Geographia Technica, Vol 17, Issue 2, 2022, pp. 14-25


Fitriana Nur Indah SARI , Denny Nugroho SUGIANTO , Kunarso KUNARSO

DOI: 10.21163/GT_2022.172.02

ABSTRACT: Semarang is the capital city of Central Java located in the Northern Coastal Area of Java which floods have occurred quite often. Apart from the natural causes, the rapid development in the area resulted in worsened land subsidence leading to exacerbation of the flood’s occurrence. During the last 10 years, there have been at least 15 flood events occurred in the area that was recorded by National Disaster Management Authority but early warning about these incidents is not given much. By using event data from the last 10 years, floods will then be analyzed to determine the characteristics based on three parameters, which are meteorological parameters (rainfall and wind), oceanographic (tidal wave and waves), and land subsidence in the area to create a threshold for early warning system based on these parameters. The results show that each parameter has significant influence on the occurrence of coastal flooding. Ten occurrences of coastal flood in Semarang happened on rainy season and the others on dry season. In rainy season, tidal height for each occurrence varied from 16.58 – 47.12 cm from Mean Sea Level (MSL) accompanied by heavy-extreme rainfall during or the previous day of the flooding. Rain that occurs at higher plains also affects the incidence of flooding in the coastal area of Semarang. While in dry season, tidal waves have greater influence with 80% of the occurrences have high tides above 45 cm from MSL. Wind direction and mean wave direction comes from Northwest for 46.67% and 80% of the cases. These results can be used as the preliminary threshold to increase level of alert before issuing an early warning. The average of rate of displacement for land subsidence in Semarang City is 8.9 cm/year in 2020, which indicates that if this condition occurs continuously, the potential for coastal flooding will increase regardless of season and tidal height happen in the Semarang area.

Keywords: Coastal flood, Meteorology, Oceanography, Land subsidence, Early warning system.

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