Understanding the mechanism underlying the propagation from meteorological drought to agricultural drought is of utmost significance for the development of effective drought management strategies and early warning systems. In this study, we employed three hybrid drought indicators – namely, the Vegetation Drought Response Index (VegDRI), GRACE Root Zone Soil Moisture Percentile (SMI), and Evaporative Demand Drought Index (EDDI), developed by the U.S. National Integrated Drought Information System. Through the application of wavelet coherence and cross wavelet transform analysis in the time-frequency domain, we explored the interconnections between meteorological drought, assessed using the standardized precipitation index (SPI), and agricultural drought. Our investigation was carried out within the California and Mississippi watersheds in the United States, which are characterized by diverse agro-climatic conditions and cropping systems. To unravel the propagation process, we evaluated the SPI across various temporal scales, pinpointing the 14-day scale as the most informative. Our analyses unveiled that soil moisture exhibited the swiftest response to anomalies in rainfall, with a lag of 41 days in California and 59 days in Mississippi. Subsequently, VegDRI indicated a lag of 137 days in California and 75 days in Mississippi, indicating a sequential response to rainfall anomalies. Lastly, EDDI mirrored rainfall anomalies with a lag of 143 days in California and 139 days in Mississippi, representing the slowest response to rainfall anomalies among the drought indicators. Irrigation (as a proxy for anthropogenic activities) could delay the propagation time by around two months. Employing wavelet technique and spatial clustering, we scrutinized variations in the drought propagation process concerning temporal dynamics, seasonal influences, geographical locations, and management practices such as irrigation. By shedding light on the intricate spatiotemporal aspects of the drought propagation process, this study contributes to the understanding of drought dynamics and supports the development of targeted drought management strategies.

Cross wavelet transform,Drought propagation,Irrigation,Spatial clustering,Meteorological drought,Agricultural drought