Soil characteristics in North Carolina (follow-up to WFO RAH post)

The previous blog post made by the NWS forecast office at Raleigh, NC (WFO RAH) illustrated the decrease in LIS total column relative soil moisture over North Carolina (NC) associated with the recent lack of rainfall through 1 September.  Despite receiving some nominal precipitation up to 0.50″ during the previous week, portions of eastern NC experienced the greatest amount of soil drying compared to central NC where practically no rain fell.

This response in the Noah land surface model within the real-time SPoRT-LIS is related to the disparate soil composition across NC as seen in Figure 1.  The soils consist of mostly sand or sandy loam composition across eastern NC compared to silty loam in central NC.  The movement of water in lower porosity, sandy soils is dominated by capillary action (upward movement of water against gravity) and thus readily release its water at higher soil moisture values.  Meanwhile, higher porosity soils (i.e., clay/silt with numerous smaller pores) retain water for longer time periods and tend to dry out more slowly at higher values of soil moisture (google “water retention curve” for more details).  Thus, despite the modest rainfall over the sandy soils of eastern NC, the soil actually dried out faster than over central NC where less rainfall was observed.

soilType_nc

Figure 1. Soil texture classifications used in the SPoRT-LIS runs of the Noah land surface model, centered over North Carolina.

3 thoughts on “Soil characteristics in North Carolina (follow-up to WFO RAH post)

  1. Thanks for replying about this Jon. I think this issue that RAH brought up is one of the most useful aspects of the LIS soil moisture for drought analysis. Rainfall that occurs across a region will not be “treated” the same way by the near-surface soils and those differing soil characteristics can have big impacts on agriculture or basin hydrology in the region. A weekly one inch rainfall on top of silt-loam soils will indeed have different soil moisture outcomes than a one inch rainfall on top of sandy soils

  2. N: National Centers for Environmental Prediction (NCEP)
    O: Oregon State University (Dept of Atmospheric Sciences)
    A: Air Force (both AFWA and AFRL – formerly AFGL, PL)
    H: Hydrology Lab – NWS (formerly Office of Hydrology – OH)
    (Taken from NOAH User Guide)

    The community NOAH LSM was developed beginning in 1993 through a collaboration of investigators from public and private institutions, spearheaded by the National Centers for Environmental Prediction (Chen et al. 1996; Koren et al. 1999). NOAH is a stand-alone, 1-D column model which can be executed in either coupled or uncoupled mode. The model applies finite-difference spatial discretization methods and a Crank-Nicholson time-integration scheme to numerically integrate the governing equations of the physical processes of the soil-vegetation-snowpack medium. NOAH has been used operationally in NCEP models since 1996, and it continues to benefit from a steady progression of improvements.
    (Taken from description on NASA/GSFC site)

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