Droughts are dominated by anomalous circulation not anomalous atmospheric moisture content

SeungUk Kim , Diego G. Miralles, Francina Dominguez

Agricultural drought is a sustained soil moisture deficit caused by reduced net moisture flux to the land surface. We show that agricultural droughts can occur when the atmosphere is anomalously wet, challenging the assumption that surface drying reflects atmospheric moisture deficits. Precipitation declines during drought even under increased atmospheric moisture, indicating low precipitation efficiency: subsidence and reduced relative humidity suppress condensation, while enhanced moisture divergence exports water from the column. Moisture budget analysis reveals that divergence driven by anomalous circulation accounts for most of the drying, while advection by anomalous winds governs the spatial pattern of total column water. In contrast, advection of anomalous moisture largely counteracts drying. Droughts are thus dominated by anomalous winds that export water, rather than by limited moisture supply.