Wednesday, February 13, 2013

New paper finds largest floods in China occurred when CO2 was 'safe'

A paper published today in Palaeogeography, Palaeoclimatology, Palaeoecology finds extraordinary floods occurred in China during the Roman Warming Period that were twice the size of the largest flood ever recorded during modern times. The paper adds to many other peer-reviewed papers demonstrating that floods have been much more extreme in the past and there is no evidence of any human influence upon floods

Related: Historical Flood Trends in Europe

Extraordinary hydro-climatic events during the period AD 200−300 recorded by slackwater deposits in the upper Hanjiang River valley, China

  • Department of Geography, Shaanxi Normal University, Xi'an, Shaanxi 710062, P.R. China


The Hanjiang River, a major tributary of the Yangtze River in China, is noted for the current national South-to-North Water Diversion project. Palaeo-hydrological investigations were carried out along the upper reach gorges of the Hanjiang River that drains the Qinling and the Dabashan Mountains. A set of palaeoflood slackwater deposit beds (SWDs) was identified in Holocene pedo-stratigraphy of the riverbanks along the valley. These SWDs are interbedded in the eolian loess-soil profiles in the cliffy riverbanks and they thin out towards the upper slopes. The palaeoflood SWDs were differentiated from eolian loess and soil by the sedimentary criteria and analytical results. The minimum flood peak discharges were estimated to be 65,400−65,830m3 s- 1 by using palaeo-hydrological methods. They are about twice of the largest gauged flood (34,300 m3 s- 1) that has ever been measured. They represent the largest flood events in the upper reaches of the Hanjiang River over the Holocene. These extraordinary flood events were dated to 1810−1710 a (AD 200−300) with the optically stimulated luminescence method and checked by archaeological dating of the human remains retrieved from the profiles. This indicates that the extraordinary floods occurred during the dynasties of Eastern Han to Western Jin (AD 25−316) in Chinese history, during which severe droughts and floods were recorded in documents. In the reconstructed 2000-year temperature time series based on high-resolution climatic proxies from tree-rings, stalagmites, ice-cores and lake sediments from over the world, these extraordinary palaeoflood events are correlated with an increased climatic variability characterized by cooling and drying during the period AD 150−350. This result is important for understanding the effects of global change on river system dynamics.


► Palaeoflood slackwater deposits were identified along the upper Hanjiang River. ► Peak discharge was estimated to be 65,400 m3 s- 1 using the slope-area method. ► Extraordinary flood events were dated to A.D. 200−300 using OSL method. ► Flood events are closely related to a global climatic event during A.D. 150−350. ► New data in understanding rivers’ responses to global change are presented.

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