Irannejad, P., Y. Shao and A. Henderson-Sellers, 1995:
Surface soil moisture in AMIP/PILPS land-surface schemes (Diagnostic Subproject
12). Abstracts of the First International AMIP Scientific Conference, Monterey,
California, 39.
Soil moisture is a key component in landsurface parameterization schemes
as it is closely related to evaporation and plays an important role in
the hydrological cycle and in soil-vegetation biochemistry and determines
the partition of precipitation into runoff and evaporation and the net
available energy into latent and sensible heat fluxes. One of the major
research activities in the PILPS/AMIP subproject (No. 12) is to understand
current landsurface parameterizations used in climate models and to assess
their performances. As part of this evaluation 14 landsuface schemes conducted
15 numerical experiments using the atmospheric forcing and surface parameters
derived from HAPEX-MOBILHY and the performance of the schemes were evaluated
against these observational data. The intercomparison of the simulations
revealed a large difference of about 200 mm in total soil moisture content
for a 1.6 m soil layer. After careful adjustment of the parameters characterizing
the soil hydraulic properties and those of surface properties, the disagreement
between the models decreased to 70 mm for the bare soil period and about
100 mm in the growing season, which is still quite large. All models could
correctly describe the annual trend of soil moisture in a qualitative way,
but compared to observation most schemes underpredicted the total soil
water content, especially during the growing season. In contrast to the
total soil layer, models generally overestimated the soil water content
in the root zone. Most schemes conserve water well, but the soil moisture
budget is achieved in very different ways in different models. The ranges
of annual evaporation as well as runoff-drainage are as large as 250 mm.
The partitioning of surface energy into latent and sensible fluxes is closely
related to the partitioning of precipitation into evaporation and runoff-drainage.
Current evaluations of soil moisture are unreliable even with carefully
specified landsurface parameters and accurate atmospheric forcing. The
prediction of soil moisture in global models seems to be extremely uncertain
at present.