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Atmospheric analysis before the flood in Garut on October 12, 2020
14 Oct 2020

The flood in Garut on October 12, 2020, is thought to have been due to heavy and continuous rain. Consecutive rains occurred in Garut from October 7, 2020 to October 12, 2020, causing rivers in Garut, especially the large rivers of Cilauteureun and Cipalebuh in Pameungpeuk District to no longer be able to accommodate rainwater. The river overflowed and there was a flood. Information compiled from Kompas media states that the areas affected by the flood include Neglasari, Cikelet, Cibalong, Pameungpeuk and Bungbulang. From this information it is known that the affected area stretches from north to south. The results of the analysis of the SADEWA DSS-based Quick Reaction and Disaster Analysis (TREAK) team showed that the DSS had predicted the rain sequence that occurred in Garut. On October 7, there was light rain during the day to be precise in the central to southern part of Garut (Figure 1). The next day (08 October 2020) it rained from noon to late afternoon in central Garut (Figure 2 above). Then it rained on October 9 with a long duration, from 13:00 to 19:00 WIB with high intensity (Figure 2 center). On October 10, the rain fell from 14:00 to 15:00 WIB (Figure 2 below). On October 11, the rain fell during the day from 12:00 to 15:00 WIB with low intensity and from 16:00 to 17:00 WIB with high intensity (Figure 3). Through SADEWA surface wind patterns, it is observed that the rain in Garut is due to small-scale convergence, namely the meeting of the northeast wind from the Java Sea and the southeast wind from the Indian Ocean (Figure 4). high. Rain that occurs in northern / central and southern Garut accumulates in rivers in the south such as the Cilauteureun river and the Cipalebuh river.


Figure 1 Spatial distribution of rain based on SADEWA on October 7, 2020


Figure 2 Spatial distribution of rain based on SADEWA on October 08, 2020, October 09 2020 and October 10, 2020


Figure 2 continued for 09 and 10 October 2020


Figure 3 Spatial distribution of rain based on SADEWA on October 11, 2020

Figure 4 Surface circulation based on SADEWA which creates convergence in the Garut region

Data on soil types in Garut (Source: consisting of yellowish red podsolics, yellow podsols and regosols are the largest area in the southern part, while in the northern part it is dominated by andosols as types of soil that are good for agricultural land. Regosol and podzolic soils are loose, so it is easy to erode. Podsolic is more loose than regosol. Thus, it is not only the high rainfall that needs to be watched out for in Garut but also the danger of landslides, especially in the southern part of Garut, especially when the rain continues to fall after the flood.

In line with the rain information from SADEWA, GSMAP satellite data shows that convection activity in Neglasari and Pameungpeuk was quite high on October 10, 2020, marked by falling rain on that date (Figure 5). Activity weakened on 11 October 2020 and was active again later on 12 October 2020. In Cikelet, the intensity of rainfall was observed as shown in Figure 6. The distribution of spatial rainfall observed with the GSMAP satellite also shows the presence of light to high intensity rain around Pameungpeuk Figure 7 left). The same conditions are also shown in (Figure 7 right)



Figure 5 Rainfall in Neglasari and Pameungpeuk from 10 October 2020 to 12 October 2020

Figure 6 Rainfall in Cikelet based on GSMAP from 06 to 12 October 2020

Figure 7 Distribution of rainfall in southern Garut on October 11, 2020 based on GSMAP (left), and based on (right)

Other data through COSMIC-2 satellite monitoring shows an increase in water vapor around Pameungpeuk since October 6, 2020, identified through Rossby Gravity waves moving from east to west (Figure 8).


Figure 8 Movement of Rossby Gravity waves from east to west as water vapor content increases over Garut (2 km) based on Hovmoller (left) and its spatial distribution (right)

Compiler: PSTA's Disaster Analysis Reaction Team (TREAK)

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