Comparison of diurnal variations of pre-summer extreme hourly rainfall between inland and coastal regions over the Greater Bay Area

This research explores interdecadal variations in the diurnal cycle of rainfall (DCR) over both inland and coastal areas of the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) in pre-summer during 1979–2020. Analysis reveals that, over the past 42 years, trends in extreme rainfall during both day and night in GBA have escalated, driven by increased frequency and intensity. Inland rainfall shows a more pronounced trend during the daytime than nighttime; conversely, coastal rainfall exhibits a more significant increasing trend at night than during the day. Metropolitan influences have intensified these diurnal variations, with notably steeper increases in daytime rainfall observed in Guangzhou and its surroundings and in nocturnal rainfall along the eastern coastal regions of the Pearl River Estuary. Daytime inland rainfall is primarily influenced by temperature, humidity, and the direction of the southwesterly monsoon. These meteorological effects are significantly amplified in urban areas such as Guangzhou, as well as in northern Foshan and western Huizhou. Nocturnal coastal rainfall is mainly affected by sea-land differences; the western shores experience significant impacts from thermal contrasts, whereas wind speed in the monsoon flow contrasts notably influences the eastern shores.