Coupling of the CAS-LSM Land-Surface Model With the CAS-FGOALS-g3 Climate System Model

The land-surface model of the Chinese Academy of Sciences (CAS-LSM), which includes lateral flow, water use, nitrogen discharge and river transport, soil freeze-thaw front dynamics, and urban planning, was implemented in the Flexible Global Ocean-Atmosphere-Land System model, grid-point version 3 (CAS-FGOALS-g3) to investigate the climatic effects of eco-hydrological processes and human activities. Simulations were conducted using the land-atmospheric component setup of CAS-FGOALS-g3 with given sea-surface temperatures and sea-ice distributions to assess its new capabilities. It was shown that anthropogenic groundwater use led to increased latent heat flux of about 20 W∙m⁻² in three groundwater overexploitation areas: North India, northern China, and central United States. The groundwater lateral flow accompanied by this exploitation has led to deepening water table depth in these regions. The derived permafrost extent from the soil freeze-thaw front (FTF) was comparable to observations, and the inclusion of FTF dynamics enabled simulations of seasonal variations in freeze-thaw processes and related eco-hydrological effects. Inclusion of riverine nitrogen transport and its joint implementation with the human activity scheme showed large dissolved inorganic nitrogen concentrations in major rivers around the globe, including western Europe, eastern China, and the U.S. Midwest, which were affected by nitrogen retention and surface water use during transport. The results suggest that the model is a useful tool for studying the effects of land-surface processes on global climate, especially those influenced by human interventions.