Why does Bogor experience more frequent rain? The scientific explanation

Jakarta (ANTARA) - Bogor and rain are two things that are difficult to separate. In fact, the nickname ‘Rain City’ has become deeply embedded in the daily life of this city. It is not unusual for the Bogor region to be hit by rain while the sky in Jakarta remains clear.

But why, in reality, does Bogor experience more frequent rain compared to many other regions? It turns and is not merely a coincidence. Bogor’s geographical location provides several conditions that support the formation of clouds and rain.

One of the primary factors is Bogor’s position, surrounded by mountainous areas. The city of Bogor is located in the western part of Java and is close to mountainous regions such as Mount Salak and Mount Gede-Pangrango. This topographical condition plays a role in the rainfall process, particularly through a mechanism known as orographic rainfall.

Simply put, when air carrying significant amounts of water vapour moves towards the mountainous region, the air is forced to rise following the slope’s contour. As the air rises higher, its temperature decreases. The water vapour then undergoes condensation and forms clouds. If the water content in the clouds is sufficient, rain can fall. This process allows areas surrounding mountains to receive higher rainfall compared to relatively flat regions. Research in Indonesia also shows that the orographic effect can increase rainfall in areas situated on the windward side.

Another factor is Bogor’s position, which is relatively open to the influence of sea breezes. Research from the Bogor Agricultural Institute (IPB) regarding rainfall characteristics in Bogor City mentions that the city is surrounded by mountains and open to sea breezes, resulting in relatively high rainfall. Sea breezes can bring air containing much water vapour towards the land. When this moist air meets atmospheric conditions that are supported and influenced by mountainous topography, the formation of rain clouds can become even more active.

Interestingly, rain in Bogor is not only frequent but also follows a quite distinct temporal pattern. Based on IPB research using data from 2017-2020, rainfall in Bogor City tends to increase from midday to night, peaking in the afternoon. During the period from December to February, rain can occur almost every hour. An increase in rainfall events is particularly visible around 15:00 to 18:00 WIB.

This pattern is related to the heating of the earth’s surface during the day. When the sun heats the surface, the air near the ground becomes warmer and rises. If the air is sufficiently moist, this process can trigger the growth of convective clouds. This is why a hot afternoon in Bogor does not always mean the afternoon will remain clear; rather, daytime heating can be part of the process that subsequently produces rain.

Although geographical conditions are a major reason, rain in Bogor is also influenced by broader atmospheric conditions. BMKG, in several weather analyses in West Java, noted several factors that can increase the growth of rain clouds, such as high air humidity, relatively warm sea surface temperatures, wind convergence or shifts, and unstable atmospheric conditions. This means that when these conditions coincide with Bogor’s local factors, the potential for rain can increase further.

Therefore, it is inaccurate to say that rain in Bogor is caused by only one factor. There is a combination of geographical location, mountains, water vapour supply from the sea, solar heating, wind, and atmospheric dynamics working together.

So, does it always rain in Bogor? Certainly not. The ‘Rain City’ nickname does not mean Bogor will be drenched every day or at all times. The intensity and frequency of rain still change according to the seasons and atmospheric conditions. IPB research shows that Bogor’s rainfall pattern also changes throughout the year. From December to February, rain can occur almost every hour, while from June to August, rain from night to early morning is much rarer.

Other research regarding rainfall patterns in several major cities in Indonesia also found that Bogor has a high percentage of wet months and relatively high annual rainfall compared to other studied regions. Thus, if a heavy rain suddenly arrives one afternoon while you are in Bogor, there is actually a long process that has been occurring in the atmosphere. Moist air arrives, the sun heats the surface, the air rises, the mountains assist the lifting process, clouds grow, and finally, water falls back to the surface as rain. In other words, Bogor is not ‘cursed’ to always be rainy. The city simply possesses a combination of geographical and atmospheric conditions that make rain relatively easy to form. That is the reason why an umbrella is a quite sensible item to always carry when active in Bogor.