TEMPO.CO, Jakarta - Over the past few weeks, Indonesians, especially those in Java, have been experiencing frigid air that lasted overnight. This phenomenon, known in Javanese as 'bediding,' leaves the atmosphere colder than usual.
According to Givo Alsepan, a lecturer in the Department of Geophysics and Meteorology at the Faculty of Mathematics and Natural Sciences (FMIPA) of IPB University, the bediding phenomenon is not triggered directly by climate change, but is part of seasonal climate dynamics that almost always occurs from June to September.
But climate change certainly plays a part, he said, with the early onset of the dry season, the level of air humidity, the frequency of clear nights, and the duration of cold temperatures.
"Bediding is a normal atmospheric phenomenon that occurs during the dry season. It is not isolated, but a manifestation of atmospheric physical processes. This condition occurs when the daily minimum temperature drops significantly due to very effective radiative cooling," he said in a written statement on Monday, July 27, 2026.
What Causes Bediding?
Clear night skies are among the primary factors that make bediding, according to Givo. "The lack of cloud cover makes it easier for the heat absorbed by the earth's surface during the day to be radiated back into the atmosphere and outer space at night, causing the air temperature near the surface to drop more quickly," he added.
In addition, the air during the dry season is generally drier compared to the rainy season. The reduced water vapor content in the atmosphere allows heat to escape more easily, thus making the cooling process more effective.
"When the air is drier, the release of heat from the earth's surface is more effective. As a result, the air feels much colder overnight," he said.
According to Givo, this condition will be more pronounced in mountainous and highland areas. Besides being influenced by higher elevations, cold air also tends to flow and accumulate in valleys. In regions such as the Dieng Plateau, this condition can even lead to the formation of frost or frozen dew.
Another factor that reinforces bediding is the influence of the Australian monsoon winds. When Indonesia is experiencing the dry season, it is wintertime in Australia, so the air mass moving towards Indonesia brings cooler and drier air characteristics, especially to the southern equatorial regions such as Java, Bali, and Nusa Tenggara.
"Indonesia is currently in a dry season influenced by the Australian monsoon, while Europe, North America, and parts of East Asia are entering the summer season," he explained.
The likelihood of bediding is also strengthened by the El Nino phenomenon, which brings drier conditions in Indonesia. Lower rainfall, decreased air humidity, and clearer night skies make the radiative cooling process more optimal—an optimal situation for bediding.
During this phenomenon, the public is advised to maintain their health, especially for children, the elderly, and those with respiratory illnesses. Cold and dry air can exacerbate symptoms of influenza, asthma, and respiratory tract infections.
People are also advised to ensure adequate fluid intake even when the weather feels cold, and to be more vigilant against the potential for wildfire outbreaks, which tend to increase during the dry season.
The cold spell is expected to last until the peak of the dry season, around late July to August, and in some regions, it may persist until early September, depending on the development of atmospheric conditions.
"People need not worry since bediding is part of the seasonal climate cycle. The most important thing is to continue to follow weather and climate forecast information from BMKG in order to better anticipate changes in weather conditions," he concluded.
Read: El Nino Threat: What Will Jakarta Do During the Drought?
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