image Credit: Drought.gov

Soil moisture is defined as the total amount of water that can be found in the space between soil particles and is often measured as volumetric water content (VWC), which represents the percentage of water volume within a given soil volume (Strangeways 2003). This moisture level plays a crucial role in determining how much water can infiltrate the soil, run off into rivers, or return to the atmosphere through evaporation and plant transpiration. Once water has infiltrated the soil, it is either used by plant roots, recharges groundwater, or travels back to the surface and evaporates (Hillel 1998). In turn, several factors such as soil type, organic matter, precipitation, and temperature influence the amount of soil moisture present. Soil moisture is often categorized by depth, with the top layer called surface soil moisture and measuring 0-5cm depth of the soil. Soil from 0-100cm depth is called rootzone soil moisture while measurements from the surface to bedrock (0-bedrock cm) are called profile soil moisture (Reichle et al., 2025).

Soil moisture measurements have a wide array of applications, including:

  • Monitoring for drought
  • Assessing landslide risk
  • Weather forecasting
  • Predicting crop yields
  • Managing irrigation
  • Monitoring wildfire risk

For this study, I assess rootzone soil moisture for the month of November. I selected a single month to limit the amount of data and workload for this project; however, the tool created could be used for any time period. November was selected due to the month’s importance for forecasting agricultural conditions (Osenga, 2021).

References

  • Hillel, D., 1998, Environmental Soil Physics: San Diego, California, Academic Press, 771 p.
  • Reichle, R.H., G. De Lannoy, R.D. Koster, W.T. Crow, J.S. Kimball, Q. Liu, and M. Bechtold. 2025. SMAP L4 Global 3-hourly 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data, Version 8. SPL4SMGP. Boulder, Colorado, USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. https://doi.org/10.5067/T5RUATAQREF8.
  • Strangeways, I.C., 2003, Soil moisture and groundwater, in Measuring the Natural Environment: Cambridge, Cambridge University Press, p. 178–222, https://doi.org/10.1017/CBO9781139087254.009
  • Osenga, E., 2021, Year-end soil moisture update: Aspen Global Change Institute, December 21, available at https://www.agci.org/blog/year-end-soil-moisture-update (last accessed April 20, 2026).
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