4.2 Evapotranspiration, soil water storage, and runoff
The seasonal cycle of the regional average latent heat flux is shown in
Fig. 4. Generally, the CAS-LSM simulated values of the latent heat flux
followed the observations, except with an overall underestimation in the
nine representative regions. The general underestimation of the seasonal
cycle was apparent, except for Amazon, which generally followed that of
the observations (although with an underestimated climatology). Overall,
the peaks of the seasonal cycle were smaller in the other eight places
relative to those seen in the observations, among which India displayed
the worst result.
The differences in the mean soil water content between MAM and SON
between the model simulation and GLDAS2 (Rodell et al. 2009) are shown
in Fig. 5. While the simulations agreed well with the observations in
general (Figs. 5(a–b)), the value magnitudes of the simulations were
smaller than that of GLDAS2 in regions of the Amazon, southern and
central Africa, North America, southern and eastern Asia, and Australia.
This indicated weaker seasonal variations in the simulated soil water
content. The hydrology and snow parameterization schemes in the LSM may
be largely responsible for these biases.
River discharge to oceans in the CAS-LSM simulations was calculated via
the RTM (Branstetter and Famiglietti 1999), which transported grid-cell
runoff to oceans via pathways that approximate the paths of the real
global river network. Overall, the total simulated river discharge into
oceans was scattered around the observations (Fig. 6), with some
underestimations at some stations, especially in those that have lower
annual discharge. As the total discharge into the world’s oceans was
directly related to land precipitation minus evapotranspiration, these
underestimations may be due to precipitation bias in the model. In the
simulations, the most poorly simulated large rivers were the Congo and
Orinoco Rivers, where far too much discharge was simulated for the Congo
River (more than 100% discharge than observed) and far too little
discharge from the Orinoco River (less than 50% discharge than
observed).