U.S. Geological
Survey
Open-File Report 00-335
Online version 1.0
Web only
By Konstantine P. Georgakakos1,2 and Diane E. Smith1
ABSTRACT
A monthly snow-pack and soil- moisture accounting model is formulated for application
to each of the climate divisions of the conterminous United States for use in climate impacts-assessment
studies. Statistical downscaling and bias-adjustment components complement the
model for the assimilation of large-scale global climate model data. Simulations of the
formulated model driven by precipitation and temperature for the period 1931-1998 produce
streamflows that are broadly consistent with observed data from several drainage basins in the
US. Simulated historical soil moisture fields reproduce several features of the available observed
soil moisture in the Midwest. The simulations produce large-scale coherent seasonal patterns of
soil moisture field- moments over the conterminous US, with high soil moisture means over
divisions in the Ohio Valley, the northeastern US and the Pacific Northwest, and with
pronounced low means in most of the western US climate divisions. Characteristically low field-standard-
deviations are produced for the Ohio Valley and northeastern US, and the Pacific
Northwest in winter, and the southwestern US in summer. Differences in extreme standardized
anomalies of soil moisture over the historical record range possess high values (2.5 - 3) in the
central US where the available water capacity of the soils is high.
An application of the model to exemplify the methodology for determining projected US
monthly soil moisture fields under control and greenhouse gas forcing is also documented.
Climate simulations of the coupled global climate model from the Canadian Centre for Climate
Modeling and Analysis were used for these sensitivity examples. The climatology of the
control-run soil moisture fields reproduces several characteristic features of the historical soil
moisture climatology. Simulations with forcing by a 1% greenhouse-gas- increase scenario show
that for at least the first few decades of the 21 st Century somewhat drier-than-present soil
conditions are projected, with highest drying trends found in the southeastern US. The soil
moisture deficits in most areas are of the same order of magnitude as the soil moisture field-standard-
deviations aris ing from historical natural variability. In a companion paper (Brumbelow
and A. Georgakakos, 2000), the monthly soil moisture fields for the historical, control and
greenhouse-gas-increase runs are used to initialize a site-specific daily crop yield model at the
start of the growing season. Assessments of potential impacts of climate variability and trends
on irrigation requirements and crop yield across the conterminous US are made. |
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Last modified: 11.22.00