Interdecadal shifts and associated atmospheric circulation anomalies of heavy precipitation during the warm-season in the Upper Yellow River Basin over the past 40 years

Abstract

The Upper Yellow River Basin (UYRB), located at the junction of the Qinghai-Tibet Plateau, Loess Plateau, and Inner Mongolia Plateau, plays a pivotal role in regional climate dynamics, hydrological processes, and ecological stability, primarily due to its precipitation variability. This study utilizes station-based observational data alongside atmospheric reanalysis data to investigate the interdecadal variability of heavy precipitation during the warm-season from 1980 to 2020 in the UYRB. Furthermore, it provides a comparative assessment of the atmospheric circulation patterns that influenced the observed shifts in heavy precipitation across different periods. The analysis revealed pronounced interdecadal changes in warm-season total precipitation (WSTP), heavy precipitation amount (R90p), and heavy precipitation frequency (R90d) around 2003. Heavy precipitation contributes approximately 40 % to the total precipitation, while changes in heavy precipitation account for up to 81 % of the increased total precipitation in the UYRB, the light precipitation exhibit a negative contribution, and moderate precipitation shows a slight positive contribution. Additionally, the variation in the frequency of heavy precipitation contributes the most, reaching 7 mm/10a, while the intensity of precipitation is only 1.5 mm/10a. After 2003, the frequency of heavy precipitation (R90d) during the warm-season increased by 14.4 %, whereas the intensity of heavy precipitation (R90t) rose by a modest 4.3 %, indicating that the increase in R90d predominantly drives the long-term trend in WSTP over the UYRB. The key factors such as moisture transport, moisture content, instability energy, and vertical motion were compared between two distinct periods: 1980–2002 (Period1) and 2003–2020 (Period2). During P2, there was a marked intensification of anomalous easterly moisture transport and moisture convergence throughout the atmospheric column, resulting in a nearly 50 % increases in net moisture input and a rise of 2.7 % in total columnar moisture content relative to P1. Atmospheric instability exhibited a slight increase, with notable anomalous convergent upward motion detected over the source region of the Yellow River and central Gansu province, likely intensified by orographic effects. A zonally-oriented “+ - +” Silk Road-like teleconnection pattern emerged in the mid-to-upper troposphere over Eurasia since 2003, enhancing westward moisture transport from the Indian Ocean and Pacific. This shift corresponded with increased moisture availability and vertical ascent during the warm-season, which is conducive to a significant increase in heavy precipitation over the UYRB.