Assessing Spatio-Temporal Patterns and Statistical Associations of Meteorological and Agricultural Droughts in Winter Wheat Using Multi-Source Data

Characterizing the spatiotemporal differences between meteorological and agricultural drought is important for drought monitoring and risk management in major grain-producing regions. However, coordinated assessment of meteorological anomalies and crop moisture responses using multi-source data remains challenging. In this study, an integrated multi-source framework was developed to jointly characterize meteorological and agricultural drought in winter wheat across six selected growing seasons in Henan Province, China. The standardized precipitation index (SPI) and vegetation water index (VWI) were used to characterize meteorological and agricultural drought, respectively. Furthermore, standard deviational ellipse analysis and center-based spatial statistics were used to characterize drought distribution, orientation, and spatial migration, while Pearson correlation analysis was used to examine statistical associations among SPI-defined drought, VWI-defined drought, and effective irrigated area. Across the selected study periods, meteorological and agricultural drought showed distinct temporal and spatial patterns. In addition, the SPI–VWI association varied with drought severity: light drought showed the strongest positive association (r = 0.64), moderate drought showed a weak negative association (r = −0.20), and severe drought showed a moderate positive association (r = 0.57). The association between total SPI- and VWI-defined drought areas was weak (r = −0.07). At the common 1-km analysis scale, VWI-defined agricultural drought maintained a more stable spatial center and major-axis orientation than SPI-defined meteorological drought, while the difference in ellipse extent was more pronounced in the earlier study periods and narrowed markedly in the later periods. Effective irrigated area showed an exploratory negative association with total VWI-defined agricultural drought area (r = −0.72, p = 0.11; n = 6); although the association did not reach conventional statistical significance, its direction identifies irrigation conditions as relevant contextual information when interpreting variations in agricultural drought. The integrated framework provides a complementary basis for jointly assessing meteorological stress and crop moisture conditions and may support drought-risk assessment and irrigation management in major winter wheat-producing regions.