Dominant patterns of dryness/wetness variability in the Huang-Huai-Hai River Basin and its relationship with multiscale climate oscillations

The understanding of dryness/wetness variability and its causes is vital for better water resources management, especially in precipitation deficit regions. This study assesses the behavior and potential risk of summer meteorological dryness/wetness, characterized by the Standardized Precipitation Evapotranspiration Index (SPEI), in the semiarid Huang-Huai-Hai (HHH) River Basin in northern China using Precipitation (P) and Potential Evapotranspiration (ET0) data of 186 stations during 1960-2017. The dominant patterns of dryness/wetness variability in the HHH river basin and the connections with atmospheric circulation and multiscale climate oscillations are also detected. The results show that (1) a general wetting trend can be detected in the HHH during summer using the rank-based nonparametric Mann-Kendall test, which is largely related to the increase in summer P and decrease in summer ET0, and the trends in summer SPEI based dryness/wetness are more sensitive to the changes in ET0 than in P; (2) the patterns of dryness/wetness variability over the HHH river basin can be dominantly represented by three leading Empirical Orthogonal Function (EOF) modes, which are strongly influenced by large-scale atmospheric circulations, such as the excessive (insufficient) precipitation, upward (downward) vertical motion and moisture convergence (divergence); and (3) the multiscale climate modes have significant effects on the dryness/wetness variability, which confirms the interactions between multiple lowfrequency oscillations and the meteorological processes in the HHH river basin. The results of this study will be beneficial for water resources management, drought/flood forecast, and preparations for potential drought/ flood hazards in the HHH River Basin and will also be a valuable reference for other arid and semiarid areas.

Automated summary

The study reveals a general wetting trend in the HHH River Basin during summer, driven by increased precipitation and decreased evapotranspiration. The patterns of dryness/wetness variability are dominantly represented by three leading Empirical Orthogonal Function (EOF) modes, strongly influenced by large-scale atmospheric circulations. Multiscale climate modes have significant effects on the dryness/wetness variability, indicating interactions between low-frequency oscillations and meteorological processes.