Climate change has affected the amount of rainfall in Indonesian islands, study suggests

The rainfall in some of Indonesia's islands such as Sumatra, Java, and Borneo affects the climate of regions that are even thousands of miles away, according to a new study.

Sumatra, Java, Borneo, and Papua New Guinea, along with a clutch of smaller islands are part of what is known as the "Maritime Continent," which, according to the researchers, experiences significant rainfall including "periodic monsoonal rain, and flash flooding." In the study, published in the Journal of Atmospheric Sciences, researchers revealed details of the connection between a larger atmospheric phenomenon called the Madden-Julian Oscillation (MJO), and the daily patterns of rainfall in the Maritime Continent.

The MJO, the study noted, circles the globe around the tropics and can affect weather on weekly to monthly time scales, bringing cloudy and sunny periods alternatively.

The researchers, led by atmospheric scientist Giuseppe Torri at the University of Hawaii (UH), found that the impact of the MJO on the daily rainfall patterns of Sumatra was quite significant. When the MJO was active near the Maritime Continent, there was more water vapour, and therefore greater possibility of rain, according to the researchers.

The study also noted that the MJO was linked to more variations in water vapour throughout the day in the Maritime Continent, as compared to a suppressed phase. During the active phase of the MJO, the study noted that clouds and rain tended to move offshore at night at a faster rate.

"Given the existing scientific literature, we had a sense that the MJO had an impact on the local convection in the Maritime Continent," said Torri. He added that he was surprised how well he could see the convection propagate offshore in the late evening. "This is thanks to the density of stations of the GPS network we considered," he said.

In June and early July 2019, a heatwave in Alaska broke temperature records, as seen in the 8 July air temperature map (left). The corresponding image from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on Aqua on the right shows smoke from lightening-triggered wildfires. Image: NASA

The researchers used location data from a network of GPS stations installed in Sumatra and on the neighbouring islands by a team of scientists interested in monitoring tectonic activity along the western coast of Sumatra.

They found that the GPS signal was distorted by the amount of water vapour in the atmosphere. The researchers then realised that the distortion recorded in the GPS stations could provide useful information about the state of the atmosphere.

The MJO, according to the researchers, could be one of the most important phenomena on the planet, influencing the weather and the climate of regions that are even thousands of miles away from the Maritime Continent.

The researchers emphasised that a better understanding of the MJO, and a good way to simulate it are very important for understanding the Earth's current and future climate trends.

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