Heat waves in southern China

Prof. LAU Ngar-Cheung, Gabriel

The characteristics of heat waves (HWs) in southern China in 1979–2010 are studied by using both reanalysis and station datasets. Guangdong Province of China (GDPC) is taken as an example. It is found that the westward movement of the western North Pacific subtropical high (WNPSH) is the primary factor for large-scale HWs occurring in GDPC. When an HW occurs, a hot and dry atmospheric column prevails over southern China. The region is overlaid by anomalous subsidence, which leads to warming, and clear sky, which causes greater solar heating. HWs are accompanied by an anomalous high pressure center and anticyclone near the surface, with anomalous land–sea northwesterly flow, thus reducing sea–land moisture transport and drying the atmosphere over land. The evolution of the high pressure anomaly and high temperature is associated with the westward displacement of WNPSH, with a prominent positive anomaly in 500-hPa height migrating westward. All these features associated with HWs in GDPC coincide with high-temperature extremes in the whole region of southern China and parts of Indochina. Significant increases in HW frequency (+0.19 events decade⁻¹), HW days (+2.86 days decade⁻¹), the duration of the longest event (+0.38 days decade⁻¹), and the hottest temperature of the hottest event (+0.23°C decade⁻¹) are also observed. These upward trends are more prominent in the Pearl River delta (PRD) region, and urbanization contributes to nearly 50% of the increase in HW frequency in PRD. It is also noticed that HWs are commencing earlier and ending later, and urbanization may advance the timing of the onset of HW events.