Terrestrial ecological drought dynamics and its response to atmospheric circulation factors in the North China Plain

Ecological drought is a natural disaster caused by the shortage of water supply, which can lead to many problems such as the reduction of vegetation greenness, shrinkage of water area, and destruction of biological habitats. In view of the increasingly serious problem of ecological drought in the North China Plain (NCP), the remotely sensed vegetation health index (VHI) was adopted to characterize the ecological drought phenomenon. In this study, the modified Mann-Kendall (MMK) and Hurst index methods were used to analyze the spatio-temporal coupling dynamic variation of ecological drought. Subsequently, the Breaks for Additive Seasons and Trend (BFAST) algorithm was employed to explore the segmented trend characteristics and mutation point types. Furthermore, the cross wavelet transform and multiple wavelet coherence were applied to reveal the mutual effect of atmospheric circulation factors on ecological drought. The results indicated that: (1) the ecological drought showed an overall alleviation trend from 1982 to 2020 in the NCP; (2) the trend type of VHI was interrupted increase in Tianjin (TJ) and Hebei (HB) with a mitigated drought trend, and was decrease to increase in Beijing (BJ) and Henan (HN) with a slight increase and then significant decrease drought trend, and all the mutation points occurred before 2000 during the study period; (3) the most severe ecological drought occurred in winter with a minimal VHI of 0.519, and the least severe ecological drought appeared in summer with a maximal VHI of 0.581; and (4) the combination of atmospheric circulation factors, North Atlantic Oscillation (NAO)-Atlantic Multidecadal Oscillation (AMO)-Arctic Oscillation (AO), had the strongest driving effect on ecological drought, which can be adopted as input variables of drought pre-warning mechanism for improving the accuracy of drought prediction.