Understanding rainfall characteristics during Jakarta’s flood using global satellite mapping of precipitation data (Case study: Flood in Jakarta, January 1st 2020)

Abstract

The majority of flood cases in Jakarta are caused by exceeding water in Ciliwung River Basin, the most high-risk basin for flooding in Indonesia. Rainfall characteristics of each flood phenomenon are distinct, as well as the rainfall scheme during the flood in Jakarta on January 1st, 2020. The aim of this research is to understand the characteristics of rainfall triggering floods in Jakarta and its surroundings on January 1st, 2020. A comparison analysis between those characteristics with climatology condition and extreme threshold of precipitation is performed. The composite of hourly-rainfall data from Global Satellite Mapping of Precipitation was analyzed to understand the climatology/general characteristic of rainfall in Ciliwung’s upstream, midstream, and downstream. Moreover, analysis of rainfall was performed using observational-rainfall data from weather stations (during the event) and hourly rainfall data from satellite (GSMaP) (for calculating rainfall during the event and the extreme threshold within 2001-2020). The composite analysis results in a diurnal pattern of rainfall shown in the upstream during December-January-February (DJF) and a semidiurnal pattern of rainfall in the midstream and downstream especially during January and February. During the flood on January 1st, 2020, there is a semidiurnal pattern along the watershed with the first peak of rainfall intensity reaching 30 mm/hour at 16.00–18.00 Local Time (LT) and the second peak from night until early morning with lower rainfall intensity. The first peak of rainfall intensity is exceeding the extreme precipitation threshold in the midstream and downstream. The Hovmoller diagrams reveal a propagation of rainfall from upstream to downstream from December 31, 2019, in the afternoon to January 1st, 2020, in the morning. Generally, a semidiurnal rain propagating from upstream to downstream with intensity exceeding the extreme precipitation threshold is objected to be the leading cause of flood in Jakarta and surrounding on January 1st, 2020. The results can be used to increase the awareness of rainfall patterns in Ciliwung River Basin as one of the mitigation measures for flooding in Jakarta and its surroundings.