THE ROLE OF SURFACE ALBEDO IN THE SOLAR RADIATION ENVIRONMENT: THE IMPACT OF LAND-COVER CHANGE IN THE CENTRAL NORTH ISLAND, NEW ZEALAND

Radiative forcing due to land-cover change is likely to be among the strongest climate forcing mechanisms on local and regional scales. Hence, understanding the solar radiation environment and the way it has changed, and may change in the future, due to natural process and anthropogenic activity is of importance for both prediction and management. Yet, albedo measurements are still often not well characterised within climate models and ground-truthing seldom takes place.

To investigate the relative effect of these changes and to characterise albedo, a novel field campaign was undertaken in Pureora, Central North Island, New Zealand. Between November 2003 and 2004, measurements of incoming (direct and diffuse) and outgoing solar radiation, temperature, wind speed and direction, and rainfall were recorded at four sites. The sites represent the four key past, present and expected future land-cover types: Native old-growth forest; native wetland; production pasture; and production forest (pinus radiata). The sites are located in adjacent watersheds to control for latitude, elevation, aspect and slope, and are large enough (edge greater than 5km from measurement site) to be truly representative of each type; hence differences in outgoing radiation and temperature can be attributed to land-cover type and the difference in albedo.

Results are discussed in terms of their impact on landscape productivity on local and regional scales, and their contribution to climate change on local, regional and potentially global scales. Preliminary findings suggest relatively low albedos for the production sites; indicating that these land-uses create a warming effect when compared to the native sites. This may be enhanced by the ecological productivity of the native environments, as much of the radiation that is not reflected is used for ecological processes; in production environments this is not the case as diversity is negligible and ecological function is comparatively low. Further, fertilisation (and other enhancement) of production environments adds more energy to the system, thereby acting creating another positive feedback.