Study on Characteristics of Residual Water Level in Jakarta, Semarang, and Surabaya Waters – Indonesia and Its Relation to Storm Events in November 2007

International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 05 19

Nining Sari Ningsih, Wisaksono Suryo, and Suci Dewi Anugrah

 Abstract— Residual water level (non astronomic tide) obtained combination of the astronomical tides (the daily changes in by removing astronomic tides from the observed tidal data and its water level due to gravitational interactions between the earth, relation to storm events have been studied in Jakarta, Semarang, moon, and sun), the storm surges (the transient changes due to and Surabaya waters, which are located along northern coasts of the effects of a storm), and long-term changes (sea level rise, Java – Indonesia. The residual time series was analyzed with the seasonal and decadal changes). The storm tide can cause occurrence of storms in the Western Pacific Ocean, namely Cyclones Peipah, Hagibis, and Mitag in November 2007. severe flooding in coastal regions, especially in low-lying It was found that the highest surge occurred after the Cyclone areas, frequently causing losses of lives and substantial Peipah event on November 9, 2007. It was of about 38 cm in the economic damages. The degree of flooding depends on storm Jakarta waters, 20 cm in the Semarang waters, and 21 cm in the intensity, fluctuations in astronomically generated tides, and Surabaya waters. In general, although the storm surge heights on the slope of the continental shelf. Flooding is worst when November 9, 2007 were maximum, the total sea level still fell surges coincide with high tides. Since coastal zones are at risk below the mean sea level (MSL) in the Jakarta and Surabaya of storm tides, it is necessary to study crucial coastal zones waters, while it only rose to 5 cm above MSL in the Semarang affected by storm tide flooding, especially along northern waters because the surges were associated with the ebb condition coasts of Java. of the astronomic tide. Therefore, the impact of storm surge Storm surge results from the interaction between height induced by the Cyclone Peipah was not significant. atmospheric pressure depression and wind shear stress on the On the other hand, although the storm surge height ( 10 cm) of the Cyclones Hagibis and Mitag on November 25, 2007 was not water surface. The advancing surge combines with the as high as that of the Cyclone Peipah ( 38 cm), in the Jakarta astronomical tide to create a storm tide. In general, Indonesian waters the total sea level rose up to 75 cm above the MSL region is not a passage of tropical cyclone (storms), however, coincided with the spring flood condition of the astronomic tide as Indonesia will still experience indirect impact of the cyclone, well as perigee position of the moon. The total impact of the such as strong wind, high waves (storm surge), and heavy rain Cyclones Hagibis and Mitag was significant causing flooding along regions that near to the generation area of storms. along the northern land of Jakarta. Meanwhile, in the Surabaya Waters, the storm surge height induced by the Cyclones Hagibis The northern coasts of Java closed to the South China Sea and Mitag was of about 17 cm and had a significant contribution and the tropical region of the northwest Pacific Ocean, which to the increasing of total sea level of about 35 cm above the MSL. are the path of the tropical cyclone during summer. Generally, there are 3 to 4 cyclones generated in the South China Sea and Index Term— astronomic tide, residual water level, storms, the tropical region of the northwest Pacific Ocean in averaged storm surges, storm tide. through the years. The trend of Tropical Cyclone number has been increasing in recent years due to global warming [8]. I. INTRODUCTION The storm tide has caused serious disasters along the JAKARTA, Semarang, and Surabaya coastal areas located at northern coasts of Java (e.g., the Jakarta and Semarang coastal the northern part of Java, Indonesia (as shown in Fig. 1) have areas), such as: houses and infrastructures around the coastal often been hit and inundated by severe storm tide, which is a areas being totally flooded, hundreds of families being displaced, tourism activities being unavailable, and damage of Nining Sari Ningsih is with the Research Group of Oceanography, Faculty fishing ships. Moreover, it is often disturbing access to the of Earth Sciences and Technology, ITB, Indonesia (e-mail: Soekarno-Hatta International Air Port of Jakarta. Therefore, [email protected]). Wisaksono Suryo was with the Study Program of Oceanography, Faculty study on storm tide characteristics along the northern coasts of of Earth Sciences and Technology, ITB, Indonesia (e-mail: Java is necessary, primarily from the view of flood defense. In [email protected]). this study, based on available observed tidal data, we have Suci Dewi Anugrah is with the Meteorological, Climatological, and Geophysical Agency of Indonesia (e-mail: [email protected]). investigated the storm tide characteristics at some locations of

116205-7474 IJBAS-IJENS © October 2011 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 05 20

the coasts of Java, namely Jakarta, Semarang, and Surabaya in and atmospheric pressure data as well as tropical cyclone data November – December 2007. We are interested to study the (Table II) have been collected. Depression tracks of the tidal observation data in the period of November – December cyclones are not shown in this paper and they can be found at 2007 because there was severe flooding caused by sea water http://weather.unisys.com/hurricane/w_pacific/2007H/index.ht along the northern land of Jakarta, especially in November ml. Due to lack of local wind and atmospheric data, we used 6- 2007, and it was reported extensively in both electronic and hourly wind and atmospheric pressure data from NCEP print media. (National Centers for Environmental Prediction) to calculate As far as we know, storm tide investigation along the sea level changes caused by local wind set up and inverted northern coasts of Java is still limited, especially study on barometer effect by using (1) and (2), respectively. Local wind storm surge characteristics studied by observed tidal data. In set-up is approximately calculated by (Bowden, 1983): our previous study [6], we have investigated wave height, run- up, and inundation of storm tide along the northern coasts of  sx Java, generated by tides and the Cyclones Hagibis and Mitag  Cx  (1) gh in November 2007 by using a two dimensional (2D) hydrodynamic model. The simulated results showed that although the Cyclones Hagibis and Mitag did not generate where  represents changes in sea level over a finite high storm surges along the coasts of Java (surge heights < 20 horizontal distance x; sx is wind stress; 1 < C < 1.5; g is the cm), the coasts were still severely flooded. gravitational acceleration;  is the density of water; and h is It is suggested that a storm in the South China Sea will be the mean depth of water. Meanwhile, changes in sea level  able to generate swell traveling south into the Jakarta Bay, due to a change in atmospheric pressure pa are given by which is located at the northern coast of Java. When that swell (Bowden, 1983): arrives at the Jakarta coast, it may meet a young sea state being 1 generated by a local breeze from northerly directions. Based    p . (2) on a hydrodynamic simulation, Pandoe (2008) at g a http://www.ristek.go.id/index.php?mod=News&conf=v&id=24 29, from Agency for The Assessment and Application of This is known as ”the inverted barometer effect” in which an Technology of Indonesia, reported that local wind speed of increase in atmospheric pressure is accompanied by a decrease about 10.28 m/s will contribute to raise the water level of in sea level or vice versa. about 20 – 30 cm in the Jakarta Bay. In this paper, we studied storm surge characteristics (e.g., TABLE I surge-heights and periods) along the northern coasts of Java, T HE AVAILABILITY OF OBSERVED TIDAL DATA AT LOCATIONS OF JAKARTA, especially in the Jakarta, Semarang, and Surabaya locations S EMARANG, AND SURABAYA IN THE PERIOD OF NOVEMBER – DECEMBER 2007 based on harmonic analysis and wavelet transform methods. Locations Dates Data Methods By using the harmonic analysis method, the surge-heights were Interval investigated based on residual water level obtained by (Minutes) removing the tidal part from the observed tidal data. 1. Jakarta 1 - 30 15 Harmonic Analysis Meanwhile, based on wavelet theory, it is able to understand November & Wavelet the distribution of spectral density and frequency in the time 2007 Transform domain. The application of the wavelet theory to analyze tidal 1 - 2, 7 - 12, 15 Harmonic Analysis data is gradually widely used in recent years, e.g., [2][5]. The and 19 – 31 researchers applied the wavelet transform method, which December 2007 makes the judgment of the tidal data analysis easier. 2. Semarang 1 - 30 15 Harmonic Analysis November & Wavelet 2007 Transform II. DATA AND METHODOLOGY

In this study, we used observed tidal data at 15-minutely 5 - 31 15 Harmonic Analysis intervals, which was obtained from The National Coordination December 2007 & Wavelet Transform Agency for Surveys and Mapping of Indonesia. The observed tidal data are available at the Jakarta, Semarang, and Surabaya 3. Surabaya 1 - 2, 5 - 10, 21 15 Harmonic Analysis locations in the period of November – December 2007. – 30 November 2007 However, there were some missing observations. Detailed information of the available data during that period is shown in 1 – 31 15 Harmonic Analysis

Table I. December 2007 & Wavelet Transform To know meteorologically induced sea level changes, wind

116205-7474 IJBAS-IJENS © October 2011 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 05 21

TABLE II electronic and print media. TROPICAL CYCLONE DATA IN WESTERN PACIFIC OCEAN (SOURCE: UNISYS TABLE III WEATHER) SEA LEVEL HEIGHTS AND IMPACT OF STORM SURGE HEIGHT INDUCED BY Name Date Max Wind Air Category Based TYPHOON - 1 PEIPAH IN THE JAKARTA, SEMARANG, AND SURABAYA Speeds Pressure on Saffir- WATERS (knot) (mb) Simpson Scale Jakarta Semarang Surabaya 1 Typhoon -1 03-09 NOV 75 > 980 1 Waters Waters Waters PEIPAH 2007 1. Spring Tidal 130 90 265 2 Typhoon -2 20-27 NOV 95 965-980 2 Range (cm) MITAG 2007 2. Neap Tidal 45 50 90 3 Typhoon -2 18-27 NOV 85 965-980 2 Range (cm) HAGIBIS 2007 3. The Storm 38 20 21 surge height induced by III. RESULTS AND DATA ANALYSIS Typhoon-1 Meteorologically induced sea level changes can be seen Peipah (cm) most clearly after the tidal effects have been removed. 4. The Total Sea The total sea The total sea Although the Level during level still fell level just rose storm surge Astronomic tide, obtained from harmonic analysis using the Typhoon-1 below the to 5 cm above height on T_TIDE Program [7], was subtracted from the observed sea Peipah MSL in the MSL in November 9, level to product a residual curve. The residual sea level heights associated associated 2007 was with the ebb with the ebb maximum, the or non astronomic tide, usually known as meteorologically condition of condition of total sea level induced sea level changes, such as storm surge heights, local the the still fell below the wind set-up, and inverted barometer effect. astronomic astronomic MSL in tide tide associated with Observed water level, astronomic tide, and residual sea level the ebb condition heights in the Jakarta Waters (marked by 1 in Fig. 1) are of the astronomic shown in Fig. 2 and it can be seen from the figure that highest tide residual sea level exist on November 9, 2007 of about 39 cm. 5. The impact of Not Not Not significant storm surge significant significant To know how large surge heights generated by the Cyclones height induced Peipah, Hagibis, and Mitag might exist in the Jakarta Waters, by Typhoon - 1 sea level changes induced by local wind set up as well as Peipah

inverted barometer effect are calculated, as shown in Fig. 3. It TABLE IV is found that the sea level changes induced by local wind set IMPACT OF STORM SURGE HEIGHT INDUCED BY THE CYCLONES HAGIBIS up and inverted barometer effect are of about < 1 cm. AND MITAG, AND PERIODS OF THE NON ASTRONOMICAL TIDES IN THE JAKARTA, SEMARANG, AND SURABAYA WATERS Therefore, it suggested that the storm surge height induced by Jakarta Semarang Surabaya Typhoon - 1 Peipah is of about 38 cm. Further analysis shows Waters Waters Waters that although the storm surge height on November 9, 2007 was 1. The storm surge 10 8 17 maximum, the total sea level still fell below the mean sea level height induced in associated with the ebb condition of the astronomic tide by the Cyclones Hagibis and (Fig. 4). Therefore, the impact of storm surge height induced Mitag (cm) by Typhoon - 1 Peipah was not significant. 2. The Total Sea The total sea The total sea The total sea Meanwhile, during the Cyclones Hagibis (19 – 27 Nov Level during the level rose up to level rose up to level rose up 2007) and Mitag (20 – 27 Nov 2007), it was obtained that Cyclones 75 cm above 17 cm above the to 35 cm residual sea level height of about 12 cm on 25 November 2007 Hagibis and the MSL in MSL in above the Mitag associated with associated with MSL in which in that time sea level changes induced by local wind the spring flood the neap flood set up and inverted barometer effect being about < 1 cm and < condition of the condition of the 2 cm, respectively. Hence, it is suggested that the storm surge astronomic tide astronomic tide as well as height induced by Cyclones Hagibis and Mitag was of about perigee position 10 cm. Although the storm surge height ( 10 cm) of the of the moon Cyclones Hagibis and Mitag was not as high as that of Cyclone 3. The impact of Significantly Not significant Significantly Peipah ( 38 cm), total sea level rose up to 75 cm above the storm surge causing increasing height induced flooding along the total sea mean sea level in associated with the spring flood condition of by the Cyclones the northern level of about the astronomic tide as well as perigee position of the moon (as Hagibis and land of Jakarta 35 cm above shown in Fig. 5). Impact of the total sea level was significant Mitag the MSL causing flooding along the northern land of Jakarta. The 4. Periods of the 1 - 4 days 0.5 - 4 days 1 - 4 days flooding occurrence was reported extensively in both Non Astronomical Tides

116205-7474 IJBAS-IJENS © October 2011 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 05 22

In addition, based on wavelet transform approach, we found REFERENCES the energy distribution of residual water level in the Jakarta [1] K.F. Bowden, Physical Oceanography of Coastal Waters. Ellis Horwood Ltd., 1983. [2] D. P. Chambers, C. A. Mehlhaff, T. J. Urban, and R. S. Nerem, Waters during the Cyclones Peipah, Hagibis, and Mitag “Analysis of Interannual and Low-Frequency Variability in Global over frequency and time domains. It was found that periods of Mean Sea Level from Altimetry and Tide Gauges,” Physics and the non astronomical tides in the Jakarta Waters are about 1 - 4 Chemistry of the Earth, vol. 27, Issue 32-34, 2002, pp. 1407-1411. [3] C. C. Huang, “On the Supplement of Tidal Data and the Characteristic days (Fig. 6). of the Astronomical Tide Component,” Master Thesis, Department of We have also analyzed residual sea level heights in the Hydraulics & Ocean Engineering, National Cheng Kung University, Semarang and Surabaya Waters and their relation to the Taiwan, 2005. [4] C. B. Lee, C. C. Huang, C. C. Kao, and C. L. Z. Chuang, “Study on the occurrence of storms in the Western Pacific Ocean (the Characteristics of Storm Surge over Taiwan Eastern Waters by Wavelet Cyclones Peipah, Hagibis, and Mitag) as well as in the Jakarta Transform,” in Proceedings of the Eighteenth International Offshore Waters. Summary of the data processing results are shown in and Polar Engineering Conference, Vancouver, BC, Canada, 2008. [5] Y.H. Lim and L.M. Lye, “Wavelet Analysis of Tide-affected Low Tables III and IV. Stream Flows Series,” Journal of Data Science, vol. 2, Number 2, 2004, pp. 149-163. IV. CONCLUSION [6] N.S. Ningsih, S. Hadi, D. F. Saputri, F. Hanifah, and A. P. Rudiawan, Residual water level characteristics in the Jakarta, “Simulation of Susceptible Areas to the Impact of Storm Tide Flooding along Northern Coasts of Java,” in Proceedings of Conference on Semarang, and Surabaya Waters – Indonesia and their relation Industrial and Applied Mathematics (CIAM 2010), Bandung, 6 – 7 July, to storm events (the Cyclones Peipah, Hagibis, and Mitag in 2010. November 2007) have been investigated. It was found that the [7] R. Pawlowicz, B. Beardsley, and S. Lentz, “Classical Tidal Harmonic Analysis Including Error Estimates in MATLAB Using T_TIDE,” maximum surges at the three locations are of about 21 – 38 cm Computers & Geosciences, 28, 2002, pp. 929–937. after the Cyclone Peipah event, and they are of about 8 – 17 [8] P. J. Webster, G. J. Holland, J. A. Curry, and H. R. Change, “Changes cm after the Cyclones Hagibis and Mitag. Based on this study, in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment”, Science, 309, 2005, pp. 1844 - 1846. it was known that although the surge heights in the three locations are generally less than 40 cm, they may significantly contribute to generate flooding along the northern coast of Java, especially at the Jakarta coast, if the surge event coincided with the spring flood condition of the astronomic tide as well as perigee position of the moon as the case of flooding generated by the Cyclones Hagibis and Mitag along the northern land of Jakarta on November 25, 2007 in which total sea level rose up to 75 cm above the MSL. In this study, we used 6-hourly wind and atmospheric pressure data from the NCEP to calculate sea level changes caused by local wind set up and inverted barometer effect. To obtain more accurate calculation of the sea level changes, it is necessary to use local wind and atmospheric data with high resolution both in space and time. Results of this present research can be used to verify and improve our previous modelling of storm tide flooding in the area of study [6]. This kind of study is currently in progress as an extension of this research work. It is hoped that a better understanding of the characteristics of surge heights and astronomic tides at the three locations, which is obtained from this study, could be significantly valuable for designing both proper management plans and investment policies in the coastal water areas, primarily to reduce the risk of flooding caused by storm tide.

ACKNOWLEDGMENT

The in-situ data used in this study are provided by the National Coordination Agency for Surveys and Mapping of Indonesia. We gratefully acknowledge the supports.

116205-7474 IJBAS-IJENS © October 2011 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 05 23

Fig. 1. Locations of Jakarta, Semarang, and Surabaya (marked by 1 – 3, respectively).

Jakarta, 1 Nov – 31 Dec 2007 Jakarta, 1 Nov - 31 Des 2007 250 Original Time series Observation data Tidal prediction from Analysis Spring Tidal Range :  130 cm Astronomic Tides prediction

Original time series minus Prediction Residual Elevationresidue Neap Tidal Range :  45 cm 200

150

100

LevelWater (cm) Residual time series after removal of astronomic tides 50

-50 26 Okt 5 Nov 15 Nov 25 Nov 5 Des 15 Des 25 Des 4 Jan Date/Month

Fig. 2. Observed water level, astronomic tide, and residual sea level heights in the Jakarta Waters (marked by 1 in Fig. 1).

116205-7474 IJBAS-IJENS © October 2011 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 05 24

Residual Elevation

Peipah Hagibis Mitag

 3 m/s 3 m/s

vektor vektor (m/s) SpeedWind 11/04 11/14 11/24 12/04 12/14 12/24 1/03 (m/s) kecepatan Local Wind Set Up

(cm) Elevation

Inverted Barometer Effect

(cm) Elevation Dates

Fig. 3. Residual sea level heights, wind speed, local wind set up, and inverted barometer effect in the Jakarta Waters (marked by 1 in Fig. 1). The colour squares indicate the time periods of the Cyclones Peipah, Hagibis, and Mitag.

Observation Astronomic Tides Residual Elevation

Dates

Fig. 4. Observed water level, astronomic tide, and residual sea level heights in the Jakarta Waters. The dot line indicates the time of the highest residual water level after the Typhoon - 1 Peipah, namely on November 9, 2007.

116205-7474 IJBAS-IJENS © October 2011 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 05 25

Fig. 5. Observed water level, astronomic tide, and residual sea level heights in the Jakarta Waters. Arrows indicate the time of the heights of residual water level on 25 November 2007 in the period of the Cyclones Hagibis and Mitag events, indicated by the black and green squares, respectively.

Fig. 6. The wavelet energy distribution of residual water level in the Jakarta Waters during the Cyclones Peipah, Hagibis, and Mitag.