《TAIPEI TIMES 焦點》 Plum rain likely to be delayed

WEATHER OR NOT: Postponed rainfall could be partly attributed to the pace of rising temperatures in the western Pacific Ocean, an NTNU research team has found

By Sean Lin / Staff reporter

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As the nation braces for phase-three water rationing — set to begin next week — a National Taiwan Normal University （NTNU） research team yesterday predicted a delay in the start of the plum rain season, and that the amount of rain would be reduced by 25 percent.

Citing data produced from surveys between 1982 and 2012, NTNU associate Earth science professor Huang Wan-ju （黃婉如） said the plum rain season has shortened from 20 days to about 15 days since 2008.

In addition, the data showed that cold air streams above the nation have grown weaker over the years, while hot air currents have moved north — from 23.1° north latitude to 25° north, where the streams collide to create the plum rain, Huang said.

The trend suggests that the chances of Taiwan receiving plum rain are diminishing, Huang added.

Also, seasonal rainfall has become stronger and more haphazard, increasing sediment buildup in reservoirs, making it difficult for them to store water and causing downpours to more frequently flow directly to the sea, she said.

She said the plum rain season has been pushed back from the middle of next month to the end of next month , which means that the nation is likely to experience longer periods of water shortages.

The phenomenon could be partly attributed to the pace at which temperatures are rising in the western Pacific Ocean — which is two to three times faster than in other areas in the world — since the same problems also exist in the southwestern coastal provinces of China, which are generally on the same latitude as Taiwan, she said.

Asked whether these problems would bring intensified periods of water supply shortages or possible droughts for southern Taiwan, Huang said that southern Taiwan still has convectional rains as a water supply source, and that the question could only be answered after further analysis.

Other findings by the research team include the growing occurrence of “dipoles,” polarized weather patterns on the eastern and western coasts of the US, as witnessed over the past two years.

Based on simulations of 17 weather patterns, Huang’s team discovered that a drop in coastal seawater temperatures in East Asia has changed atmospheric circulation, resulting in prolonged droughts and heavy snow in the US’ west and east coasts respectively.

Simulations also showed the researchers that the occurrences of dipoles relate to the amount of fossil fuels used in an area, indicating that the use of fossil fuels could have caused the extreme weather patterns.

新聞來源：TAIPEI TIMES