The Megacity Jakarta has encountered serious floods associated with high intensity but a short-duration rainfall or low intensity with a long-duration rainfall. During the rainy season, on 4 Feb 2021, Jakarta was inundated as rainfall intensity increased. However, little is known about the meteorological factors that might contribute to this heavy rainfall. In this study, we used the 6-min X-Band Doppler radar, one-hour satellite and reanalysis data to understand the spatial distribution of rainfall and explore the background conditions that might influence the enhanced rainfall over Jakarta and Bekasi River. Other than previous studies, we found that over Jakarta, the areas receiving high rainfall are more widespread and further to the northeast ocean with an intensity of above 4.5 mm h-1. High intensity of rainfall starts to develop in the afternoon over the inland areas at around 08-10Z (3.00-5.00 PM). Background condition shows a strong westerly wind speed crossing over Java Island, and this might initiate the development of rainfall over the region.

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An accurate rainfall data has an important role in the Indonesia Fire Danger Rating System (Ina-FDRS) which has been developed by PTPSW – BPPT since 2017. Continuing the previous study, during wet and dry season, an accurate rainfall data becomes one of the important inputs and has big impact on the Ina-FDRS. Unfortunately, surface rainfall data from AWS and ARG have limited availability especially on the spatial resolution data, therefore Ina-FDRS will use HIMAWARI-8 rain rate data as an input. On the other hand, satellite rainfall data also has limitation on the accuracy, HIMAWARI-8 detects top cloud temperature, then by using IMSRA method to calculate rainfall values. This preliminary study aims to validate rain rate from HIMAWARI-8 satellite image data with ground-based rainfall data from AWS/ARG during fire and non-fire period, from 1 – 31 August 2015 and 15 April – 15 May 2018. Afterward, we will use the validated rainfall data as an input for Ina-FDRS.

Koefisien atenuasi merupakan gambaran seberapa besar cahaya datang berkurang atau hilang dibandingkan dengan energi cahaya datang di permukaan. Pengurangan energi cahaya dikarenakan adanya proses absorpsi dan hamburan oleh kolom air dan materi yang terkandung di dalamnya seperti fitoplankton, padatan tersuspensi dan colored dissolved organic matter. Kuantitas cahaya yang mengalami atenuasi setara dengan jumlah cahaya yang diabsorpsi dan dihamburkan. Penelitian ini bertujuan untuk menganalisis hubungan antara koefisien atenuasi dengan kualitas air, serta mengkaji karakteristik optik perairan Kelurahan Pulau Panggang. Pengukuran spektral menggunakan TriOSRamses yang memiliki sensor irradiance dengan panjang gelombang antara 320 nm sampai 950 nm dan rentang kanal 3,3 nm. Perhitungan koefisien atenuasi (Kd) berdasarkan perubahan downwelling irradiance pada dua kedalaman berbeda. Korelasi Pearson digunakan untuk mengetahui hubungan antara Kd dengan kualitas air. Berdasarkan rentang panjang gelombang, Kd dibagi menjadi 4 yaitu Kd PAR, Kd biru, Kd hijau dan Kd merah. Kd biru dan Kd hijau memiliki hubungan paling erat dengan kecerahan sebesar 0,5406 dan 0,3990 serta bersifat negatif, sedangkan Kd PAR dan Kd merah paling erat hubungannya dengan muatan padatan tersuspensi sebesar 0,4015 dan 0,4073 dan bersifat positif. Perairan Kelurahan Pulau Panggang merupakan perairan turbid dengan nilai Kd PAR > 0,115 m-1.