2.1 CAS-LSM
Detailed descriptions of the model improvements and the performance of
CAS-LSM in the offline mode (i.e., forced with observed meteorology) was
mainly documented by Xie et al. (2018). The following series of papers
provided reference for the many schemes used here: Xie et al. 2012; Zeng
et al. 2016a, 2016b, 2018; Zou et al. 2014, 2015; Zeng et al. 2016b,
2017; Gao et al. 2016, 2019; and Liu et al. 2019. For reference, we have
included a schematic diagram that depicts the additional processes and
functionality that exists within CAS-LSM (Fig. 1). The schemes for GLF,
human water use, FTFs, anthropogenic nitrogen discharge, and urban
planning, were implemented into CLM4.5 (Oleson 2013) to produce CAS-LSM,
which now considered the abovementioned processes. CLM4.5 was developed
by the National Center for Atmospheric Research. This model included
bio-geophysical and bio-geochemical mechanisms and energy, and mass
fluxes from the land to the atmosphere, and was the land-surface
component of the Community Earth System Model 1.2.0 (Hurrell et al.
2013). The bio-geophysical processes included solar and longwave
radiation interactions with vegetation canopies and soil, momentum and
turbulent fluxes from the canopies and soil, heat transfer in soil and
snow, hydrology of canopies, soil, and snow, and stomatal physiology and
photosynthesis. The bio-geochemical processes included vegetation
photosynthesis, phenology, the carbon and nitrogen cycles,
decomposition, and wildfires (Lindsay et al. 2014). Also contained in
CLM4.5 was an interactive crop-management model, which simulated crop
growth and its effect on land processes. A sub-gridded hierarchy of land
units, soil profiles, and plant-function types was used in CLM4.5 to
describe the heterogeneity within each grid cell. Different land uses,
such as varieties of vegetation, lakes, urban areas, and glaciers, were
addressed separately even if they coexist in a given grid cell. The
CAS-LSM, building upon CLM4.5, coupled the GLF, HWR, FTFs, AHR, UWU and
DIN as optional configurations, with the target being more complete land
surface modeling.