Improvement of Heavy Rainfall Simulated with SST Adjustment Associated with Mesoscale Convective Complexes Related to Severe Flash Flood in Luwu, Sulawesi, Indonesia

Abstract

Flash flooding is an important issue as it has a devastating impact over a short time and in a limited area. However, predicting flash floods is challenging because they are connected to convection systems that rapidly evolve and require a high-resolution forecasting system. In addition, modeling a case study of a mesoscale convective complex (MCC) is the key to improving our understanding of the heavy rainfall systems that trigger flash floods. In this study, we aim at improving modeling skills to simulate a heavy rainfall system related to flash-flood-producing MCCs. We simulated a heavy rainfall event related to a severe flash flood in Luwu, Sulawesi, Indonesia, on 13 July 2020. This flood was preceded by persistent heavy rainfall from 11 to 13 July 2020. In this case, we investigated the role of sea surface temperature (SST) in producing the persistent heavy rainfall over the region. Therefore, we explore the physical and dynamic processes that caused the heavy rainfall using a convection-permitting model with 1 km resolution and an experiment comparing the situation with and without updated SST. The results show that the heavy rainfall was modulated by the development of a pair of MCCs during the night. The pair of MCCs was triggered by a meso-low-pressure system with an anti-cyclonic circulation anomaly over the Makassar Strait and was maintained by the warm front passing between the sea and land over central Sulawesi. This front was characterized by moist–warm and cold–dry low-level air, which may have helped extend the lifetime of the MCCs. The north-westward propagation of the MCCs was due to the interaction between predominantly a south-easterly monsoon and SST anomalies. This study suggested that the long-lived (>10 h) MCCs (>80,000 km2 cloud shield) and persistent precipitation are reproduced well in the updated SST scenario in the WRF model. This relatively simple technique in the running model provides a new strategy for improving flash flood forecasting by better predicting rainfall as an input in the hydrological model. Our findings also indicated a long-lived MCC maintained by back-building mechanisms from night to morning inland as an exceptional MCC, which does not correspond to a previous study.

Propagation of tropical squall line-induced storm coastal inundation episodes in Java-Bali, Indonesia

“…The simulation configuration and scheme are summarized in Table 1 . The WRF model configuration follows earlier studies [ [20] , [21] , [22] ] that well-simulated the cold pool, propagating convective system, and heavy rainfall compared to satellite observation, respectively.…”

Upaya Pemerintah Kota Makassar dalam Mewujudkan Ketahanan Kota Pascabencana Banjir

“…Indonesia memiliki kriteria curah hujan yang tinggi sepanjang tahun (Lestari et al, 2019). Beberapa studi menemukan bahwa curah hujan yang tinggi dapat menyebabkan banjir (Yulihastin et al, 2021), terutama jika sistem drainase tidak mampu menampung air hujan yang berlebih (Dube et al, 2022). Tingginya populasi di beberapa kota besar di Indonesia juga dinilai ikut menyebabkan lahan yang terbangun dan sistem drainase tidak mampu menampung volume air yang dihasilkan (Handayani et al, 2020).…”

Flood Sedimentology for Future Floods Mitigation in North Luwu, Sulawesi, Indonesia

“…The flash floods have caused serious damage to settlements, infrastructure, and agricultural areas. The flow of scrapped materials carried by the flash floods resulted in thousands of houses being submerged and 4,000 families affected, along with dozens of people dying and several residents being declared missing [22][23][24]. The geological condition of the Masamba area is composed of an alluvial plain covering an area of approximately 40 × 20 km 2 , forming a lowlands morphology known as the Depression Zone, according to Simandjuntak et al (1991) [25].…”