Floods hit Jakarta and several areas in Ciliwung-Cisadane Watershed. The rain that occurred on 31 December 2019 stopped briefly and continued until January 1, 2020. As a result, several areas were flooded for several days. It is said that the rain that occurred was the largest in history. At least the rainfall station at Halim Perdanakusuma Airport recorded a rainfall with an intensity of 377 mm/day. That makes a question about how much discharge was generated by the rainfall. This study was conducted to assess the flood discharge and the inundated area caused by the rain on 2020 new year's eve. The Rainfall-Runoff-Inundation (RRI) is utilized to simulate the flood discharge and inundation using the 1D-2D hydraulic-hydrology model. This model also calculates infiltration and subsurface flow with the Green-Ampt equation. Besides, the rainfall data uses rain data recorded by the ground station and the topography uses SRTM data from the United States Geological Survey (USGS). Then, the flood discharge obtained from the model is compared with the flood return period. The return periods of the flood that are compared are 2, 5, 10, 25, 50, and 100 years. The result shows that the flood that occurred on 1 January 2020 is equivalent to flooding with a return period of 50 years.