Temperature change and urbanisation in a multi-nucleated megacity: China's Pearl River Delta

This paper investigates urbanisation and temperature indices, over four decades in a multi-nucleated megacity, China's Pearl River Delta (PRD). Daily mean minimum, maximum and mean temperatures (T_min, T_max and T_mean) have increased considerably above background warming rates. However, only weak to moderate relationships are observed between trends in local urban surface area surrounding climatic stations, and T_min used as a proxy for UHI development. While 5 out of 21 stations with high increase in both T_min and degree of urbanisation, showed moderate relationship (R = 0.51), another 8 stations with low urbanisation showed significant increase in T_min. This suggests warming from factors other than local urban development on T_min. Since PRD contains eight cities over 4 million population, and a semi-continuous urbanised area due to merging of urban centres, a regional heat island circulation, or heat dome model is invoked. The observed increase in T_max above background warming rates for 14 stations, is more difficult to explain as T_max is not generally affected by urbanisation. This is attributed to high surface energy flux in the afternoon, and anthropogenic energy use in dense urban districts. The regional heat dome circulation over PRD suggests local temperatures will increase further, even without further local developments.