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Variations of sea level in the Gulf of Thailand during 2001-2010.

Introduction

The Gulf of Thailand (GoT) is located in Southeast Asia immediately to the west of the South China Sea (SCS). The Gulf is a semi-enclosed sea that measures approximately 400-km by 800-km, covering an area of about 320,000 square kilometers. Its location in the global map is between 6 [degrees]N to 14 [degrees]N latitude and 99 [degrees]E to 105 [degrees]E longitude surrounded by the Kingdom of Cambodia, Malaysia, the Kingdom of Thailand and the Socialist Republic of Vietnam (Figure 1.1). It is a part of the Sunda Shelf, which is a submerged connection between Southeast Asia, Malaysia, Sumatra, Java, and Borneo, and is relatively shallow. The mean and maximum depths in the central part in the GoT are about 45 m and 80 m, respectively. This makes water exchange slow, and the strong water inflow from the rivers make the Gulf low in salinity and rich in sediments. The living and non-living resources of the Gulf are great value to the people of the four littoral countries. The management of fisheries, oil and gas resource development is in progress in this region.

The sea level rise is one of many problems of the global warming effects. The long term sea level changes in each area are different. Some regions show that sea level rise is greater than the global average sea level rise. Many researchers studied the rise of sea level and its impacts.

Intergovernmental Panel of Climate Change, IPCC (1990) summarized the global mean sea level rise rates in these 100 years and obtained the best estimate value of 1.05 mm/yr. Moreover, IPCC (1990) reported that the most suitable predicted mean sea level rise will be 0.18 m (0.08-0.29 m) at the year 2030 and 0.44 m (0.21-0.71 m) at the year 2070 from 1985 and they will be mainly due to the thermal expansion of oceans, and the increased melting of mountain glaciers and small ice caps.

Yanagi and Akaki (1994) investigated mean sea level variations in the Eastern Asia using observed sea level data of 16 stations from the Permanent Service for Mean Sea Level (PSMSL) during 1950 to 1991. They estimated rates of mean sea level variation by the least-square regression method. The mean sea levels have risen along the eastern coasts of Japan and the Philippines but they have fallen along the western coasts of Japan and the Philippines, the eastern coast of China and the southern coast of Indochina Peninsula. The rates of mean sea level rise along the eastern coasts of Japan and the Philippines of 3.8-5.9 mm/yr are much larger than that of global mean sea level rise of 1.05 mm/yr.

Niemnil and Trisirisatayawong (2006) determined the rate of sea level change in the GoT using annual sea level data from tide gauge stations of Hydrographic Department, Royal Thai Navy and Port Authority of Thailand such as Sattahip, KoLak, KoMattaphon and KoSichang stations. The results showed that sea level of Sattahip, KoMattaphon and KoSichang stations are raising rates of 0.22, 0.51 and 0.81 mm/yr, respectively, while KoLak station is falling rate of 0.52 mm/yr.

Vongvisessomjai (2006) analyzed sea level in the GoT using 56 years of tide gauge records at KoLak and Sattahip. The results showed that sea level is falling slowly corresponding to the results of Gregory (1993) which used U.K. Meteorological Offices Coupled Ocean-Atmosphere General Circulation Model to find the sea level. He reported that sea level falls in the low latitudes and the GoT of 0-0.05 m.

The National Aeronautics and Space Administration, NASA (2010) reported that the trends of long term sea level are rise using the linear regression method. This report exposed historical trends of global mean sea level from tide gauge records and the average sea level from global satellite measurements (Figure 1.2).

Sea level rise is a major effect of climate change and it is likely to affect millions of people. The IPCC (2007) found that the sea level had changed dramatically in the past, and the rate of sea level rise had increased.

In this paper, the trends of sea level in the GoT are calculated using daily data records from tide gauge stations.

Buoy Stations

The sea level records of Buoy stations are provided by the MD and Hydrographic Department of Thailand. Thirteen buoy stations from the MD are Thachin Estuary, Maeklong Estuary, Banlaem, Bangpakong Estuary, Rayong Estuary, LaemNgob, Prasae, Thachalab, Pakpanang Estuary, Pattani Estuary, Bangnara Estuary, Sichol and Langsuan. Three buoy stations from the Hydrographic Department are Huahin, KoLak and KoPrab. Figure 2.1 shows the positions of buoy stations. The simulated SSE at buoy locations is examined to compare with the observations.

Results

All missing data from the tide gauge stations in the GoT in the study period are less than 10% of data records. Table 3.1 shows the percentages of missing data and mean sea level rise rate (mm/yr) from the tide gauge stations for each station in the GoT in the period 2001-2010. The estimated rates of mean sea level variation in these 10 years are obtained by the least square regression method. The daily mean sea level data (cm) and least square regression linear trend are shown in Figure 3.1--3.6. The mean sea levels have raised most of stations except Thachalab, Prasae, Huahin and Pakpanang Estuary stations where the mean sea levels have fallen. The mean sea level is highest rising with a rate about 18 mm/yr at KoLak and Bangnara Estuary, while it is highest falling with a rate of 11.67 mm/yr at Pakpanang Estuary station.

Conclusions

The results indicate that the trends of sea level from tide gauge stations had been increased in the GoT with rising rates of 0.35-17.91 mm/yr, and falling rates of 1.09-11.67 mm/yr. The results at some stations agree with Yanagi and Akaki (1994).

Acknowledgements

We express our sincere thanks to the Department of Mathematics, King Mongkut's University of Technology Thonburi (KMUTT) for the facilities during this research. The buoy data sets were kindly provided by the MD and Hydrographic Department of Thailand.

References

[1] IPCC, 1990, Climate Change, Cambridge University Press, Cambridge.

[2] NASA, 2010, Global Climate Change [online], Available : http://www.climate.nasa.gov/keyIndicators/.

[3] Niemnil, S. and Trisirisatayawong, I., 2006, Sea Level Trend in the Gulf of Thailand Using Tide Gauge Data, Department of Survey Engineering, Faculty of Engineering, Chulalongkorn University, Thailand.

[4] Vongvisessomjai, S., 2006, "Will Sea Level Really Fall in the Gulf of Thailand?",Songklanakarin Journal of Science & Technology, 28(2), pp. 227-248.

[5] Yanagi, T. and Akaki, T., 1994, "Sea Level Variation in the Eastern Asia", Journal of Oceanography, 50, pp. 643-651.

N. Aschariyaphotha (l),*, S. Klanklaew (2), B. Wichianchai (2) and S. Wanchaijiraboon (2)

(1) King Mongkut's University of Technology Thonburi, Ratchaburi Campus, Bangkok 10140, THAILAND.

(2) Department of Mathematics, Faculty of Science, King Mongkut's University of Technology Thonburi, Bangkok 10140, THAILAND.

* Coresponding author: nitima.asc@kmutt.ac.th

Table 3.1: The percentages of missing data and mean sea level
rise rate in mm/yr at each station in the GoT in the
period 2001-2010.

Station name         Missing data    Mean sea level rise
                          (%)            rate (mm/yr)

LaemNgob                 0.60               10.53
Thachalab                1.14               -1.09
Prasae                   0.01               -2.91
Rayong Estuary           0.10               12.06
Bangpakong Estuary       0.07                8.63
Thachin Estuary          5.30                9.71
Maeklong Estuary         1.51               13.72
Banlaem                  0.06                9.13
Huahin                   0.06               -10.36
KoLak                    2.71               17.91
Langsuan                 0.72                4.00
KoPrab                   9.71               12.05
Sichol                   0.02                5.38
Pakpanang Estuary        0.13               -11.67
Pattani Estuary          0.06                0.35
Bangnara Estuary         0.00               17.90
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Author:Aschariyaphotha, N.; Klanklaew, S.; Wichianchai, B.; Wanchaijiraboon, S.
Publication:Advances in Theoretical and Applied Mathematics
Article Type:Report
Geographic Code:9THAI
Date:May 1, 2013
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