Recommendations for future research
For detailed surveys of the availability of relevant data sets and
requirements for future observational, theoretical, and modelling work,
reference should be made to the appropriate sections of Eagleson (1981) and
ICSU/WMO (1983, sect. 5 and annexes). Space precludes more than a brief
statement of the more important needs. In the following, these needs are
classified into three types: (a) observational studies; (b) improvements in GCM
parametrizations; and (c) GCM experiments.
- Data sets on actual surface albedo are
needed both for GCM experiments and to provide a basis for future assessments of
- The dependence of vegetation albedo on moistness of
foliage and of soil should be studied to allow specification of these
dependences in GCMs (a).
- The dependence of albedos on soil moisture as
well as on vegetation should be included in GCMs on the basis of the above
studies and used in vegetation change experiments (b, c).
- Research is needed to
overcome the fundamental parametrization problems of transfer of theory and
models based on microscale observations to the GCM grid scale, allowing for
inhomogeneities of soils, slopes, vegetation, precipitation, etc. (a,b).
- Particular efforts are needed on the parametrization of runoff, which is
generally very crudely represented in GCMs (b).
- The evaporation of
intercepted rainfall and the effects of root depth variations need to be
included in GCMs to allow proper assessments of the sensitivities to vegetation
- GCM experiments are needed to assess the sensitivities to
variations in runoff and root depths associated with vegetation changes
- Assessments of GCM
formulations in relation to the surface stress are desirable in view of the
large sensitivity to its formulation found in the GISS model by Hansen et al.
- Sensitivity experiments are needed to estimate the GCM
response to perturbations of surface roughness (z0) (c).
actual variations of z0 are poorly known. Observational studies of
the relation of z0 to vegetation are required if GCMs are found to be
sensitive to it (a).
The simulation of cloudiness in GCMs is generally poor. Special attention
should continue to be given to this aspect of GCMs to represent realistically
the feedbacks between clouds and surface parameters