Washington: Rainfall from the Asian summer monsoon, which influences water availability, ecosystems and agriculture in India, has been decreasing over the past 80 years, according to a study. Man-made atmospheric pollutants are likely the reason for the decline unprecedented in the last 448 years, said researchers from the University of Arizona in the US.
The study, published in the journal Geophysical Research Letters, used tree ring records to reconstruct the Asian summer monsoon back to 1566.
The study found the monsoon has been weakening since the 1940s, resulting in regional droughts and hardships. The 80-year decline in the monsoon coincides with the ongoing boom in industrial development and aerosol emissions in China and the northern hemisphere that began around the end of World War II, according to the study.
Previous studies have looked at tree ring chronologies from this region but the new study, “surpasses in terms of the timespan covered and the number of trees involved,” said Steve Leavitt, from the University of Arizona in the US. “We were able to gather nearly 450 years worth of tree ring data with clear annual resolution from an area where tree ring growth correlates very strongly with rainfall,” Leavitt said.
Nearly half of the world’s population is affected by the Asian summer monsoon, which dumps the majority of the continent’s rainfall in a few short, torrential months. Summer rainfall has been declining in recent decades, influencing water availability, ecosystems and agriculture from India to Siberia.
Instrumental and observational records of monsoon strength and annual precipitation only go back about a hundred years. Long-term paleoclimate records are needed to help determine whether this decline is due to anthropogenic factors such as aerosol pollution or natural variation in the monsoon cycle. Several factors are thought to affect the strength of the Asian Summer Monsoon, including solar variability, volcanic eruptions and anthropogenic aerosols.
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