Citarum watershed is one of the national priority watersheds. Watershed health assessment activities are used as a reference in efforts to restore watershed conditions and improve watershed management planning. The watershed health was assessed for the Upper Citarum watershed in West Java, Indonesia. Three indicators, including hydrology and land cover were used to assess the watershed health. Hydrology indicators include the Annual Flow Coefficient (KAT) and River Regime Coefficient (KRA). Watershed health level assessment was conducted using Analytical Hierarchy Process (AHP) scoring method. Watershed health levels such as very unhealthy, unhealthy, moderately unhealthy, healthy, and very healthy were obtained by calculating each indicator total number of scores. From the health assessment result of The Upper Citarum watershed, the Annual Flow Coefficient indicator shows an unhealthy level, and River Regime Coefficient indicator shows very unhealthy level. In addition, the land cover indicator shows unhealthy level. Thus, because of a decreased vegetation cover over ten years. Based on the AHP weighting, it was found that The Upper Citarum watershed is at a very unhealthy level. Therefore, according to government regulations about proper watershed management, land cover vegetation must be managed to increase conservation and water quantity to maintain the Citarum watershed’s sustainability.

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.

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.