On the Spatial Gradient of Soil Moisture-Precipitation Feedback Strength in the April 2011 Drought in the Southern Great Plains.

The southern Great Plains (SGP) experienced a record-breaking drought in 2011, in which the excessively dry conditions established quickly in spring (i.e., April) and extended into summer. A regional climate model is used (after its evaluation) to simulate this April drought and investigate how a soil moisture anomaly could affect the development of its precipitation deficit. The authors examine how the local thermodynamic structure of the overlying atmosphere contributes to soil moisture feedbacks and how these feedbacks are connected to nonlocal mechanisms. The simulations establish a zonal gradient in the (generally positive) feedback strength [i.e., a significant (negligible) precipitation increase over the eastern (western) SGP] under an SGP-wide wet soil moisture anomaly and spatially similar evapotranspiration (ET) increments. This pattern is dominated by convective precipitation and consistent with spatial gradients in parameters relevant to moist convection, including the precipitable water, the low-level instability and humidity, and the local cloud water content. All these variables are sensitive to a wet soil moisture anomaly, but precipitation responds differently to their changes in different locations. Furthermore, the impacts of the soil moisture anomaly on various large-scale atmospheric fields are related to the spatial structure of feedback strength. Additionally, the weaker feedback over the western SGP occurs in a region of relatively strong subsidence and changes little with a westward expansion of the anomaly area, whereas nonlocal soil moisture impacts-in particular, moisture advection from the west-are important for the stronger feedback over the eastern SGP. [ABSTRACT FROM AUTHOR]