Experts dismissed a rumor spreading on the Internet that the drought in Chongqing was related to the Three Gorges Project as a "story without any scientific basis."
Sichuan's Bureau of Meteorology and Geophysics (BMG) reported on Thursday that the high temperatures and drought in Sichuan Province are the most severe since the BMG began keeping meteorological records in 1951.
The Sichuan BMG believes the high temperatures and drought partially reflect global climate change, which is leading to more frequent and extreme weather, a trend exemplified by the series of coastal typhoons that have hit China. These recent coastal typhoons are a major cause of the region's heat wave. Kept down by the typhoon, the subtropical high cannot move forward. As a result, it has been controlling most parts of Sichuan for some time.
The typhoon obstructs water vapor coming in from the south while the subtropical high holds up cold air from the north. Sichuan has become isolated meteorologically. In these circumstances, there is not enough precipitation to end the drought.
Sichuan is a basin. The extent of the drought varies throughout the province. The western area of the basin, which neighbors the Qinghai-Tibet Plateau, has more air collisions. These produce thunderstorms which alleviate drought. The eastern and central areas of the province are mostly hilly. With no mountains to raise air currents, very little rain is produced. Consequently in these areas the drought is more serious.
The Sichuan BMG said that the recent showers in the northwest of the province were the result of localized convectional precipitation. Although the temperature decreased slightly following the rain, hot weather is expected to dominate the region. Weather forecasting does not foresee any rainfall before the 20th of the month. Cities within the basin will still be subjected to high temperatures and the drought will not break.
The Chongqing BMG reminded the public that there were similar droughts in Sichuan in 1959, 1966, 1972, 1992 and 2001, and explained that this year's drought has been caused by unusual atmospheric circulation.
There are reports that the Western Pacific subtropical high has been unusually strong this summer with the ridge line positioned to the north and the west. Chongqing, affected by high pressure systems has reported more frequent sinking air currents and less precipitation. Consequently, the drought persists.
Circulation in middle and high latitude areas, such as the Ural Mountains and north-east Asia, is free of high pressure obstruction. There is insufficient rainfall because cold air fronts are weaker than usual.
Furthermore, the high pressure coming off the Qinghai-Tibet Plateau is stronger than usual. It combines with the subtropical highs to form a high pressure belt which is now controlling most parts of Chongqing. Middle and lower level transport channels for water vapor coming from the Bay of Bengal are blocked by a high pressure belt. Consequently there is very little water vapor, humidly is very low and the situation has resulted in drought.
By People's Daily Online