Modulation of centennial-scale hydroclimate variations in the middle Yangtze River Valley by the East Asian-Pacific pattern and ENSO over the past two millennia

Abstract Many studies have shown that the northward (southward) displacement of the East Asian westerly jet (EAWJ) drastically reduces (increases) summer rainfall in the Yangtze River valley (YRV). However, the effect of the jet’s intensity on interannual variation in summer rainfall has not been systematically studied. The present study investigates the effect of the EAWJ’s intensity on this interannual variation and analyzes the mechanism by which this process occurs. In early summer, the EAWJ consists of two branches: one located over northern continental East Asia [western branch (EAWJWB)] and one extending from southern China to the northern Pacific [eastern branch (EAWJEB)]. The former merges into the latter over the Yellow Sea. A stronger EAWJEB leads to increased rainfall in the YRV, while the EAWJWB does not significantly affect rainfall in the YRV. The faster EAWJEB directly strengthens midtropospheric warm advection over the YRV because the corresponding changes in the meridional wind and horizontal temperature gradient are insignificant. The strengthened warm advection increases rainfall in the YRV by accelerating both adiabatic ascent and the ascent associated with diabatic heating primarily generated by convection. In midsummer, the EAWJ has no branches and is located over the midlatitudes of Asia. The strengthening of the EAWJ reduces rainfall in the YRV in midsummer through the Pacific–Japan (PJ) pattern. As the EAWJ strengthens, the PJ pattern turns to its positive phase. This results in the deceleration of the midtropospheric westerly wind and a reduction in the meridional temperature contrast, which weakens midtropospheric warm advection. The weakened warm advection in turn reduces rainfall in the YRV, following the process outlined for early summer.

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Holocene Environmental Archaeology of the Yangtze River Valley in China: A Review

Land ◽

10.3390/land10030302 ◽

2021 ◽

Vol 10 (3) ◽

pp. 302

Author(s):

Li Wu ◽

Shuguang Lu ◽

Cheng Zhu ◽

Chunmei Ma ◽

Xiaoling Sun ◽

...

Keyword(s):

Climate Change ◽

Yangtze River ◽

Large Scale ◽

Yangtze River Valley ◽

River Valley ◽

Interactive Effects ◽

Environmental Archaeology ◽

The Yangtze River ◽

The Past ◽

Neolithic Cultures

The Yangtze River Valley is an important economic region and one of the cradles of human civilization. It is also the site of frequent floods, droughts, and other natural disasters. Conducting Holocene environmental archaeology research in this region is of great importance when studying the evolution of the relationship between humans and the environment and the interactive effects humans had on the environment from 10.0 to 3.0 ka BP, for which no written records exist. This review provides a comprehensive summary of materials that have been published over the past several decades concerning Holocene environmental archaeology in the Yangtze River Valley, to further understand large-scale regional Holocene environmental and cultural interaction within this area. The results show that: 1) in recent years, Holocene envi-ronmental archaeology research in the Yangtze River Valley has primarily taken paleoflood and sea-level change stratigraphical events to be the foundational threads for study. This began with research on the spatiotemporal distribution of archaeological sites, typical archaeological site stratigraphy, and research on background features concerning environmental evolution recorded by the regional natural sedimentary strata. 2) Significant progress has been made at the upper, middle, and lower reaches of the Yangtze River, indicating that Holocene environmental ar-chaeology research along the Yangtze River Valley is deepening and broadening. 3) Dramatic changes to Neolithic cultures that occurred approximately 4.0 ka BP were influenced by climate change and associated consequences, although the impacts differed on the various Neolithic cultures in the Yangtze River Valley. Local topography, regional climate, and varying survival strategies may have contributed to these differences. 4) Newly-published research pays particular attention to the sedimentary records of the past with resolutions as high as one year to several months, the degree to which humans altered the quality of their natural environment, and human adjustments to settlement and subsistence practices during periods of Holocene climate change. The application of technologies such as remote sensing, geographic information systems (GIS), and molecular biological analysis are also gradually being extended into the research field of Holocene environmental archaeology in the Yangtze River Valley.

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New Predictors and a Statistical Forecast Model for Mei-Yu Onset Date in the Middle and Lower Reaches of the Yangtze River Valley

Weather and Forecasting ◽

10.1175/waf-d-13-00109.1 ◽

2014 ◽

Vol 29 (3) ◽

pp. 654-665 ◽

Cited By ~ 4

Author(s):

Yijia Hu ◽

Yimin Zhu ◽

Zhong Zhong ◽

Yao Ha

Keyword(s):

Yangtze River ◽

Asian Summer Monsoon ◽

East Asian ◽

Forecast Model ◽

Yangtze River Valley ◽

River Valley ◽

Onset Date ◽

The Yangtze River ◽

Tropical Ocean ◽

Preceding Winter

Abstract The prediction of mei-yu onset date (MOD) in the middle and lower reaches of the Yangtze River valley (MLYRV) is an important and challenging task for those making seasonal climate predictions in China. In this paper, the atmospheric and oceanic conditions in the preceding winter and spring related to MOD are analyzed. It is found that the MOD is associated with the intensity of the Ural high and the East Asian trough in high latitudes, with the intensity of the upper-level westerly jet in middle latitudes, and with the contrast of land–sea temperature and pressure in the preceding winter and spring, which are proxies for the intensity of the East Asian winter monsoon (EAWM). It is suggested that the intensity of the EAWM is the most crucial factor affecting the MOD. Years with an early MOD usually correspond to strong EAWMs in the preceding winter, and vice versa. The EAWM can affect the MOD by influencing the East Asian summer monsoon (EASM) through tropical ocean–atmosphere and tropical–extratropical interactions. Based on the above analysis, a physics-based statistical forecast model is established using multivariable linear regression techniques. The hindcast of MOD during the 13 yr from 1998 to 2010 is carried out to evaluate the performance of this forecast model. The MOD can be predicted successfully in 8 out of the 13 yr. The forecast model predicts the MOD in the years with strong mei-yu intensity more accurately than in those with weak mei-yu intensity, especially for cases of extreme flooding. This is useful in the prevention of flooding disasters.

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The influence of wind and land evapotranspiration on the variability of moisture sources and precipitation of the Yangtze River Valley

10.5194/hess-2018-629 ◽

2019 ◽

Author(s):

Astrid Fremme ◽

Harald Sodemann

Keyword(s):

Yangtze River ◽

Asian Monsoon ◽

East Asian Monsoon ◽

East Asian ◽

Precipitation Variability ◽

Yangtze River Valley ◽

River Valley ◽

The Yangtze River ◽

Moisture Source ◽

Moisture Sources

Abstract. The Yangtze River Valley (YRV) experiences large intraseasonal and interannual precipitation variability, which is mainly due to East Asian monsoon influence. The East Asian monsoon is caused by interaction of many processes in the coupled land-atmosphere-ocean system. To better understand YRV precipitation variability in this complex system, we have studied the precipitation moisture sources and their connection to YRV precipitation. We obtained the moisture sources by using the ECMWF's ERA Interim reanalysis data set, the FLEXible PARTicle dispersion model (FLEXPART) and the WaterSip moisture source diagnostic. The variability of moisture sources reflects the variability of YRV precipitation. Intraseasonal variations of moisture sources include a shift of the most important source regions as the monsoon progresses. Interannual variability of the moisture sources shows that sources which are less important climatologically are closely connected to variations of the driest and wettest years. Our results show that land directly contributes 58 % of moisture for YRV precipitation during 1980–2016, whereas the ocean contributes 42 % in direct transport. While the importance of the ocean as a moisture source is often emphasized, our results underscore the importance of the process of continental recycling and the role of land moisture sources.

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