Response of lower Yellow River bank breachings to La Niña events since 924 CE

Abstract

The El Niño/Southern Oscillation (ENSO) is the dominant mode of inter-annual climate variability, strongly affecting summer precipitation and streamflow of large rivers. So far, no effort has been made to relate ENSO events with alluvial river stability. Based on the historical document of the lower Yellow River (LYR) and the data of previously reconstructed ENSO variability, the present study aims to establish the relation between the LYR's artificial levee breaching events (LBEs) and the ENSO events from 924 CE to 1938, and thereby reveal how river instability responds to climate change in millennial scale, for a better understanding of the coupling relation between the climate, hydrology and river channel changes. From 924 CE to 1938, there are 303 La Niña influenced years (ENSO variability < −0.5), of which 172 (56.8%) are related to the occurrence of LBE. We divided the reconstructed ENSO variability into 9 classes and calculated the LBE frequency for each class. We found that the LBE frequency is negatively correlated with class average value of ENSO variability, significant at p < 0.05. By relating the 21 major course shifting events (CSEs) of the LYR (924 CE to 1938) to the occurrence of La Niña influenced years, we found that 13 (61.9%) were influenced by La Niña. The decadal LBE frequency (Fb) and decadal average of ENSO amplitude show anti-phase variations since 1100 CE, with r = −0.356 (n = 82, p = 0.0010) after a linear detrending treatment. Through the control on summer rainfall and therefore on floods in the Yellow River, La Niña events influence the occurrence of the LBEs and CSEs in the LYR.