The evaluation of urbanisation on climate change in the Pearl River Delta

Abstract

The Pearl River Delta region has been one of the regions in the world experiencing the most rapid growth since 1980s. By replacing natural surface with buildings, roads and other impervious surfaces, high solar radiation absorption and thermal capacity are resulted. It has become increasingly evident that rapidly developments would influence the climate within the immediate region. This project aims to examine the impact of the urban development to the thermal environment in the PRD, by estimating the long-time series changes of impervious surface area (ISA) and air temperatures from meteorological stations and Landsat images. From the meteorological station data, significant warming rates were found for all stations in average, minimum and maximum air temperatures over the past four decades. The warming rate of average, minimum and maximum air temperature was 0.28°C, 0.31°C and 0.30°C per decade. Among them, minimum temperatures can best measure the Urban Heat Island (UHI) intensity. The minimum temperatures are temperatures at midnight with no incoming solar radiation. The building artificial materials retain heat absorbed during daytime in urbanized area and release at night. It is found that the highest increase of minimum temperature is in Shenzhen (0.6°C/decade). There are 15 out of the 21 stations having a warming rate of minimum temperatures higher than the global rising trend. The south-western part of the PRD had experienced a higher increase of minimum temperatures compared to other parts in the same region. The daytime warming trend, represented by increasing average and maximum temperatures, may be attributed to high surface energy flux in the afternoon, and anthropogenic energy use in dense urban districts. The results of ISA in the 1km, 3km and 5km buffers created surrounding the stations were regressed against the warming rate, the ISA increase in all buffers is positively correlated to the warming rate, but only weak to moderate relationships are observed in general. A stronger relationship is demonstrated with both high increase and ISA growth. This suggests warming can be attributed to factors other than local urban development on minimum temperatures. Considering the structure of the PRD being a multi-nucleated megacity with huge population, a regional heat island circulation or heat dome model is formed due to merging of urban extents The presence of a regional heat dome circulation over the PRD implies that local temperatures should increase further, even without significant local developments. The uniqueness of this research is to consider the UHI effect in a regional scale and it is especially meaningful to urban planners to address and devise mitigating measures in regional perspectives, such as the design of green belts or green cover in urban areas, and utilization of other non-concreting building materials.