Dynamics of groundwater-land surface response times as a dryland flash drought diagnosis

The delayed response time of groundwater storage and surface soil moisture dynamics, indicating how quickly anomalies propagate from the surface to the aquifer, varies across climate regimes. Understanding its spatiotemporal variability can support diagnosing flash drought, yet it remains underexplored. Here, we examine global relationships between groundwater-land surface response time and flash drought under land-atmosphere interactions via a dynamic exponential filter. We find that longer groundwater-land surface response times likely occur with frequent flash droughts in drylands. However, groundwater-land surface response time indicates higher immediate bidirectional sensitivities with flash drought indicator and timing in wetter seasons, suggesting its suitability for early-stage flash drought prediction. These are mainly driven by land-atmosphere interplays, where the combined evapotranspiration-runoff deficit in drylands rapidly prolongs the response time and reduces the sensitivity to flash drought characteristics. These insights highlight the potential of groundwater-land surface response time for flash drought diagnosis, offering a practical pathway for improving early warning capabilities.