Regime shift of the hydroclimate–vegetation system in the Yellow River Delta of China from 1982 through 2015

The Yellow River Delta (YRD) has been experiencing substantial climatic, hydrological, and anthropogenic stresses, and a sound understanding of the regime shift in its hydroclimate–vegetation system is of fundamental importance for maintaining the health and stability of its regional ecosystems. This study constructs and analyzes a 34-year-dataset (1982–2015) of hydro–climatic variables and satellite-based Normalized Difference Vegetation Index (NDVI) in the YRD. A seasonal-trend decomposition technique based on loess (STL), and a structural change analysis were coupled to detect regime shifts of regional hydroclimate and vegetation in the YRD from 1982 through to 2015. During this period the YRD exhibited a significant warmer–drier–greening trend and experienced four regime shifts of its hydroclimate–vegetation system, with the four shift periods roughly centered in 1989, 1998, 2004, and 2012. Partial correlation analysis revealed that temperature was the dominant factor promoting vegetative growth in spring and autumn (all P NDVI-TEM greater than 0.65), and streamflow impacted the NDVI mainly in summer. Temperature and precipitation were the dominant controls of vegetative growth during the growing season prior to 2002, and thereafter precipitation and streamflow alternately became the main moisture-influencing factors of vegetative growth. Streamflow played an important complementary role on vegetative growth, particularly in near riverine areas when drought exceeds a certain threshold. Additionally, climate shifts determined the changing trend of NDVI across the region, while the effect of land use change is localized and predominant in the northeastern part of the study region. These findings offer an insight into appropriate water regulation of the Yellow River and on climatic adaptation within the YRD.