Taipei [Taiwan], August 4 : About 200cm of rainfall fell in parts of southern Taiwan from Monday last week to 9am on Sunday, the Central Weather Administration (CWA) said, Taipei Times quoted.
Kaohsiung's Taoyuan District saw total rainfall of 2,205mm, while Pingtung County's Sandimen Township had 2,060.5mm and Tainan's Nanhua District 1,833mm, according to CWA data, as quoted by Taipei Times.
Meanwhile, Alishan in Chiayi County saw 1,688mm of accumulated rain and Yunlin County's Caoling had 1,025mm rainfall.
The Pingtung County Government said that 831 local residents have been pre-emptively evacuated from mountainous areas. A total of 576 are staying with relatives in low-lying areas, while the other 255 are in shelters.
CWA forecaster Chu Mei-lin said that three factors are contributing to the intensive rainfall in southern Taiwan.
The first is successive southwestern air currents that formed over the ocean and moved landward, impacting the western half of Taiwan proper and outlying Penghu County.
Second, southwesterly winds brought in unstable air that developed into convection currents over land and resulted in rain.
Third, the southwesterly winds sweeping into southern Taiwan's mountainous topography caused orographic rainfall, causing intense rain in the region's mountainous areas, Chu said.
Orographic rain is produced when moist air lifts as it moves over a mountain range, cooling as it rises and forming clouds that produce rain upwind of the mountain ridge, as per Taipei Times.
A large-scale low pressure system has been hovering over Taiwan since late July, resulting in persistent southwesterly winds, Chu said.
The intense rain peaked once from Monday to Thursday last week, with a second peak occurring over the weekend, she said.
The CWA has issued precipitation warnings through Sunday to Monday.
Extreme torrential rain advisories have been issued for mountainous regions in Tainan, Kaohsiung and Pingtung County, where accumulated rainfall exceeding 500mm in 24 hours is forecast, according to the CWA.
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