climate change attribution to the observed trends. In addition, the initial
success of this study is expected to promote further research in the detail of long-term
variation, relation, response and interaction of each other.
ACKNOWLEDGEMENT
The relevant data used in this study were kindly distributed from the Thai Meteorological
Department (TMD) and the Royal Irrigation Department (RID). And the author is grateful to
reviewers whose comments greatly improved the manuscript.
REFERENCES
Kendall, M.G.: 1975. Rank Correlation Methods, Charles Griffin, London. 202 p.
Mann, H.B.: 1945. Nonparametric test against trend’, Econometrica 13, 245-259.
Saisunee Budhakooncharoen
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