Response in Diurnal Cycle of Land Surface and Air Temperature to Deforestation (Invited Presentation)

Recent studies have shown the impacts of historical land use land cover changes (namely deforestation) on hot temperature extremes; contradictory temperature responses have been found between studies using observations and climate models. However, different types of surface temperature (land surface skin temperature T_s, and near surface air temperature T_2m) are commonly used in the observation- and model-based studies respectively. This inconsistency in the use of temperature variables is not inconsequential, and the relationship between deforestation and various temperature changes can be entangled, which casts doubt on comparisons between observations and model simulations. In this study, the responses in the diurnal cycle of summertime T_s and T_2m to deforestation are investigated using the Community Earth System Model (CESM). For the daily maximum, opposite responses are found in T_s and T_2m. Due to decreased surface roughness after deforestation, the heat at the land surface cannot be efficiently dissipated into the air, leading to a warmer surface but cooler air. For the daily minimum, strong warming is found in T_2m, which exceeds daytime cooling and leads to overall warming in daily mean temperatures. By comparing a number of CMIP5 models and satellite-based estimations, we find that the models can capture the observed land surface (T_s) warming, but discrepancies exist in T_2m. Our work highlights the need to investigate the diurnal cycles of temperature responses in land cover change studies. Furthermore, consistent treatment of temperature variables should be applied in future comparisons involving observations and climate models.