Extreme Weather and Climate Change

KOMPAS/RENY SRI AYU

Access to landslide-affected locations in Bontomarannu district of Gowa regency, South Sulawesi, is inundated by overflow from Jenebarang River. In Gowa, extreme weather had raised water level in local dams above the normal condition. The local government declared the condition into the alert and asked residents affected by the flooding to evacuate.

South Sulawesi is known for high rainfall. However, province-wide rainfall of 100 millimeters per day, sometimes more than 300 mm per day, is highly unusual and can cause floods. The National Disaster Mitigation Agency (BNPB) said this was the second highest rainfall in South Sulawesi since 1998.

Lengkese village in Takalar regency saw the highest daily rainfall of 329 mm; Bawakaraeng, Gowa, saw 308 mm and Pettene in Marusu, Maros regency, saw 310 mm of daily rainfall. Makassar saw daily rainfall of 197 mm.

The Meteorology, Climatology and Geophysics Agency (BMKG) categorizes daily rainfall of 5 mm to 20 mm as light rain and 20-50 mm of daily rainfall as medium rain; 50-100 mm is heavy rain and more than 100 mm of daily rainfall is extreme rain.

“The [recent] extreme rain was caused by a combination of several meteorological factors,” said BMKG weather forecast head Agie Wandala Putra. The main cause was the Madden-Julian oscillation (MJO) – an air mass over the equatorial zone – moving to Indonesian waters, as well as the concurrent winter monsoon from the South China Sea and convergence zones over Australia.

Another factor was the growth of large supercell clouds caused by the Intertropical Convergence Zone (ITCZ). The ITCZ follows the sun’s relative position and thus affects the peak of the rainy season.

The weather can change quickly. “The trend of hydrometeorological disasters in Indonesia is increasing, from floods to tornadoes. Apart from improved data collection, the rain and climate patterns are also changing,” said BMKG climate and air quality information head Siswanto.

The rain pattern in South Sulawesi from 1981 and 2016 showed rainfall intensity of 20 mm per day, with increased rainfall of 0.1149 day per year and 1.149 day per decade.

The trend could lead to increased risk of flooding in Indonesia, especially in South Sulawesi. The disaster risk is further heightened by environmental degradation and higher residential density in floodplains.