Hydrometeorology of the catastrophic Blanco river flood in South Texas, May 2015

Abstract Study region This study was carried out along the Blanco River in south-central Texas which drains approximately 1100 km2. Study focus Unprecedented rainfall across the state of Texas in May 2015 produced flooding that claimed at least 24 lives across the state. The most devastating single event over this period occurred on 23–24 May along the Blanco River, where a fast moving floodwave resulted in eleven fatalities in the town of Wimberley. The storm event resulted in the flood of record at the USGS gauge in Wimberley which has collected data since the 1920s. New hydrological insights Meteorological observations, high-resolution rainfall estimates, and physics-based distributed hydrological modeling provide the opportunity to examine the hydrometeorological mechanisms accompanying the extreme storm and subsequent flood. Additionally, transpositions of the radar rain fields forced through the hydrologic model allow for analysis of the effect of position of the centroid of the storm relative to the catchment on floodwave propagation. Two major controls on the flood response are identified and analyzed: the position of heavy storm cells over the headwaters with subsequent slow movement downstream and the extremely moist antecedent conditions prior to the onset of the event.

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