RESEARCH ARTICLE
10.1002/2015MS000526
A gridded global data set of soil, intact regolith, and
sedimentary deposit thicknesses for regional and global
land surface modeling
Jon D. Pelletier
1
, Patrick D. Broxton
2
, Pieter Hazenberg
2
, Xubin Zeng
2
, Peter A. Troch
3
, Guo-Yue Niu
3
,
Zachary Williams
1
, Michael A. Brunke
2
, and David Gochis
4
1
Department of Geosciences, University of Arizona, Tucson, Arizona, USA,
2
Department of Atmospheric Sciences,
University of Arizona, Tucson, Arizona, USA,
3
Department of Hydrology and Water Resources, University of Arizona,
Tucson, Arizona, USA,
4
National Center for Atmospheric Research, Boulder, Colorado, USA
Abstract Earth’s terrestrial near-subsurface environment can be divided into relatively porous layers of
soil, intact regolith, and sedimentary deposits above unweathered bedrock. Variations in the thicknesses of
these layers control the hydrologic and biogeochemical responses of landscapes. Currently, Earth System
Models approximate the thickness of these relatively permeable layers above bedrock as uniform globally,
despite the fact that their thicknesses vary systematically with topography, climate, and geology. To meet
the need for more realistic input data for models, we developed a high-resolution gridded global data set
of the average thicknesses of soil, intact regolith, and sedimentary deposits within each 30 arcsec (1 km)
pixel using the best available data for topography, climate, and geology as input. Our data set partitions the
global land surface into upland hillslope, upland valley bottom, and lowland landscape components and
uses models optimized for each landform type to estimate the thicknesses of each subsurface layer. On hill-
slopes, the data set is calibrated and validated using independent data sets of measured soil thicknesses
from the U.S. and Europe and on lowlands using depth to bedrock observations from groundwater wells in
the U.S. We anticipate that the data set will prove useful as an input to regional and global hydrological and
ecosystems models.
1. Introduction
1.1. Problem Statement
Moisture within the relatively porous weathered material between Earth’s surface and unweathered bed-
rock plays a central role in the land-atmosphere exchange of energy, water, and carbon fluxes as well as
dynamic vegetation [e.g., Zeng et al., 2008]. In particular, moisture availability in the shallow subsurface can
provide a critical constraint on the short-term and long-term memory of previous climatic forcing [e.g.,
Koster et al., 2004]. The depth of the rooting zone also has a significant impact on the time scale of moisture
variability [Wang et al., 2006]. Over the tropical forest, the availability of moisture from the deep vadose
zone helps to maintain evapotranspiration and vegetation greenness over the dry season [e.g., Zeng et al.,
1998; Saleska et al., 2007; Sakaguchi et al., 2011].
Inclusion of data on the thicknesses of the relatively porous subsurface layers above bedrock is essential for
accurate land surface modeling of the energy, water, carbon cycle, and dynamic vegetation. In general, a
lower boundary condition is needed to solve the governing equation for vadose zone moisture, but no con-
ditions are satisfactory without a depth to bedrock (DTB) estimate [e.g., Zeng and Decker, 2009]. Since con-
straints on permeable layer thickness are not available at present, land models (for hydrometeorology,
climate, and carbon-cycle studies) often assume a globally uniform value. Even the use of an unconfined
aquifer in land models implicitly assumes a globally constant bedrock depth [e.g., Lawrence et al., 2011]. In
the North American Monsoon region, Gochis et al. [2010] found that assuming a uniform soil or permeable
layer thickness can limit land surface model performance at the sites studied; the main impact of account-
ing for thinner soils is to increase the dynamic range of sensible and latent heat fluxes when compared with
simulations using a fixed soil thickness of 2 m. At high latitudes, Lawrence et al. [2008] demonstrated the
importance of deep soil layers on the simulation of permafrost.
Key Points:
We have quantified the thicknesses
of permeable layers above bedrock
for Earth System Models
We distinguish among uplands and
lowlands, using optimal models for
each to predict depth to bedrock
The data set honors the geologic,
topographic, and climatic controls on
permeable layer thicknesses
Supporting Information:
Supporting Information S1
Correspondence to:
J. D. Pelletier,
jdpellet@email.arizona.edu
Citation:
Pelletier, J. D., P. D. Broxton,
P. Hazenberg, X. Zeng, P. A. Troch,
G.-Y. Niu, Z. Williams, M. A. Brunke, and
D. Gochis (2016), A gridded global data
set of soil, immobile regolith, and
sedimentary deposit thicknesses for
regional and global land surface
modeling, J. Adv. Model. Earth Syst., 8,
41–65, doi:10.1002/2015MS000526.
Received 31 JUL 2015
Accepted 8 DEC 2015
Accepted article online 13 DEC 2015
Published online 22 JAN 2016
Corrected 2 FEB 2016
This article was correc ted on 2 FEB
2016. See the end of the full text for
details.
V
C
2015. The Authors.
This is an open access article under the
terms of the Creative Commons
Attribution-NonCommercial-NoDerivs
License, which permits use and
distribution in any medium, provided
the original work is properly cited, the
use is non-commercial and no
modifications or adaptations are
made.
PELLETIER ET AL. GRIDDED GLOBAL DATA SET OF SOIL THICKNESS 41
Journal of Advances in Modeling Earth Systems
PUBLICATIONS
