Spatial-temporal evolution of meteorological and groundwater droughts and their relationship in the North China Plain

Understanding the propagation dynamics from meteorological droughts to groundwater droughts and their spatial–temporal evolution is essential for monitoring and assessing groundwater drought risk. In this study, the Standardized Precipitation and Evapotranspiration Index (SPEI) and Gravity Recovery and Climate Experiment (GRACE) Groundwater Drought Index (GDI) were used for assessing meteorological and groundwater droughts, respectively, in the North China Plain (NCP). The Directed Information Transfer Index (DITI) was used to identify the propagation from meteorological droughts to groundwater droughts. The verification results indicated good reliability of GRACE data for assessing drought events in the NCP. From the view of temporal variation, the SPEI-1 was first decreased and then increased, and the minimum value was in 2011. The GDI was first increased and then decreased, and the maximum was in 2008. In terms of spatial distribution, the SPEI-1 significantly decreased in the central part of the NCP before 2011. The 2011–2020 period revealed an increasing trend in SPEI-1 in many parts of the NCP. According to the GDI results, an increasing trend was observed in the central and western parts of the NCP before 2008, and many parts of the study region revealed a decreasing trend in GDI during the 2008–2020 period. The propagation time of SPEI-1 to GDI was long in spring and winter and short in summer. The maximum DITI values ranged from 0.4 to 0.9 and the most spread time was about 18 to 24 months in the northern and southern parts of Hebei and the northern part of Henan province, covering 36.40% of the total surface area of the NCP. Regarding the drought sensitivity and propagation rate, the dominated distribution was in a pattern of high in the northern and low in southern parts of the NCP, with the rates of 38.44% and 34.17%, respectively.