Researchers have developed a new technique to study the changes in winter monsoon rainfall in Southeast Asia over the past 8,000 years. The technique involves analyzing a stalagmite from a cave in central Vietnam, which contains clues about the seasonal patterns of precipitation in the region.
Asian winter monsoon
The winter monsoon brings heavy rains to many parts of Southeast Asia, causing floods and landslides that affect millions of people and damage agriculture and water resources. However, unlike the summer monsoon, the winter monsoon is poorly understood and has limited data from weather stations.
The new technique, published in the journal Nature Communications, allows researchers to distinguish between rainfall caused by local weather systems and rainfall influenced by regional atmospheric circulation. This helps them to reconstruct the past evolution of the winter monsoon and its relationship with the summer monsoon and other climate factors.
The researchers found that the regional component of the winter monsoon, driven by the difference in temperature between the land and the ocean, varied in sync with the summer monsoon and the solar heating of the Northern Hemisphere. However, the local component of the winter monsoon, driven by the moisture availability over the ocean, showed a different pattern and was more sensitive to changes in sea surface temperature and El Niño events.
Debate over Southeast Asia monsoons
Annabel Wolf, now a postdoctoral scholar at the University of California, Irvine’s Department of Earth System Science, said: “The past evolution of the winter and summer monsoons in Southeast Asia has been debated for decades.
“By examining this stalagmite from Vietnam, we were able to track autumn and winter rainfall over a significant period and, crucially, to differentiate between the rain which had fallen due to local weather systems and the rain caused by wider regional systems.
“Our main conclusion was that the regional component of the monsoon, caused by atmospheric circulation, shows a contradictory relationship between winter and summer monsoons, driven by insolation in the northern hemisphere.
“However, the results from the local rainfall samples showed a strong connection between summer and winter monsoons.”
Speaking about the research Dr Ersek said: “By shedding light on potential discrepancies in paleoclimate reconstructions, scientists now have a critical tool to refine their understanding of historical climate patterns.
“Our findings have the potential to inform policies and strategies aimed at mitigating the impacts of intense rainfall in Southeast Asia, which becomes more imperative as climate change continues to exert its influence on global weather patterns.”
Re-examine samples for weather insights
Now there is the possibility to re-examine samples from other areas of Southeast Asia, extract local and regional rainfall levels, and gain greater insight into how weather patterns change over time – the research findings enable this. It is also possible to evaluate how patterns have evolved and how they may change in the future.
In contrast to the well-studied southwest summer monsoon, there is no strong record of long-term changes in Southeast Asian rainfall associated with the northeast winter monsoon under pre-industrial conditions. This means that changes in rainfall in this region on a long-term basis are not well understood.
As a result, many climate models underestimate winter monsoon rainfall by as much as 50 per cent, leaving significant uncertainty in future climate projections.
The researchers said that our findings have the potential to inform policies and strategies aimed at reducing the impacts of extreme rainfall in Southeast Asia, which is becoming more urgent as climate change continues to exert its influence on global weather patterns.
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