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.