Land Surface Parameters

The basic soils information used in GLDAS was derived from the global soils dataset of Reynolds, Jackson, and Rawls [1999, WRR2000], which is available online here. That dataset includes fractions of sand, silt, and clay, and porosity, among other fields, and it is based on the FAO Soil Map of the World linked to a global database of over 1300 soil pedons (sample cores). The spatial resolution of the Reynolds maps is 5 minutes and there are two layers: 0-30 cm and 30-100 cm. These maps were spatially resampled to simulation resolution (1/4 or 1 degree) for GLDAS, and vertically inter/extrapolated to 0-2 cm, 2-150 cm, and 150-350 cm. These depths mainly were chosen to match the most common set of depths originally used in Mosaic. Certain model parameters are indexed based on a soil texture class and different model uses different texture class. Therefore a routine is included in LDAS to compute texture class based on fractions of sand, silt, and clay in a given grid cell. Currently, the top layer texture information is used in all soil layers. The soil color map used by CLM was interpolated from a 2 x 2.5 degree global map from the National Center for Atmospheric Research (NCAR).

In GLDAS2 products, our approach is to stay with model’s default parameter datasets as much as possible, as opposed to conforming models to use the GLDAS standard parameter datasets as done in GLDAS1. The soil texture map was used if provided by the model developer, otherwise, it was computed based on fractions of sand, silt, and clay as mentioned above. The version of Noah model in GLDAS2 uses the FAO 16-category soil texture class. The map is a hybrid of 30-second STATSGO over CONUS and 5-minute FAO elsewhere, which is available from the NCAR RAL website. The top layer map was resampled to the GLDAS 1/4 and 1 degree resolution.

GLDAS Soil Texture

GLDAS2 Noah soil texture for each 1/4 grid box. There are 16 classes.
Soil texture used in GLDAS2/Noah

GLDAS2/Noah Texture Binary Datafiles: 1/4 degree, 1 degree
Fortran code to read data: 1/4 degree, 1 degree
GrADS Control Files: 1/4 degree, 1 degree

GLDAS Soil Porosity

GLDAS soil porosity for each 1/4 grid box in the 0-2 centimeter depth range. The scale ranges from 0.35 to 0.65. The highest values of porosity are located across Canada in the boreal forests and northern Europe and Asia. The lowest values are across Australia and parts of central Asia and the middle east.
Soil Porosity used in GLDAS1/Mosaic

FAO Porosity for MOSAIC Binary Datafiles: 1/4 degree bottom, middle, top; 1degree bottom, middle, top
Fortran code to read data: 1/4 degree, 1 degree
GrADS Control Files: 1/4 degree bottom, middle, top,; 1degree bottom, middle, top

GLDAS Soil Color

GLDAS soil color (used by CLM) for each 1/4 grid box. There are eight classes.
Soil Color used in GLDAS1/CLM2

GLDAS Fraction of Silt

The fraction of silt for each 1/4 grid box in the 0-2 centimeter depth range. The scale ranges from 0.1 to 0.9. The highest fraction of silt is located across northeastern Asia with values from 0.4 to 0.8. The remainder of the world has values generally ranging from 0.2-0.4.
Fraction of Silt used in GLDAS

Fraction Silt Binary Datafiles: 1/4 degree, 1 degree
Fortran code to read data: 1/4 degree, 1 degree
GrADS Control Files: 1/4 degree, 1 degree

GLDAS Fraction of Clay

The fraction of clay for each 1/4 grid box in the 0-2 centimeter depth range. The scale ranges from 0.1 to 0.9. The majority of the world has values ranging from 0.1 to 0.4. Parts of eastern South America and Africa, central Asia, and India have higher values ranging from 0.4-0.6.
Fraction of Clay used in GLDAS

Fraction Clay Binary Datafiles: 1/4 degree, 1 degree
Fortran code to read data: 1/4 degree, 1 degree
GrADS Control Files: 1/4 degree, 1 degree

GLDAS Fraction of Sand

The fraction of sand for each 1/4 grid box in the 0-2 centimeter depth range. The scale ranges from 0.1 to 0.9. Large areas in Africa, Australia, western Asia, and northern North America have values ranging from 0.6-0.9. The majority of the world has values ranging from 0.3-0.6 while the lowest values are located in northeastern Asia with values ranging between 0.2-0.3.
Fraction of Sand used in GLDAS

Fraction Sand Binary Datafiles: 1/4 degree, 1 degree
Fortran code to read data: 1/4 degree, 1 degree
GrADS Control Files: 1/4 degree, 1 degree