J30.5 The Role of the Edwards Plateau and Balcones Escarpment in Texas in Modulating August Precipitation Distribution: The Importance of Soil Type Contrast

Tuesday, 9 January 2018: 2:30 PM
Room 18A (ACC) (Austin, Texas)
Xiao-Ming Hu, Univ. of Oklahoma, Norman, OK; and M. Xue and R. McPherson

The Balcones Escarpment in central Texas is a sloped region between the Edwards Plateau and the coastal plain. The metropolitan areas located along the Balcones Escarpment (e.g., San Antonio, Austin, and Dallas-Fort Worth) are prone to heavy rain and devastating flood events. While the associated hydrological issues of the Balcones Escarpment have been extensively studied, the meteorological impacts of the Edwards Plateau and Balcones Escarpmentare not well understood. The indeterminate impacts of the thermal and dynamic effects of the Edwards Plateau on August climatological precipitation are investigated in this study using the multi-sensor Stage IV precipitation data, high-resolution dynamic downscaling, and short-term sensitivity simulations. Analysis results indicate that the total August precipitation east of the Balcones Escarpment is suppressed and precipitation over the eastern part of the Edwards Plateau is enhanced. Locally initiated moist convection in the afternoon contributes most to the total precipitation during August in the region. The dynamic downscaling output captures the spatial pattern of afternoon precipitation, which is well aligned with the simulated upward motions. The clay-based soil types that dominate the Edwards Plateau have great potential to retain soil moisture and limit latent heat fluxes, consequently leading to higher sensible heat flux than over the plain to the east. As a result, vertical motion is induced, triggering the afternoon moist convection over the Edwards Plateau under favorable conditions. In comparison, the sloping terrain plays a smaller role in triggering the convection. Short-term sensitivity simulations for a clear day confirm and further prove such a diagnosis.
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