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.

Albedo

1. Data sets on actual surface albedo are needed both for GCM experiments and to provide a basis for future assessments of changes (a).
2. The dependence of vegetation albedo on moistness of foliage and of soil should be studied to allow specification of these dependences in GCMs (a).
3. 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).

Hydrology

1. 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).
2. Particular efforts are needed on the parametrization of runoff, which is generally very crudely represented in GCMs (b).
3. 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 changes (b).
4. GCM experiments are needed to assess the sensitivities to variations in runoff and root depths associated with vegetation changes (c).

Roughness

1. 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. (1983) (b).
2. Sensitivity experiments are needed to estimate the GCM response to perturbations of surface roughness (z₀) (c).
3. the 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).

General

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 (b).