Different roles of dynamic and thermodynamic effects in enhanced semi‐arid warming

ABSTRACT Enhanced warming in semi‐arid regions has received much attention since it was first proposed, but the primary driver of this phenomenon remains unknown. This study applied dynamical adjustment to surface air temperature and partitioned the warming into two separate components: a thermodynamically forced component and a dynamically induced component. The results show that the mean amount of thermodynamic warming in the Northern Hemisphere in the study period 1902–2011 was 1.36 °C/109 years and that the amount of dynamic warming was 0.14 °C/109 years. In the mid‐latitude zones of Asia, Europe, and North America, the thermodynamic warming was 1.60, 1.19, and 1.32 °C/109 years, respectively, and the corresponding dynamic warming was 0.26, 0.14, and 0.09 °C/109 years. Obviously, higher thermodynamic temperature warming was observed in semi‐arid regions, suggesting that the enhanced semi‐arid warming (ESAW) is the result of local thermodynamic effects. Thus, different local thermodynamic effects are responsible for the warming discrepancies in the semi‐arid regions of Asia, Europe, and North America. Moreover, the considerable bias of Coupled Model Intercomparison Project Phase 5 (CMIP5) ensemble mean temperature trend appeared in semi‐arid regions rather than other regions indicate that the simulation of semi‐arid regions is particularly complex and difficult. (a) The surface air temperature trend during the cold season in 1902–2011 as a function of the climatological annual precipitation for the thermodynamic (red dots) and dynamic (blue dots) temperatures over the mid‐latitudes of the NH (20°–60°N). (b) The regionally averaged temperature trend in (a). Surface air temperature change in Northern Hemisphere (NH) in 1902–2011 is characterized by enhanced warming in semi‐arid regions. By applying the dynamical adjustment to temperature, this study separated the raw temperature into thermodynamic and dynamic components. It is found that the thermodynamic temperature exhibited uneven warming in the different climate regions, with particularly enhanced warming in semi‐arid regions; whereas, the dynamic temperature exhibited a nearly consistent trend over all climate regions. This enhanced semi‐arid warming is dominated by thermodynamic temperature change.