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HOME > Monitoring & Data > U.S. Soil Moisture Monitoring > Explanation
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About the dataset (Fan & van den Dool, 2004 JGR)


Soil moisture is estimated by a one-layer hydrological model (Huang et al., 1996; van den Dool et al, 2003). The model takes observed precipitation and temperature and calculates soil moisture, evaporation and runoff. The potential evaporation is estimated from observed temperature.

Model parameters are constant spatially (tuned based on Oklahoma observed runoff data).

Tuning the model to runoff of serveal small river basins in eastern Oklahoma resulted in a maximum holding capacity of 760mm of water. Along with a common porosity of 0.47 this implies a soil column of 1.6 meter.

The precipitation and temperature are monthly data over the globe from CPC PRECipitation REConstruction over Land (Chen, M., P. Xie, J. E. Janowiak and P. A. Arkin, 2002: Global land precipitation: A 50-yr monthly analysis based on gauge observations. J. Hydrometeor., 3, 249-266) & CPC Global Land Surface Air Temperature Analysis (Fan, Y. & H. van den Dool, JGR 2008). The climatology is calculated based 1991-2020 data. The soil moisture in the current month will be re-calculated with monthly data on the 8th of next month.

What's next:

The CPC PRECipitation REConstruction over Land will undergo the the following improvements in the near future by Chen et al:

1) orographic adjustment/enhancement
2) dealing with inhomogeneity resulting from changes in number of gauges over time.

Soil moisture calculations will be repeated when such improvements are implemented.

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Page last modified: August 22, 2002
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