SPoRT LIS Product Helpful in Deconstructing a Minor Flood Event

NASA SPoRT has developed a real-time application of the NASA Land Information System (LIS) that runs over much of the central and eastern United States. The LIS produces several products, including a suite of soil moisture products that can be used to help assess drought and flooding potential. There are four LIS soil moisture products that are made available to WFO Raleigh forecasters in AWIPS-2 and which are available online for the Southeast and for North Carolina.

A fairly significant rain event occurred across central North Carolina on 15 and 16 October 2014 as a cold front and a wave of low pressure moved across the region. Two day precipitation totals across the WFO RAH CWA (Fig. 1) indicated between 0.75 and 1.25 inches of rain fell across the western Piedmont with much more significant amounts generally ranging between 1.5 and 3.0 inches across the eastern Piedmont and Coastal Plain of North Carolina. The heaviest rain occurred across Franklin, eastern Wake, northern Johnston, and western Nash Counties.

Fig. 1. Analyzed two day two day precipitation totals across the WFO RAH CWA on 15 and 16 October 2014.

Fig. 1. Analyzed two day two day precipitation totals across the WFO RAH CWA on 15 and 16 October 2014.

One of the SPoRT-LIS fields that forecasters have found quite useful during the assessment is the one-week change in total column relative soil moisture (RSM, 0-2 m). The RSM is the ratio of the current volumetric soil moisture between the wilting and saturation points for a given soil type, with values scaling between 0% (wilting) and 100% (saturation). The one-week change product valid at 12 UTC on 14 October, just prior to the rain event, is shown in Fig. 2 with the RAH CWA outlined in red. This product indicates that much of the southern and eastern portions of the RAH CWA have experienced a relative soil moisture decrease during the previous week, while locations near the Virginia border, especially across the northern Piedmont have had a relative soil moisture increase.

Fig. 2. The one-week change in total column relative soil moisture valid at 12 UTC on 14 October 2014 with the RAH CWA outlined in red.

Fig. 2. The one-week change in total column relative soil moisture valid at 12 UTC on 14 October 2014 with the RAH CWA outlined in red.

This rainfall produced significant rises on many rivers and creeks across the northeast Piedmont and the Coastal Plain of North Carolina. Figure 3 shows the gage height on the Swift Creek at Hilliardston which had an uncharacteristic rapid response and the gage height on the Neuse River at Smithfield which exceeded flood stage.

Fig. 3. Gage heights for the Swift Creek at Hilliardston (left) and the Neuse River at Smithfield (right).

Fig. 3. Gage heights for the Swift Creek at Hilliardston (left) and the Neuse River at Smithfield (right).

It was noted that the locations that experienced the most significant rises along with some flooding where in the river basins that had a notable overlap of the one-week increase in total column relative soil moisture prior to the event and the basins which experienced the most significant rainfall as shown in the composite image in Fig. 4.

Fig. 4. Composite chart of the one-week change in total column relative soil moisture valid at 12 UTC on 14 October and the analyzed two day two day precipitation totals on 15 and 16 October 2014 along with the locations of the gages for the Swift Creek at Hilliardston and the Neuse River at Smithfield.

Fig. 4. Composite chart of the one-week change in total column relative soil moisture valid at 12 UTC on 14 October and the analyzed two day two day precipitation totals on 15 and 16 October 2014 along with the locations of the gages for the Swift Creek at Hilliardston and the Neuse River at Smithfield.

One thought on “SPoRT LIS Product Helpful in Deconstructing a Minor Flood Event

  1. Thanks for the detailed post, Raleigh! A quick comment: It would be helpful to look back at the actual total column relative soil moisture map prior to the event to determine areas that were relatively more or less moist, and how those areas overlapped with the stream gage/flooding reports. The corresponding total column relative soil moisture image at 1200 UTC 14 October can be found at: http://weather.msfc.nasa.gov/cgi-bin/basicLooper.pl?category=lis_NC&initialize=first&regex=swet_20141014_12z_nc.gif.

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