Scorching Afternoons, But Chilly Nights? IPB University Professor Explains the “Bediding” Weather Phenomenon

In recent weeks, the air from night through morning in several regions of Indonesia, particularly on the island of Java, has felt cooler than usual. This condition is known as bediding or, in Javanese, bedhidhing. Is this a result of climate change? 

Dr Givo Alsepan, a professor in the Department of Geophysics and Meteorology at the Faculty of Mathematics and Natural Sciences (FMIPA) at IPB University, emphasizes that bediding is not directly caused by climate change. This phenomenon is part of seasonal climate dynamics that almost always occur between June and September.

Nevertheless, climate change can still influence the characteristics of bediding, such as the start of the dry season, air humidity levels, the frequency of clear nights, and the duration of cold temperatures.

A Normal Occurrence
“Bediding is a normal atmospheric phenomenon that occurs during the dry season. It does not exist in isolation but is a manifestation of physical atmospheric processes. This condition occurs when the daily minimum temperature drops significantly due to highly effective radiative cooling,” he explained.

He elaborated that the phenomenon is triggered by a combination of several atmospheric conditions commonly found during the dry season. One of the main causes is the tendency for clear skies at night. 

“The minimal cloud cover allows the heat absorbed by the Earth’s surface during the day to be more easily radiated back into the atmosphere and outer space, causing the air temperature near the surface to drop more quickly,” he explained.

In addition, the air during the dry season is generally drier than during the rainy season. The reduced water vapor content in the atmosphere means that less heat is retained, making the cooling process more effective.

“When the air is drier, heat is released from the Earth’s surface more effectively. As a result, the air from night through the early morning feels much cooler,” he said.

More Noticeable in High Altitude Areas
According to Dr Givo, these conditions will be more pronounced in mountainous and high altitude regions. In addition to being influenced by higher elevations, cold air also tends to flow into and accumulate in valleys. In fact, in areas like the Dieng Highlands, these conditions can trigger the formation of frost or hoarfrost.

The Australian Monsoon and El Niño
Another factor contributing to the cold spell is the influence of the Australian monsoon. During the dry season, Australia is experiencing winter, so the air masses moving toward Indonesia bring cooler and drier air, especially to regions south of the equator such as Java, Bali, and Nusa Tenggara.

“Indonesia is currently in the dry season, which is influenced by the Australian monsoon, while Europe, North America, and parts of East Asia are entering summer,” he explained.

According to him, the developing El Niño phenomenon also has the potential to intensify the dry conditions in Indonesia. Lower rainfall, decreased humidity, and clearer skies at night allow for more efficient radiative cooling, thereby increasing the likelihood of frost.

Stay Healthy
While this phenomenon persists, the public is urged to stay healthy, especially children, the elderly, and those with respiratory conditions. Cold, dry air can worsen symptoms of the flu, asthma, and respiratory tract infections.

The public also needs to ensure they stay adequately hydrated even when the weather feels cold, and remain vigilant about the risk of forest and land fires, which tend to increase during the dry season.

Dr Givo estimates that this phenomenon could potentially last until the peak of the dry season, around late July through August and in some areas, it may even continue into early September, depending on atmospheric conditions.

“The public need not worry excessively, as bediding is part of the seasonal climate cycle. The most important thing is to continue following weather and climate forecasts from the BMKG so that people can better anticipate changes in weather conditions,” he concluded. (IAAS/LAN)