Land Surface Monitoring and Prediction
CPC Leaky Bucket Model
The objective of this webpage is to provide support for the National Integrated Drought Information System (NIDIS).
Soil moisture is estimated by a one-layer hydrological model (Huang et al., 1996, van den Dool et al., 2003, Fan & Van den Dool 2004, Zeng et al., 2020). The model takes as forcing 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 and tuned to reproduce runoff of several small river basins in eastern Oklahoma. This resulted in a maximum holding capacity of 760mm (or 29.9 inches) of water. Along with a common porosity of 0.47 this implies a soil column of 1.6 meter (=5.25 ft).
At the present time, this hydrological model runs in two different configurations:
(1) Daily and monthly updates over 344 US Climate Divisions.
The observed precipitation and temperature are monthly data over 344 Climate Divisions from NCDC (1895-present). The monthly data update is usually available on the 5th of current month. The daily soil moisture data set in the current month is calculated with real time daily precipitation and temperature from CPC in-house products with 1 day lag.
(2) Daily and monthly update over the global (0.5x0.5 degree resolution) domain.
The daily and monthly global soil moisture data set (Fan & Van den Dool, 2004 JGR) is calculated with observed CPC Unified global precipitation analysis (Chen et al 2008 JGR) and CPC global surface air temperature analysis (Fan & Van den Dool, 2008 JGR, Wei Shi 2012). The monthly update is usually available around 5th of current month.
NOTE1: Please be aware of the problems caused by using real time station data in calculating soil moisture for the current month. Daily station precipitation tends to be heavier compared to climate division data. Also, when using GrADS to plot station data, we implicitly use Cressman analysis. It may create some unrealistic values, especially in areas with big gradients or in the boundary area.
NOTE2: In many displays we show "anomalies" and "percentiles". Anomalies are defined as deviations from the 1991-2020 daily or monthly climatology. Percentiles are against 1895 (344 US Climate Divisions) or 1979 (global domain) to most recent soil moisture records.
References:
If you have any questions concerning any of the products provided here, please contact Yun.Fan@noaa.gov.
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