*2.2. Data*

### 2.2.1. Precipitation Data

Precipitation data were collected from 24 rainfall stations in the Ciliwung–Cisadane Watershed during the flood event (Table 1). All of the rain stations are located around the study area, as shown in Figure 2a,b, which presents the rainfall distribution throughout the river area using the Inverse Distance Weighted Interpolation (IDW) method. The IDW method is the most frequently used deterministic method and can be applied for data whose distribution is characterized by a very large range [44]. From the data, the maximum rainfall during the studied event reached 376 mm. This condition is higher than the predicted rainfall for a 100-year return period in Halim Station, which was 340 mm [45].

**Figure 2.** Rainfall datasets in the study area. (**a**) Rainfall station locations. (**b**) Rainfall distribution on 1 January 2020.


**Table 1.** List of rainfall stations.

The predicted return-period rainfall was utilized as input in a calibrated model to determine the characteristics of various return periods of flooding. The calculation for return periods of rainfall was developed by Januriyadi et al. [42]. Our forecasting used a BMKG (Meteorological and Geophysical Institution of Indonesia) rainfall dataset for the period of 1986–2010 as a reference. The data were distributed throughout the study area, as presented in Figure 3. Compared with the rainfall that occurred on 1 January, the maximum rainfall of that event exceeded the maximum data in a 100-year period, which corresponds well with the previous study.

**Figure 3.** Rainfall return-period datasets. (**a**) Rainfall return-period of 2 years. (**b**) Rainfall returnperiod of 5 years. (**c**) Rainfall return-period of 10 years. (**d**) Rainfall return-period of 25 years. (**e**) Rainfall return-period of 50 years. (**f**) Rainfall return-period of 100 years.
