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.