Tuesday, May 8, 2012

New paper finds extreme floods and droughts occurred in China when CO2 was "safe"

A paper published today in The Holocene finds "extraordinary droughts and floods were parts of the [entirely natural] climate variability" in Northwest China between 3200 and 3000 years ago during the mid-Holocene Climatic Optimum. The paper examines sedimentary records to document flooding 4.5 to 5 times the size of the largest measured flood since 1934. The paper adds to thousands of others documenting natural 'climate change' and extraordinary 'extreme weather' prior to any possible effect of man-made CO2. 
The Minoan Warming Period [mid-Holocene Climatic Optimum] occurred about 3000 years ago. Image from  Only 9.098 of the last 10,500 years were warmer than 2010.
Sedimentary records of extraordinary floods at the ending of the mid-Holocene climatic optimum along the Upper Weihe River, China
    1. Chun Chang Huang
    2. Jiangli Pang
    3. Xiaochun Zha
    4. Yali Zhou
    5. Hongxia Su
    6. Honglian Wan
    7. Benwei Ge
    1. Shaanxi Normal University, P.R. China
    1. Chun Chang Huang, Department of Geography, Shaanxi Normal University, Xi’an, Shaanxi 710062, P.R. China. Email: cchuang@snnu.edu.cn


    Sedimentary records of the Holocene extraordinary floods were investigated in the upper reaches of the Weihe River, a major tributary in the middle Yellow River basin. Palaeoflood slackwater deposits (SWD) were identified at several sites on the riverbanks. These clayey silt beds are inserted into the Holocene aeolian loess-soil profiles and slope clastic deposits. They have recorded the extraordinary palaeoflood events which occurred between 3200 and 3000 yr BP [before the present] as dated by OSL method and checked by the archaeological remains of the Neolithic and Bronze Age retrieved from the profile. The minimum flood peak discharges were estimated at between 22 560 and 25 960 m3/s by using palaeohydrological methods. It is 4.5–5.0 times the largest gauged flood (5030 m3/s) that has ever occurred since 1934. The palaeoflood slackwater deposits were found inserted into the pedostratigraphic boundary between the late-Holocene loess (L0) and the mid-Holocene Luvisol (S0) in the riverbank profile. This indicates that the extraordinary flood events were synchronous with the pedogenic regression at the end of the mid-Holocene climatic optimum. The climatic proxies from the studied profile and the correlative profiles in the river valley and the Loess Plateau show that the pedogenic regression was forced by climatic aridity and intensified dust storms and dust falls in connection with monsoonal shift over the Yellow River basin at about 3100 yr BP. The extraordinary flood events were documented not only on the Weihe River, but also on the mainstream and other tributaries of the Yellow River. These suggest that both extraordinary floods and droughts were parts of the climatic variability during the monsoonal shift. These findings are of great importance in understanding the interactions between hydrological system and climatic change in the semi-arid and subhumid regions of the world.

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