About the dataset (Fan & van den Dool, 2004 JGR)

Model:

Soil moisture and snowpack are estimated by a one-layer hydrological model (Huang et al., 1996; van den Dool et al., 2003; Zeng et al., 2020). The model takes observed precipitation and temperature and calculates soil moisture, evaporation, runoff and snowpack. 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.

Forcing Datasets:

The precipitation and temperature (0.5x0.5 degree resolution) are daily observed data over the globe from CPC Daily Unified Precipitation Analysis 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 Daily Global Land Surface Air Temperature Analysis (Wei Shi 2012, Fan Y. & H. van den Dool, JGR 2008). The climatology is calculated based 1981-2010 data.