Events

12.052021

Precursors of disaster

Extreme rainfalls, deadly floods, and dangerous landslides are the threats that the inhabitants of Indonesia are to face in the rainy season that lasts six months in this climate zone - from October to April.

In January 2019 alone, flooding killed as many as 70 people on Sulawesi Island. As it turns out, we have appropriate research methods that allow us to read the harbingers of given phenomena and estimate the time of their occurrence.

What caused the heavy rainfall?

Research carried out at the Institute of Geophysics PAS by PhD student Beata Latos and dr Dariusz Baranowski from the Department of Atmospheric Physics, as part of international cooperation (PL-France-USA-Indonesia-UK) has shown that heavy rainfall and devastating flooding  was triggered by a “perfect storm”, when three different tropical weather systems all arrived there simultaneously. The largest of these weather systems, known as the “Madden-Julian Oscillation”, moved slowly eastward from the Indian Ocean over Indonesia. Embedded within this, two smaller weather systems, a “Kelvin wave” and a “Rossby wave”, also developed and arrived over Sulawesi, which resulted in rains of extraordinary strength and intensity. Further analysis of 20-year weather data revealed that  the probability of flooding when a Kelvin or Rossby wave was involved was twice as high as normal, increasing to as much as eight times when they occurred simultaneously.

Why is it crucial?

Based on weather forecasts, we are able to predict the upcoming phenomena (Madden-Julian oscillation, Kelvin wave and "Rossby wave) several days ahead, and thus warn about a potential danger. Such information can be crucial  for local authorities and emergency services to take appropriate steps to save the lives and health of residents.

We encourage to read the whole article:  Latos, B., Lefort, T., Flatau, M., Flatau, P., Permana, D., Baranowski, D., Paski, J., Makmur, E., Sulystyo, E., Peyrille, P., Feng, Z., Matthews, A., & Schmidt, J. (Accepted/In press). Equatorial waves triggering extreme rainfall and floods in southwest Sulawesi, Indonesia. Monthly Weather Review. https://doi.org/10.1175/MWR-D-20-0262.1

Researchers are from Poland (Institute of Geophysics Polish Academy of Sciences), France (École Nationale de la Météorologie, Centre National de Recherches Météorologiques), USA (Naval Research Laboratory, Scripps Institution of Oceanography, Pacific Northwest National Laboratory), Indonesia (Agency for Meteorology, Climatology and Geophysics of the Republic of Indonesia) and UK (University of East Anglia).The research is part of the Years of the Maritime Continent and  the Equatorial Line Observations (ELO) project.

 

  • Airplane window view for Makassar, fot. Beata Latos Sulawesi is the fourth largest and third most populated of the Indonesian islands. Makassar is the capital and the largest urban area of the island, as well as the 8th biggest city in Indonesia with a population of nearly 1.5 million. The city is located west of a mountain chain and is adjacent to the Java Sea. This area constitutes the south-western Sulawesi region, which is particularly prone to flooding. In this region, between 1999 and 2018, nearly half of all natural disasters (46%) were floods. In January 2019, southwest Sulawesi, including Makassar, experienced its largest flood on record.

    Airplane window view for Makassar, fot. Beata Latos Sulawesi is the fourth largest and third most populated of the Indonesian islands. Makassar is the capital and the largest urban area of the island, as well as the 8th biggest city in Indonesia with a population of nearly 1.5 million. The city is located west of a mountain chain and is adjacent to the Java Sea. This area constitutes the south-western Sulawesi region, which is particularly prone to flooding. In this region, between 1999 and 2018, nearly half of all natural disasters (46%) were floods. In January 2019, southwest Sulawesi, including Makassar, experienced its largest flood on record.

  • Diagram: Right panels: schematic depiction of the key processes responsible for extreme rainfall events and floods in southwest Sulawesi 3 days before (day-3), a day before (day-1) and during the event (day0). Abbreviations are: C - convergence in the Kelvin Wave, ER - Equatorial Rossby Wave, LLJ - Low-Level Jet, SV - Sumatra Vortex. Background are winds at 850hPa, solid line represents the Equatorial Rossby Wave vortex, dashed line represents cross-equatorial flow. The location of the mesoscale convective system is qualitatively depicted by an ellipse. Left panels: time evolution of approximated zonal wind anomaly (m/s, green line) and precipitation (mm, purple line) in southwest Sulawesi area.

    Diagram: Right panels: schematic depiction of the key processes responsible for extreme rainfall events and floods in southwest Sulawesi 3 days before (day-3), a day before (day-1) and during the event (day0). Abbreviations are: C - convergence in the Kelvin Wave, ER - Equatorial Rossby Wave, LLJ - Low-Level Jet, SV - Sumatra Vortex. Background are winds at 850hPa, solid line represents the Equatorial Rossby Wave vortex, dashed line represents cross-equatorial flow. The location of the mesoscale convective system is qualitatively depicted by an ellipse. Left panels: time evolution of approximated zonal wind anomaly (m/s, green line) and precipitation (mm, purple line) in southwest Sulawesi area.

  • Map: Orography (m) of the Western and Central Maritime Continent. Significant locations referred to in the main text are marked.

    Map: Orography (m) of the Western and Central Maritime Continent. Significant locations referred to in the main text are marked.