Enviro News Asia, Bandung — A study by Indonesia’s National Research and Innovation Agency (BRIN) has identified the role of “cold pools” in sustaining rainfall and contributing to extreme rain events in several parts of Indonesia.
A cold pool is a layer of relatively cool air near the surface surrounded by warmer air. According to Erma Yulihastin, a researcher at BRIN’s Research Center for Climate and Atmosphere (PRIMA), the phenomenon can trigger new rain cells and prolong existing rainfall systems.
Erma presented the findings during EARTH School 2026 at the Samaun Samadikun Science and Technology Center in Bandung on September 22, 2026. The event, held from September 21 to 25, was organized by BRIN in cooperation with the Research Institute for Sustainable Humanosphere (RISH) at Kyoto University, Japan.
She explained that persistent rainfall lasting more than two hours can contribute to the formation of a cold pool. As rain falls, some of the water evaporates and cools the surrounding air. The cooler air then spreads horizontally near the surface.
This movement can force warmer air around the cold pool to rise, triggering the development of new clouds and rain cells along its boundary. As a result, rainfall that is already occurring can help create atmospheric conditions for subsequent convection.
The finding highlights the dynamic nature of rainfall systems, in which existing rain can influence the development of further convection rather than simply being the final result of cloud formation.
Erma also linked the cold pool mechanism to nighttime rainfall in West Java, including Jakarta. Her study found that convective systems can develop over the sea at night before moving toward land.
The movement is influenced partly by northerly winds. When these winds are sufficiently strong, a cold pool that forms as a convective system begins to weaken can move toward the coast and help trigger new convection.
When northerly winds are weaker, however, the ability of the cold pool to generate new convection is reduced. The interaction between near-surface cool air and wind patterns therefore becomes an important factor in understanding rainfall development along the coastal and inland areas of West Java.
The influence of cold pools is also evident in other regions. In West Sumatra, Erma’s research examined interactions between cold pools and mountainous terrain.
The interaction can strengthen upward air movement, allowing convective cells to redevelop and rainfall systems to persist for longer periods. Such conditions can contribute to prolonged convective activity and extreme rainfall.
The findings indicate that local geography plays an important role in determining how rainfall systems develop. The same atmospheric mechanism can interact differently with wind patterns and topography, producing different rainfall characteristics from one region to another.
BRIN said the research demonstrates that rainfall development in tropical Indonesia is influenced not only by clouds and atmospheric moisture, but also by the movement of cooler air, wind conditions and topography.
Understanding how these factors interact can help researchers improve knowledge of rainfall dynamics and extreme weather events in Indonesia. (*)
