Soil moisture mapping of drought in Texas

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Sullivan, Johnny
Maidment, David R.

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Center for Research in Water Resources, University of Texas at Austin



Texas experienced in 2011 one of the worst droughts on record. To better understand and plan for its effects, this project aimed to create a map, available online and updated in real-time, showing the extent of drought in the state of Texas based on soil moisture content information. This was to be accomplished through a combination of the available water storage data provided by the USDA Soil Survey Geographic Database (SSURGO) and the continuously updated current soil moisture data made available by NLDAS, the North American Land Data Assimilation System. The SSURGO dataset is defined at a detailed county mapping scale, while the NLDAS model operates on a climate-level scale of 1/8 degree polygons, necessitating consideration of the appropriate scale at which these two datasets should be joined. The combination of these two datasets resulted in a value of current moisture storage in which the percentage of moisture was defined by NLDAS, while the upper and lower bounds of the moisture levels were defined by SSURGO. It was decided, however, that current water storage is most easily understood on a percentage basis, so a soil wetness index was defined and it was upon this metric that the soil moisture map was based. The analysis began with a focus on Travis County but was then expanded to the remainder of the state of Texas. The soil parameters for each NLDAS grid point were acquired, and an ArcGIS geoprocessing model was created to calculate and display the average soil wetness index for each county across the state. Finally, a 33-year record of NLDAS soil moisture data was obtained, and the groundwork was laid to employ this long-term dataset in calculating the statistical significance of current soil moisture data.

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