Bioclimatology is defined in the preface to Advances in Bioclimatology as "the study of the relations between the physical environment and the form and function ofliving organisms". Such a definition largely confines the discipline to the proximity of the land surface, the interface between the atmospheric boundary layer, vegetation and the soil surface.. Physical climatology is concerned with the processes by which energy and mass are transferred, converted and stored in the Earth-atmosphere system (Oke 1988). The transfer of energy occurs in three modes: conduction, convection and radiation. Radiation is the transfer of energy by the rapid oscillations of electromagnetic fields. These oscillations may be considered as travelling waves, characterized by wavelength A. In environmental physics and bioclimatologywe are concerned with wavelengths in the approximate range ofO.001-100/-lm (l/-lm = 10-6 m = 1000 nm = 10 4 A).Solar radiation is the sole source of energy to living organisms, directly in the case of plants and indirectly to animals -including man. All physical and biological processes at and near the land surface are driven by energy from the sun. Shortwave radiation falls in the 0.15-3 /-lm range and longwave radiation lies in the range 3-100/-lm. Ultraviolet (UV) radiation has wavelengths between 0.001 and OA/-lm, i.e., 1-400nm. UV-C radiation (A < 280nm) never reaches the Earth's surface because of absorption by the atmosphere; the 280-320nm range is called UV-B; and UV-A comprises the 320-400nm part of the spectrum. UV-A and UV-B radiation is of major significance for human health and plays a role in biological productivity.All processes, including the biological, involve energy transformation or transfer. The energy balance describes the energy available to land-surface processes and how this energy is used. Sellers (l965) observes that "the physical state of any entity, from a small leaf to a whole continent is determined by the way it utilizes the available energy". The radiation and energy balances are