Estimations of surface temperature and subsurface heat flux following forest removal in the south-west of Western Australia

Ground surface temperature and subsurface heat flux following forest removal for agricultural development have been estimated using temperature-- depth profiles measured in the Collie River Basin, Western Australia. Temperature measurements have been done in water filled piezometer tubes to depths of 30-50 m, 19 years after forest removal and the establish- ment of annual pasture and cereal crops in areas of about 100 ha. Two parameters, change in average surface temperature and thermal diffusivity of the strata, were estimated by optimization to minimize the deviation of predicted from observed temperature-depth profiles. The increases in average annual temperatures for the ground surface 19 years after tree removal were estimated to be 3.4, 3.8 and 4.1°C in Wights, Dons and Lemon catchments with average rainfall of 1120, 800 and 820 mm yr-1, respectively. The estimated increase in ground surface temperature in a I ha area where forest was partially removed in Wights catchment was 2.2°C, and in 15 ha of agriculturally developed area cleared to parkland (trees at 20 m spacing) in Dons catchment the increase was 1.6°C. Subsurface heat fluxes between the ground surface and I m depth are predicted to become positive (upward) again 208 years after forest removal in Wights catchment and 46 years after parkland forest removal in Dons catchment.