Evaluating the Spatiotemporal Evolution and Divergent Drivers of Agricultural Drought in the North China Plain Using SSMI

The North China Plain is a core grain-producing region in China. Under the dual pressures of global warming and intensifying human activities, frequent agricultural droughts pose a serious threat to regional food security and sustainable agricultural development. Based on ERA5-Land root-zone soil-moisture data (1982–2022), this study constructed the Standardized Soil Moisture Index (SSMI) and applied an MMK trend test, Partial Wavelet Coherence (PWC), and sub-regional Pearson correlation to investigate drought evolution and driving mechanisms. Groundwater-level and effective-irrigated-area datasets were further incorporated to complement soil-moisture-based analysis and investigate the anthropogenic drivers behind drought variations. The results show that: (1) The regional-average SSMI showed a significant decreasing trend at a rate of −0.013 decade−1 (p < 0.001), indicating the intensification of agricultural drought. Meanwhile, the SPEI presented a non-significant increasing trend of 0.145 × 10−2 decade−1 (p < 0.001), revealing the existence of hysteresis between the two drought types. Spring suffered the most severe drought, while drought is alleviated by precipitation replenishment in summer, which highlighted the association between seasonal differences and regional climatic characteristics. (2) Groundwater level (GW) is identified as the dominant explanatory factor for agricultural drought (POSC = 70.53%, AWC = 0.93), far exceeding precipitation (16.66%) and evapotranspiration (8.71%), which underscores the pivotal role of groundwater in regulating soil moisture. (3) The driving mechanisms of agricultural drought exhibit remarkable north–south differentiation: southern sub-regions are predominantly driven by meteorological factors, whereas northern sub-regions are closely associated with intensive groundwater irrigation. Anthropogenic groundwater over-extraction shows strong statistical associations with agricultural drought variability. Future work should combine groundwater dynamics, irrigation and crop phenology. These findings support refined drought early-warning and region-tailored mitigation for the North China Plain.