Radiation balance of natural and agricultural vegetation

Abstract The three constants of a radiation‐balance equation ‐ albedo, heating coefficient and long‐wave radiation balance at zero insolation ‐ have been derived from linear regression equations relating measurements of incident and reflected short‐wave radiation to measurements of radiation balance (all wave‐lengths) made over nine different associations of natural vegetation and two agricultural surfaces. Albedo was found to be the most important discriminant in the relationship, varying from 0.12 for a pine forest to 0.37 for vegetation in a desert wadi. The diurnal and seasonal variations were small and of limited significance. The heating coefficient varied considerably, both with date of measurement and with vegetation, but no consistent differences could be seen. The values found were very low, even negative on a number of occasions. These were associated with a mid‐day decrease in the long‐wave balance attributed to a marked increase in the long‐wave flux from the sky. The long‐wave balance at zero insolation also varied considerably with date of measurement and type of surface but showed only small differences in long‐term mean values. Daily totals of net radiation balance expressed as percentages of total incoming short‐wave radiation varied from a maximum of 58 per cent for the open water surface of a fish pond to a minimum of 25 per cent for a desert association. The ratio for most vegetation was close to 50 per cent.