6. Summary and Discussion
In this paper, CAS-LSM, which included lateral flow, water use, nitrogen
discharge and river transport, soil freeze thaw front dynamics, and
urban planning, was implemented into CAS-FGOALS-g3. When compared
against observations, the surface climate CAS-FGOALS-g3 simulations
showed reasonable distributions in the land surface variables, including
the 2-m temperature, precipitation, latent heat flux, river ocean
discharge, soil moisture, snow fraction, and surface albedo. For the
temperature, the seasonal temperature cycles at high-latitude and middle
latitude regions were closer to the observations than those in tropical
regions, while comparison of the regionally averaged seasonal cycles of
the precipitation with the observation did not show obvious trends in
terms of the latitude. For the other variables, they generally presented
an overall reasonable comparison with the observations.
Also assessed were the new capabilities of the model with the
implementation the CAS-LSM. Several of these aspects will be evaluated
in greater detail that in other papers within the special issue of the
Chinese Academy of Sciences Climate and Earth System Models (CAS-FGOALS
and CAS-ESM) and Applications special issue in the Journal of
Geophysical Research: Atmosphere and the Journal of Advances in Modeling
Earth Systems. Apparent modification of the groundwater was introduced
by including a GLF module. This allowed us to model the spatial
variability of the groundwater lateral flow, which may lead to
considerable differences in the bio-geophysical and bio-geochemical
aspects of the land surface, and thus have potential effects on climate
processes under climate warming. For anthropogenic groundwater use, over
extraction in three representative over extraction regions, northern
India, North China, and the western coast and central regions of the USA
may lead to increased evapotranspiration.
The inclusion of the FTF scheme enabled the model to simulate the
seasonal variation of the freeze and thaw process. It was seen that the
simulated FTF-derived permafrost extent was comparable to that seen in
the observations. Aside from the FTFs, incorporating schemes related to
riverine nitrogen transport and human activities into the model was
shown to be an effective way to monitor the global river water quality,
and evaluate the performance of the global land surface modeling. The
overall results of the new scheme suggested that the model was a
potentially useful tool for studying the effects of land-surface
processes on the global climate, especially those that experience human
interventions. In future work, such as the special issue just mentioned,
we will present more detailed results of our investigations of the
interactions between the land and the atmosphere at large scales.