Changes in Surface and Subsurface Temperatures after Clearing Forest in Western Australia

Abstract

Changes of ground surface temperature following clearing forest for agricultural development have been estimated using temperature-depth profiles measured in the Collie River Basin, Western Australia. Temperatures were measured in bore holes to depths of 30 to 50 meters 19 years after clearing and the establishment of annual pasture and cereal crops in areas of about 100ha. Three parameters, change in average surface temperature, change in amplitude of the surface temperature and thermal diffusivity of the strata were estimated by optimization to minimize the deviation of predicted from the observed temperature-depth profiles. The increase in ground surface temperature were estimated to be 3.4 and 3.8 °C in Wights and Dons catchments with average rainfall 1200 and 750 mm/year respectively. The estimated increase in ground surface temperature in a partially cleared area of Wights catchment was 2.2 °C, and in a 15 ha area cleared to parkland (trees at 20 in spacing) in Dons catchment the increase was 1.6 °C. The annual amplitude of monthly average surface temperature increased from 1.5 to 7.4 °C after clearing in Wight catchment. The thermal diffusivity estimated from the optimizing method decreases slightly with increasing depth of the potentiometric surface, because of the lower water content of soils in the recharge area.