Moisture Transport versus Precipitation Change in Sub-Basins of the Yangtze River Basin

Jihua Chen,Yingfei Wang,Yingping Huang,Ying Li,Biao Xiong,Shuangshuang Zhou,Xi Yuan

doi:10.3390/w14040622

Abstract

The Yangtze River Basin (YRB) exhibits great climate heterogeneity, from high-elevated source areas dominated by westerlies to downstream wetlands sensitive to monsoon flows. However, the atmospheric hydrological cycle and associated precipitation changes are rarely being synthetically studied in different sub-basins of the YRB, which are particularly important since floods in the main stream largely result from the superposition of precipitation-runoff peaks from different sub-basins. By dividing the entire YRB into 12 sub-basins, this study presents a preliminary analysis of precipitation features and the associated moisture transport characteristics at the sub-basin scale during 1961–2015. Results suggest that the peak month of precipitation in the northwest sub-basins (July) is one month later than that in the southeast sub-basins (June). The highest total column water vapor (TCWV) contributes to the peak precipitation in July in the northwest sub-basins, while the peak precipitation in June in the southeast sub-basins is more relative to the interaction among multi-circulations (featured by relatively high westerly moisture transport and relatively low south monsoon contribution in the progression process of monsoon precipitation belt). The south monsoon moisture during summer seldom reaches the source region basin (SRB), the Jinshajiang River Basin (JRB), and the Mintuojiang River Basin (MTB). During 1961–2015, the precipitation mainly exhibits an “increase–decrease–increase” pattern from the source region to downstream; however, it is unlikely that this pattern is forced by the TCWV and zonal/meridional moisture transport. In addition, the moisture transport anomalies between wet and dry years are also defined in the 12 sub-basins, and these anomalies are characterized by significantly different moisture transport patterns.

Highlights

The Yangtze River Basin (YRB) spans three distinct terrain levels of China, originating from the high-altitude Tibetan Plateau, across the Hengduan Mountains, the Yunnan– Guizhou Plateau, the Sichuan Basin, and the Southern Yangtze River Hills, to the fertile wetlands of the Middle-Lower Yangtze River Plain (Figure 1)
Of more concern is the heavy precipitation over the YRB, when the atmospheric circulation pattern is characterized by a northwestward extension of WPSH and a southward shift of the East Asian westerly jet (EAJ)
The most visible discrepancies among the three datasets are mainly located in the southeastern YRB, where the values of total column water vapor (TCWV) and moisture flux are relatively higher in ERA5 and MERRA-2 than that in JRA-55

Summary

Introduction

The Yangtze River Basin (YRB) spans three distinct terrain levels of China, originating from the high-altitude Tibetan Plateau, across the Hengduan Mountains, the Yunnan– Guizhou Plateau, the Sichuan Basin, and the Southern Yangtze River Hills, to the fertile wetlands of the Middle-Lower Yangtze River Plain (Figure 1). Of more concern is the heavy precipitation over the YRB, when the atmospheric circulation pattern is characterized by a northwestward extension of WPSH and a southward shift of the East Asian westerly jet (EAJ). These produce a mass of low-latitude oceanic moisture transport to the YRB; by contrast, in dry years, a weak WPSH and a northward displacement of EAJ are usually accompanied by the moisture convergence zone displaces to the north of the YRB [12,28,35,36,37]. The invasion of north cold air mass and the largely variational westerlies may promote the formation of a convergence zone over the YRB by blocking the northward movement of monsoon flows [38,39,40]

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Discussion

Conclusion