A Review of the Thermodynamic Characteristics, Formation Mechanisms, and Changing Trends of Extreme Heat Events in Northwest China under Global Climate Change

Abstract

Against the backdrop of global warming and strong regional land-atmosphere coupling, extreme heat events in Northwest China are exhibiting a significant increasing trend of being "more frequent, more persistent, and more intense." Based on a composite diagnosis of 63 summer extreme heat events in Northwest China from 1958 to 2022, and integrating international and domestic research progress, this paper systematically reviews the spatiotemporal changes, thermodynamic structure and energy budget, formation and maintenance mechanisms of extreme heat in this region, as well as its coupling relationships with global warming, large-scale circulation, and underlying surface changes. The results indicate that diabatic heating in the boundary layer (approx. 800 hPa) often acts as a trigger, which is subsequently sustained by the synergistic effects of subsidence-induced adiabatic warming and strong zonal warm advection, with meridional advection playing a significant modulating role. The mid-troposphere (approx. 650 hPa) is co-controlled by zonal advection, vertical adiabatic heating, and diabatic heating. The upper troposphere (approx. 350 hPa) is dominated by subsidence-induced adiabatic warming and zonal warm advection, where diabatic heating often acts as a suppression term. This is fundamentally different from the typical "WPSH + warm-moist airflow" type heatwaves in eastern China. Upper-level anticyclones, blocking heights, and "heat dome" structures facilitate the accumulation of heat within the boundary layer through stable stratification and weak ventilation. Global warming elevates the meaning of the temperature distribution and amplifies the probability of tail events, while sensible-heat amplification and near-surface and boundary-layer heat accumulation under dry-soil conditions further enhance the intensity and persistence of extremes. CMIP family models consistently project a significant increase in the number of heatwave days, duration, and cumulative intensity in Northwest China under 1.5–3°C warming scenarios. This paper identifies key shortcomings such as sparse observations, inadequate parameterization of the boundary layer and dust-radiation-cloud interactions, and weaknesses in event attribution and Subseasonal-to-Seasonal (S2S) probabilistic forecasting. It proposes research pathways oriented towards multi-source data fusion, convection-permitting scale modeling, three-component attribution, and inter-departmental risk governance.