The megacity Jakarta, Indonesia, encounters hydrometeorological hazards driven by intense and/or frequent rainfall. The Madden-Julian oscillation (MJO), a large-scale atmospheric disturbance propagating eastward through the tropics every 30-60 days, influences rainfall variability in Jakarta. Existing studies often rely on coarse-resolution data and neglect the distinct roles of stratiform versus convective rain rates, especially in relation to the MJO. This study examines the locally diurnal and seasonal characteristics of stratiform and convective rain rates and their variations with the MJO, using high-resolution C-band Doppler radar data (2009-12). Results show that although convective rain rates peak in December-February (DJF), the intensity calculated over rainy pixels is higher in September-November (SON). The diurnal afternoon peak of total rain rate is primarily attributed to the convective rain rate over mountains (24%) and lowlands, whereas the morning peak of overall rain rate is affected by the stratiform rain rate (11%). There is a higher proportion of stratiform rain rate during the MJO active phase, and this rain rate is not particularly tied to the diurnal cycle. However, in June-August (JJA) and SON, the suppressed MJO phases produce a larger ratio of stratiform to convective rain rates, with a more localized signature. The stratiform rain rate in the suppressed phase is likely associated with anvils from the isolated convection, while in the active phase, it is linked to the large-scale MJO envelope. The high convective rain rate during SON, despite lower overall totals, implies greater potential for flash flooding due to its intensity. Therefore, understanding the seasonal predominance of rain types by MJO phase can improve early warning accuracy for Jakarta.

The Megacity of Jakarta and its surrounding regions have been currently more vulnerable to severe floods due to extreme rainfall. In this study, the contributions of multiple drivers of regional climate phenomena to extreme rainfall seasonally are examined using a single index of 80 percentile of seasonal maximum of daily rainfall during each event and climatology based on the National Oceanic and Atmospheric Administration (NOAA)'s Climate Extreme Index (CEI). The multi-drivers investigated in this study include cold surges (CS), crossequatorial northerly surges (CENS), Madden-Julian Oscillation (MJO), El-Nino Southern Oscillation (ENSO), and Indian Ocean Dipole (IOD). We used daily rainfall datasets of 7 meteorological stations representing varying topography from lowland on the coast to mountain areas during 1985-2021 (37 years). Results show that the climatology of rainfall is significantly associated with CEI during CENS in the wet season Dec-to-Feb (DJF) (r = 0.8). Meanwhile, in the dry season Jun-to-Aug (JJA), the rainfall is more related to CEI during the negative IOD and La Nina (r = 0.9). Over the lowland, the rainfall intensity >= CEI during CENS has a stronger variation in DJF than in any other season. The second peak of CEI is notably found over the transitional area between lowlands and mountains (Dramaga Station) during Mar-to-May (MAM), JJA, and Sep-to-Nov (SON). This implies the important role of the transitional region in changes of extreme rainfall which has not been exposed previously. The large-scale drivers have induced extreme rainfall intensity in DJF for most stations. In MAM, JJA, and SON, the contribution of CEI is the largest in areas over the south near the mountainous regions.

There has been a dramatic increase in flood events over Greater Jakarta since 2019. However, little study has been found regarding physical characteristics of rainfall during flood events. This study investigates the rainfall drop size distribution during the three cases of severe flood events in the Jakarta area on 31 December 2019-1 January 2020 (Case 1), 15-16 July 2022 (Case 2), and 6-12 October 2022 (Case 3). The characteristic of rainfall drop size is analysed and categorised based on stratiform, convective, and mixed convective-stratiform rainfall. This research used the Automatic Weather Station, Laser Precipitation Monitor, and ERA5 reanalysis datasets from December 2019 to October 2022. Overall, results show that raindrops with particle diameters up to 4 mm exist during the three flood cases over the lowland and mountainous regions. The mountainous region has a higher number of larger diameter sizes compared to the lowland. In Cases 1 and 2, the occurrence of stratiform rainfall dominated the lowland areas, while the convective rainfall was also present in the mountain during Case 1. In contrast to Cases 1 and 2, over the lowland during Case 3, mixed stratiform and convective rainfall have a significant proportion. Meanwhile, the stratiform and convective rainfall over the mountainous region occurred equally. The most prominent feature in Case 1, the stratiform rainfall persisted from 14 to 13 LT on the following day, coinciding with the severe flood over the Jakarta region. The anomaly of high moisture convergence and substantial negative vertical velocity over the lowland during Case 1 might generate a long duration stratiform rainfall that likely contributed significantly to floods.

Extreme rainfall has increased in many regions over the Indonesia Maritime Continent (IMC), including the Indonesia’s newly developing capital city of Nusantara (IKN). In the previous research, rain gauge data from five stations of the Agency for Meteorology, Climatology and Geophysics (BMKG) were utilized. The studies showed a slightly increasing trend of rainfall were observed over all stations. Continuing those studies, this paper aims to gain more detailed spatial and temporal rainfall variability by utilizing gridded rainfall data from satellite remote sensing. The historical data over 23-year period of Global Satellite Mapping of Precipitation (GSMaP) and the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) have been used to identify long-term trends, spatial patterns, and the relationship between extreme rainfall and topographical conditions, as well as other meteorological factors. The analysis will involve descriptive statistics, temporal trend, and geospatial mapping. Eventually, we expect that the findings could help to improve the water availability for food security system, such as determining cropping patterns at certain periods which is urgently required in the region.

The Bekasi River Basin is highly vulnerable to severe and recurrent flooding, as evidenced by significant infrastructure and environmental damage during major events. This study investigates the catastrophic floods of 2016, 2020, 2022, and 2025 by implementing the Rainfall-Runoff-Inundation (RRI) model to simulate key hydrological processes. After validation using historical water level data, the model performed effectively, achieving the highest coefficient of determination (R2 = 0.75) and lowest root mean square error (RMSE = 0.66) at Cileungsi Station. In contrast, the lowest R2 = 0.02, and the highest RMSE = 3.74 at Pondok Gede Permai (PGP) Station. The results reveal a concerning trend of worsening 5-year flood events, with the 2025 flood reaching a peak inundation depth exceeding 3 m and affecting an area of 2.97 km2, caused by a rainfall threshold of more than 180 mm/day. Furthermore, the model shows a rapid hydrological response, with a time lag of approximately 7 h or less between peak rainfall and flood onset across three monitoring stations. Analysis indicates these severe floods were primarily triggered by heavy rainfall combined with significant land cover changes. The findings provide valuable insights for flood prediction and mitigation strategies in this vulnerable region.

The Indonesian Government have decided to relocate the capital city of Indonesia from DKI Jakarta to East Kalimantan Province in 2024. This new capital city of Indonesia called Nusantara Capital City (IKN) presents strategic issues regarding the lack of water availability and hydrometeorological disasters. Continuing the previous study about statistical comparison of rainfall extremes between Jakarta and IKN, this study on drought in IKN aims to investigate the water availability's condition by using drought index associated with rainfall intensity and number of no rain days. We analyze the trend of consecutive dry days (CDD), The highest one-day rainfall (RX1day), and Simple Precipitation Intensity (SDII) indices yearly and seasonally. The ground-based daily rainfall data at Sepinggan, Samarinda, Penajam Paser Utara, Balikpapan, and Sepaku during 1979-2022 (42 years) are used in this study. The Mann-Kendall method is carried out to detect the trend of each index. The preliminary results show that in general CDD shows no trend tendency over all stations. However, we found a tendency of a decrease CDD in Dec-Feb (DJF) and Sep-Oct (SON) indicating these periods have generally have no rainy days overall resulting in decreasing CDD relative to other seasons. However, the CDD tends to show a slight increase trend between 1980 and 2009. In 1997, the CDD index was exceptionally high coincided with El Nino event. In contrast, the SDII and RX1day tend to increase in Jun-Aug (JJA). This study has found that the yearly decreasing trend of CDD does not simply conclude that there is no contribution of CDD to drought events. Instead, the drought might be more related to high occurrence of CDD influenced by large scale events depending on season and topography. This research has provided basis knowledge about CDD associated with drought and should be beneficial to develop strategic plan for water availability and its impact on the forest fire mitigation management as well as reducing the hydrometeorological disasters which commonly occur over IKN and its surrounding areas.

The short-lived tropical squall lines could trigger weather-related hazards to the northern part of the Indonesia Maritime Continent (IMC), such as Sumatra and Kalimantan. Herein, we investigated the rare propagation event of the long-lived Sumatra squall line associated with a severe storm surge that induced coastal inundation in Java-Bali with devastating impacts from 22 May-2 June 2020. With a comprehensive approach combining observational, numerical, and analytical studies, for the first time, we proposed the possible mechanism related to the long-lived squall line over the IMC, which represents the largest equatorial tropical region with the most complicated air-sea interaction area in the world. Our findings suggest that the long-lived squall line related to the supercell-like thunderstorm initiated from multicell over central Sumatra on May 20, 2020, continuously propagated southeastward until several days later reached Bali. The near-quasi steady convective line has 6 hours of time travel from central Sumatra to west Java. The supercell-like rapidly develops from multicell with a deep convective updraft under the strong and fast cold pool (similar to 13.8 m s(-1)). The further southeastward propagation of squall line with broken line type seems reinforced by low-level moist transport from the Java Sea. This study also suggested that this unusual event of a long-lived squall line might occur more frequently in the warming upper ocean in the IMC.

Intense precipitation events are the main cause triggering hydrometeorological hazards over complex terrain. Two extreme precipitation (EP) events led to major flooding on 23-25 March 2021 and produced a rain-hail mixture (RHM) on 11 April 2021 in the Greater Bandung (GB) basin area, Indonesia. We investigated the spatial and vertical structure of precipitating cloud systems and the plausible mechanism triggering the two case studies with combined multiple remote sensing observations using an X-band polarimetric Doppler Weather Radar (Xpol) and Xband rain scanner radar (RSR) network, supported by rain gauges and satellite observation. The local processes controlling the intense rainfall events over the complex topography were quantified for the first time using an observational campaign in Indonesia. During the first EP event (23-25 March 2021), the modified satellite algorithm successively confirmed that the mesoscale convective system triggered the local anomalous circulation. The RSR network reveals that the EP in eastern GB contributed to the overflow of the Citarum River alongside the basin, coinciding with the eastward propagating convective system that produced oblate-shaped water droplets without hail. Nevertheless, during the second EP event on 11 April 2021, the strengthening of mountain-based convection played a main role in producing RHM, confirmed by a hail differential reflectivity larger than 12 dB and exhibited hail early stage over two height levels in different locations (981 m and 1033 m) in the GB. Our study also found Doppler vorticity-based and rain sizes combination indicators using RSR data networks in capturing such extreme weather events over complex topography with 35 min early times to support the early warning system of hydrometeorological disaster mitigation over GB, Indonesia.

This research investigates the statistical properties of rainfall extremes (REs) over Jakarta and Kalimantan using daily rainfall gauges during 1980–2008 (28 years). The results show that in the Megacity Jakarta, the maximum intensity of 95th and 99th percentile of rainfall is 65 and 120 mm, respectively, and is larger compared to Kalimantan (62 and 100 mm, respectively). However, the intense REs over Jakarta occur less frequently compared to Kalimantan. In contrast, there is a lower intensity of REs over Kalimantan, but they are more frequent than Jakarta. Both over Jakarta and Kalimantan, frequency of REs varies and is influenced by season. In the dry season, the frequency of REs over Kalimantan is about two times higher than frequency of REs over Jakarta. By using the ERA-5 reanalysis datasets, patterns of wind speed and directions are different with the strong westerly wind prevailing around Jakarta. Meanwhile, the strong westerly wind and southwesterly winds exist in the western and northeastern parts of Kalimantan, respectively. Different wind features might be one of the causes of the different nature of REs over both regions.

Supporting the Weather Modification Technology operating over Citarum Basin in October–November 2021, several rainfall observation instruments were installed around Bandung Area. Those instruments include X-band dual-polarization weather radar, Laser Precipitation Monitor (LPM) or laser disdrometer, and Automatic Weather Station (AWS). This study explored the rainfall characteristics around the Bandung area during November 2021. AWS was used to show accumulated rainfall amount; weather radar data was used to explore and analyze precipitation development mechanism both in temporal and spatial resolution; meanwhile, an LPM disdrometer was used to measure microphysics parameters of the rainfall such as the raindrop size and the number of raindrops, the velocity of the raindrops, reflectivity, and rainfall intensity. The temporal resolution of the weather radar was 5 min, the AWS was 5 min, and the LPM was 1 min. From the AWS data, the rainfall amount in November 2021 was recorded at around 491.5 mm, and the rainfall events mainly occurred in the afternoon until nighttime (11.00–22.00 LT). Data analysis from LPM (rainfall intensity, drop size, and number) showed that rainfall events from the convective or stratiform clouds over the Bandung area occurred in November 2021. Finally, cloud and precipitation development analyzed by weather radar data showed precipitation/cloud movement mainly propagated from North–North East to South, South–West, and West areas. Precipitation development from the south area also propagated to the Northern Bandung. Exploring and analyzing the microphysics characteristics of precipitation would help to determine the most suitable areas for cloud seeding activity.

A 4-day-flood occurred in Jakarta Province, Indonesia at the end of 2019 caused severe moral and material losses and weakened the economy. Various flood risk management methods are available to mitigate this damage. Assessing flood risks is thus an essential task for disaster management activities. An accurate flood risk map is required to be developed. In this research, we developed an economic valuation of flood risk that combines a quick flood map with the consequences of flooding using the Multi – Criteria Decision Analysis (MCDA) in the DKI Jakarta area. A quick identification of flood zones was carried out using SAR (Synthetic Aperture Radar). We estimated that about 54.10 km2 area was flooded area with a total economic loss about 1.406 trillion rupiahs. The sector of construction (10.10%), manufacturing (11.51%), wholesale, rental trade and repair of vehicles (13,90%), business activities (6.77%), financial & insurance (7.33%), and information & communication (7.6%) are major affected sectors that contributes 56.86% of the total economic loss from the market value. 20.49%-other service activities implicitly underestimate the value of environmental services and human productivities. To understand this, a detailed analysis of non-market value is needed in understanding the actual total economic loss.

Recurrent flooding in Jakarta and surrounding areas due to extreme rainfall is simulated by using distributed hydrological model. In the previous studies, the Rainfall-Runoff Inundation (RRI) model has been used for the flood simulation with 1-km spatial resolution, but it has not been comprehensively investigated. In this paper, extreme rainfall data derived from satellite rainfall data of GSMaP, topography, and land derived from the satellite remote sensing data are used as an input for the RRI model. We analyse the flood simulation at Ciliwung River Basin during 6 (Six) periods of extreme rainfall during January – March 2022 and divide between Flood (F) and Non-Flood (NF) periods. We found that the inundation occurred when the rainfall average reaches more than 7.3 mm/hr and concentrated in the Jakarta downtown area, which had induced the inundation around the Ciliwung river basin.

Jakarta, a megacity in Indonesia, experiences recurrent floods associated with heavy rainfall. Characteristics of subdaily rainfall and the local factors influencing rainfall around Jakarta have not been thoroughly investigated, primarily because of data limitations. In this study, we examine the frequency and intensity of hourly and daily rain rate, including spatial characteristics and variations across time scales. We use 6-min C-band Doppler radar and 1-min in situ data during 2009-12 to resolve spatial rain-rate characteristics at higher resolution than previous studies. A reflectivity-rain rate (Z-R) relationship is derived (Z = 102.7R(1.75)) and applied to estimate hourly rain rate. Our results show that rain rate around Jakarta is spatially inhomogeneous. In the rainy season [December-February (DJF)], rain rate exhibits statistical properties markedly different from other seasons, with much higher frequency of rain, but, on average, less intense rain rate. In all seasons, there is a persistent higher hourly and daily mean rain rate found over mountainous areas, indicating the importance of local orographic effects. In contrast, for hourly rain-rate extremes, peaks are observed mostly over the coastal land and lowland areas. For the diurnal cycle of mean rain rate, a distinct afternoon peak is found developing earlier in DJF and later in the dry season. This study has implications for other analyses of mesoscale rain-rate extremes in areas of complex topography and suggests that coarse-grain products may miss major features of the rain-rate variability identified in our study. Significance StatementFor many years, Jakarta and its surrounding regions have been repeatedly inundated by flooding triggered by short-duration heavy rainfall or rainfall accumulated over multiple days. Little is known about the distribution of local rainfall and how it differs between seasons. In this study, we used high-resolution C-band Doppler radar during 2009-12 to understand the characteristics of rainfall over this complex topography. The results demonstrate that the rainfall features vary spatially and seasonally. In the wet season, rainfall is more frequent but, on average, lighter relative to other seasons. In all seasons, the highest hourly and daily mean rain rate persistently occurs over the mountains, indicating the vital role of topography in generating rainfall in the region.

This archive consists of the post-processed data of C-Band Doppler Radar (CDR) over Jakarta and surrounding regions for the studies of "Variability of Jakarta Rain-Rate Characteristics Associated with the Madden-Julian Oscillation and Topography" and "Subdaily Rain-Rate Properties in Western Java Analyzed Using C-Band Doppler Radar". The dataset is a gridded rainfall data derived from the local relationship of Z (reflectivity) from the CDR and rainfall (R) from stations. The derived rainfall data are in daily estimates from 2009 to 2012 with the format in NetCDF files. The CDR data were obtained from the projects “Hydrometeorological Array for Intraseasonal Variation-Monsoon Automonitoring (HARIMAU)” (JFY 2005-2009), and the Science Technology Research Partnership for Sustainable Development (SATREPS) “Maritime Continent Center of Excellence (MCCOE) (JFY 2009-2013) of the Japan Science and Technology Agency (JST)/Japan International Cooperation Agency(JICA) under a collaboration of the Agency for the Assessment and Application of Technology (BPPT)-Indonesia and Japan Agency for Marine-earth Science and Technology (JAMSTEC)-Japan.

Flood disasters in Bekasi City almost occur every year, especially during high rainfall with a fairly long duration. Repeated flooding events due to extreme rainfall in Bekasi River Basin can be simulated using a distributed hydrological model. Rainfall-Runoff Inundation (RRI) model is a two-dimensional hydrological model capable of simulating rainfall-runoff and flood inundation simultaneously. The input data used in this study is extreme rainfall data derived from GSMaP satellite rainfall data, topography, and land derived from satellite remote sensing data. In this paper, we analyze the flood simulation in the Kali Bekasi watershed when extreme rainfall occurred on July 14, 15 and 16, 2022. On that date we found flooding in several areas including the Bekasi River Basin. From the results of the flood simulation data processing, it is then calculated how much economic loss due to the flood disaster occurred.

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.

Research on the interaction between the Madden-Julian oscillation (MJO) and rainfall around Jakarta is limited, although the influence of the MJO on increased rainfall is acknowledged as one of the primary causes of flooding in the region. This paper investigates the local rainfall response around Jakarta to the MJO. We used C-band Doppler radar in October-April during 2009-12 to study rain-rate characteristics at much higher resolution than previous analyses. Results show that the MJO strongly modulates rain rates over the region; however, its effect varies depending on topography. During active phases, MJO induces a high rain rate over the ocean and coast, meanwhile during suppressed phases, it generates a high rain rate mainly over the mountains. In phase 2 of the MJO we find the strongest increase in mean and extreme rain rate, which is earlier in the MJO cycle than most studies reported, based on lower-resolution data. This higher rain rate is likely due to increases in convective and stratiform activities. The MJO promotes more stratiform rain once it resides over Indonesia. In phase 5, over the northwestern coast and western part of the radar domain, the MJO might bring forward the peak of the hourly rain rate that occurs in the early morning. This is likely due to a strong westerly flow arising from MJO superimposed westerly monsoonal flow, blocked by the mountains, inducing a strong wind propagating offshore resulting in convection near the coast in the morning. Our study demonstrates the benefits of using high-resolution radar for capturing local responses to the larger-scale forcing of the MJO in Indonesia. Significance StatementRainfall in Jakarta and its surroundings is highly variable and often heavy resulting in devastating floods. In this region, in the wet season, rainfall is influenced by large-scale climate variability including the Madden-Julian oscillation (MJO) characterized by eastward propagation of clouds near the equatorial regions on intraseasonal time scales. The MJO has been known to increase the probability of rainfall occurrence and its magnitude, but we show that the impact differs in varying topography. The frequency and intensity of rainfall increase over land areas including mountains even when MJO has not arrived in Indonesia. Meanwhile, once MJO moves through Indonesia, the frequency and magnitude of the rainfall increases over the northern coast and ocean as well as in the west of the radar domain.

Over the Jakarta region, research on variability of local rainfall is very few due to relatively sparse observational datasets available. On the other hand, understanding the development of localized rainfall is necessary, particularly for reducing floods associated with heavy rainfall that commonly occur in the region. This study investigates the characteristics of rainfall using high spatial (0.1° x 0.1°) and temporal (30 minutes) resolutions of Global Precipitation Measurement (GPM)-IMERG data during 2009-2012. We found that this dataset is beneficial to examine spatial characteristics of local rainfall over the region. The peak of diurnal cycle of rainfall is larger in the rainy season Dec-Feb (DJF) compared to other seasons and is consistent with the results from weather radar. Background atmospheric conditions have shown that in DJF, a higher rainfall magnitude and frequency over the region are persistent over the mountain and are coincident with a stronger updraft of the air and dominant westerly wind. The GPM-IMERG data might be helpful in analyzing relatively detailed spatial rainfall, particularly in other parts of region over the Indonesian Maritime Continent (IMC) where dense observational datasets are spatially limited.

Heavy rainfall has been known as one of the factors inducing hydrometeorological hazards over the Megacity Jakarta. However, research on changes in rainfall extremes (REs) is somehow very limited in the region. This study will investigate annual and seasonal of REs and how it varies with different topography. We used daily rainfall record at nine observational sites (1975-2016) and reanalysis data of ERA INTERIM (1979-2016). The result shows that the severest rainfall (maximum of consecutive 5-day rainfall/RX5day and 99th percentile/R99p) has strong positive trends particularly at Kemayoran (coastal site) although the increased trends are also found at any other stations over the inland and mountainous areas. The analysis of seasonal trends demonstrates that significant increasing trends only occur in the wet (Dec-Feb) and transitional season (Mar-May, Sep-Nov) over Kemayoran (the coastal station) while a positive trend is observed in all seasons over Citeko (the mountain site). Compared to the wet season, in the dry (Jun-Aug) and transitional (Sep-Nov) seasons, there is concentrated areas near Jakarta and its surroundings with a large standard deviation in Mean Sea Level Pressure (MSLP), Outgoing Longwave Radiation (OLR) as well as cloud cover indicating that this region has a larger variability than the average. A distinct season of increased rainfall trends between the coast and mountain along with high anomalies in the regional OLR, MSLP, and cloud cover in the dry season implies that the development of REs might as a result of an interaction between local topography and large-scale climate condition.