Hydro-Meteorological Aspects of the 2021 South Kalimantan Flood: Topography, Tides, and Precipitation
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This manuscript has been submitted for publication to the INTERNATIONAL JOURNAL OF REMOTE SENSING AND EARTH SCIENCES. Please be advised that future manuscripts may have different content. If accepted, the final version of this manuscript will be updated in the ‘Peer-reviewed Publication DOI’ link. For feedbacks and comments, please feel free to contact any of the authors. Hydro-Meteorological Aspects of the 2021 South Kalimantan Flood: Topography, Tides, and Precipitation Munawir B. Pratama1, Rafida M. Withono2, Ismail N. Azkiarizqi2 1Ocean Engineering Department, Institut Teknologi Bandung 2Water Resources Engineering and Management Department, Institut Teknologi Bandung e-mail: [email protected] Abstract. The 2021 South Kalimantan Flood is said to be the greatest flood ever take place in the province. This study aims to provide an overview of the disaster and assisting future research. Hydro-meteorological conditions such as topography, tides, and precipitation are described. Between January 10 – 19, extreme rain events occurred in South Kalimantan, a province dominated by low lying land with elevation < 7 m. The total precipitation during those 10 days reached 672.8 mm, resulting in a massive water accumulation at downstream. The peak was on January 14, the precipitation in Banjarbaru recorded a 250 mm/day, a 25-year return period value. Furthermore, the spring tide occurred at the same time, slowing the flushing in the tidal river, Barito River. Assessment of ERA5, TRMM, and GPM prediction data indicated that the latter is the most suitable to study the extreme rain events in South Kalimantan. Using the 20-year of GPM data, it is found that ENSO and IOD coexist with both the highest and lowest anomalies. With La Nina at the end of 2020, a positive precipitation anomaly in 2021 should be expected. This extreme precipitation is suspected as the main driver of the 2021 South Kalimantan Flood, and the impact gets amplified by the spring tides. Nevertheless, the significance of other factors, such as the land-use change is crucial to be studied. Keywords: Natural Disaster, Hydrological Hazard, Meteorological Hazard, Indonesia, Extreme Events, Precipitation Anomaly. Submitted to: International Journal of Remote Sensing and Earth Sciences 1 INTRODUCTION Natural disasters are categorized into 6 groups, geophysical, hydrological, meteorological, climatological, biological, and extraterrestrial (IRDR 2014). Since the early of 2020, the biological hazard, namely Covid-19, had hit and kept the Indonesian government and various countries busy across the globe. In addition to that, geophysical, hydrological, and meteorological disasters had occurred in various regions and in a short period in early 2021. In South Kalimantan Province, extreme rainfall lasted for days resulting in flooding. Floods in South Kalimantan were not the first time. In 1928, there were documentations regarding flooding in Barabai, Hulu Sungai Selatan Regency (KITLV 83630 1928). The Central Bureau of Statistics (Badan Pusat Statisik - BPS) of South Kalimantan recorded 286 flood events Figure 1 Overview of South Kalimantan from 2012 to 2019. Banjarmasin was the Province. Area of interest is cities 1 – 11. least affected location, with only 1 Table 1 List of cities, main districts, and its incident, meanwhile, Balangan Regency elevation (BPS Kalimantan Selatan 2021). had 78 flood histories (BPS Kalimantan Selatan 2021). Even so, the floods that Main Elevationsa No Cities hit South Kalimantan in January 2021 Districts (m) were said to be more intense than previous events. As of January 14, BNPB 1 Banjarmasin - 5 reported that 24,379 houses were 2 Banjarbaru - 27 inundated and 39,549 people were 3 Banjar Martapura 13 evacuated (BNPB 2021a). 4 Tanah Laut Pelaihari 64 This study aims to provide an 5 Barito Kuala Marabahan 9 overview of the South Kalimantan Flood 2021, by summarizing reports and 6 Tapin Rantau 8 information from other sources. Natural 7 HSS* Kandangan 11 conditions during the disaster will be 8 HST* Barabai 9 provided, such as topography, tides, and 9 HSU* Amuntai 6 precipitation. It is hoped that the 10 Balangan Paringin 29 information and hypotheses in this paper will provide a basis and may assist 11 Tabalong Tanjung 16 Tanah further studies in this case. 12 Batulicin 2 Bumbu 2 MATERIALS AND METHODOLOGY 13 Kotabaru Kotabaru 32 a Datum in Mean Sea Level (MSL) 2.1 Area of Study * HSS: Hulu Sungai Selatan The study discusses the South * HST: Hulu Sungai Tengah Kalimantan Flood 2021. The domain of * HSU: Hulu Sungai Utara study is shown in Figure 1, including 13 cities with details provided in Table 1. and Banjarbaru which only occupy 1.5% The total population of South of the province's area. Kalimantan in 2019 is 4.24 million According to the literature, 30.16% of people with an area of 38,744.23 km2 land in South Kalimantan is forest and (BPS Kalimantan Selatan 2021). shrubs, and 20.09, 10.98, 2.33 and However, 22.36% of the population is 1.44% respectively are for plantations, concentrated in the cities of Banjarmasin rice fields, settlements, and mining. Submitted to: International Journal of Remote Sensing and Earth Sciences Geographically, the province's average 14. The most severe impacts were felt in height is 17 m with 38.809 hectares used Banjar (Pengaron), Tanah Laut (Bumi for rivers, lakes, reservoirs, and ponds Makmur), Tapin (Binuang), and HST (BPS Kalimantan Selatan 2021). The (Barabai and Hantakan), where water Barito River is the largest river in South rose from about 50 cm to more than 150 Kalimantan and the widest river in cm in just 1 night (BNPB 2021b). Indonesia. Banjarmasin which was not flooded before, was inundated about 30 – 50 cm. 2.2 Flood Records Tanah Laut, which had experienced The schematization of the Barito River flooding since January 10, was suffering system at South Kalimantan Province is a significant increase in flood height due illustrated in Figure 2 (Manalu 2021). to a collapsed retaining wall at the The eleven flooded cities are visualized in Takisung Pond (Balai Hidrologi dan the figure. The general summary of the Lingkungan Keairan 2021). flood events is given in Table 2. These From January 16 – 19, the rain lasted data were compiled from field 3 days with moderate to heavy intensity observation and disaster report provided (BMKG 2021a). The series of extreme by BPBD. Since January 10, there were rain events contributed to increasing the 5 cities affected by the flood. The water discharge of the Barito River to 2.08 levels at the four weirs (upstream side) billion m3, far exceeding its capacity of on January 10 – 13 were at 100, 26, 42, 230 million m3 (Tirto 2021). Table 2 and 25 cm in Banjar (Karang Intan), shows that 11 cities were flooded on Balangan (Pitap), HSS (Amandit), and January 16. Meanwhile, observations at HST (Batang Alai). the weirs showed a gradual decline, After heavy rains on January 14 – 15, namely 69 - 36, 110 - 40, and 22 - 6 cm observations at the weirs surged to 230, for Balangan, HSS, and HST. However, in 202, 150, and 260 cm for each location. Banjar, the water level still fluctuated Consequently, the flood hit 8 cities with between 150 - 170 cm. a considerable inundation on January Figure 2 Schematization of Barito River system at South Kalimantan Province. Submitted to: International Journal of Remote Sensing and Earth Sciences Table 2 General records of the 2021 South Kalimantan Flood, numbers 1-11 represent cities. Dates Times 1 2 3 4 5 6 7 8 9 10 11 07:00 - 20 - - - - - - - - 40 10/01 14:00 - - - - - - - - 30 - 20 - < 50 22:00 - 30 - - - - - - 70 40 07:00 - 40 - - - - - 30 - 11/01 14:00 - - - - - - - 40 22:00 - 20 - - - - - - 20 - 07:00 - - - - - - 40 - 40 12/01 14:00 - 30 50 - - - - - < 30 22:00 - - - - - - 20 - 07:00 - - 40 - - - - 20 50 - 13/01 14:00 - - - - - 70 20 20 - 22:00 - - - - 20 30 50 - 07:00 < 50 - - - 30 - 100 70 - 14/01 200b 14:00 50 - 10 100 – - 100 - 22:00 - 50 – - 200 - 150c 07:00 - 100 - - 50 - 50 15/01 14:00 - 150 30 - - 60 < 20 50 – 22:00 < 100 60 60 07:00 (250) 100 70 - 50 - < 40 30 - 16/01 14:00 100 60 60 10 - 22:00 < 10 60 07:00 50 - 17/01 14:00 30 - < 70 20 - 70 50 30 - 22:00 - < 30 30 60 07:00 - 30 - 40 - < 50 < 40 50 60 18/01 14:00 - < 30 10 < 20 20 - 22:00 - - - 40 < 20 07:00 - - - - 10 - 40 - 20 19/01 14:00 < 40 - < 10 - - - - - 30 50 22:00 - < 70 - - - - 10 - As of January 19, there were still 5 topographic data with a resolution of 8.3 districts inundated as shown in Table 2. x 8.3 m2 for the Indonesian regional area, Based on the visualization of the provided by the Geospatial Information Sentinel-1 satellite on January 20 (see Agency – Badan Informasi Geospatial, Figure 3), large-scale inundation BIG (BIG 2021a). The data is an occurred in the downstream areas of integration of IFSAR, TERRASAR-X, and Barito Kuala, Tanah Laut, and Banjar ALOS PALSAR. Previous studies had (Copernicus Sentinel 2021; Purwonegoro shown that DEMNAS offers better 2021). Flood events were also observed accuracy than SRTM (Nurtyawan and upstream and identified as lower Fiscarina 2020). Elevation discrepancy elevation areas, namely in several areas between DEMNAS and measurement in Barito Kuala to HSU. data is generally influenced by land cover, only a small part is influenced by 2.3 Data Compilation elevation. Topography Tides Topography or digital elevation model The tidal observation station of BIG in (DEM) used DEMNAS data, which are South Kalimantan was less relevant publicly available. DEMNAS is since the location was out of the area of Submitted to: International Journal of Remote Sensing and Earth Sciences the instruments is the precipitation monitoring station, which can be found at a meteorological or climatological station.