Research Background
The Pearl River Delta (PRD), the core of the GBA, is one of the world’s fastest-urbanizing regions, with a population exceeding 60 million. Over the past two decades, large areas of cropland and natural vegetation have been converted into impervious urban surfaces. Between 2001 and 2019, cropland, water bodies, barren land, and forest/grassland decreased by 44.03%, 8.05%, 50.22%, and 0.43%, respectively, while construction land increased by 20.05%. These dramatic land-use changes have fundamentally altered the regional energy and water balance, and intensified the urban heat island (UHI) effect and reshaped the local precipitation patterns.
Key findings
“Urbanization and anthropogenic heat are amplifying regional climate effects,” said Prof. Gan. “These local factors not only increase temperatures but also alter atmospheric circulation, leading to more frequent and intense rainfall events.”
Fig. 1. Summer mean surface albedo in (a) the CROP and (b) the URB experiments. The 2-meter summer mean air temperature (unit: °C) difference is shown in (c) between the URB and CROP experiments, and (d) between the URB-AH and URB experiments. The summer mean precipitation rate (unit: mm h-1) difference is shown in (e) between the URB and CROP experiments, and (f) between the URB-AH and URB experiments.
Research highlights
The study highlights the important role of the GBA’s coastal setting in amplifying impacts of human activity and climate change. Interactions between land, ocean, and atmosphere create a feedback loop: urban surfaces store heat, rising warm air draws in moisture from the South China Sea, and the enhanced convection leads to heavier rainfall.
“Urban expansion strengthens vertical motion and transports moisture to higher levels of the atmosphere,” added Dr. Lai. “This enhances rainfall, even as surface evaporation is reduced by impervious urban land.”
The findings suggest that continued urbanization will further intensify heatwaves and increase flood risks during the summer monsoon season. By isolating the effects of land-use change and anthropogenic heat, the study provides new insights into how megacities can influence regional climate systems.
The authors emphasize the need to better represent urban processes in climate models for improving weather prediction and supporting climate-resilient urban planning. The results are particularly relevant for the GBA, where high population density, complex terrain, and coastal exposure jointly create significant climate challenges.
The study, titled “Warming and wetting induced by urbanization and anthropogenic heat over a fast-developing large river delta,” has been published in the Journal of Applied Meteorology and Climatology (JAMC) and was featured in the American Meteorological Society (AMS) Science Headlines in March 2026.
Fig. 2. Sumer mean area-averaged vertical integrated moisture flux convergence terms (moisture advection term and wind convergence term, unit: mm hh−1) over urban areas within the PRD in CROP, URB, URB-AH experiments.
Scientific significance
Led by Prof. Gan Jianping, Chair Professor and Head of the Department of Ocean Science at HKUST and Director of the Centre for Ocean Research in Hong Kong and Macau, the research demonstrates how urbanization is transforming regional weather systems. Their findings show that urbanization has significantly increased both temperature and rainfall. Air temperatures in urban areas increased by more than 1°C compared to surrounding rural regions, while anthropogenic heat further elevated surface temperatures by up to 0.5°C. At the same time, rainfall intensifies over urban centers and downwind areas, driven by enhanced moisture convergence and strengthened land–sea circulation.
For more detailed spatiotemporal feature analysis, please refer to: Lai, W., & Gan, J. (2026). Warming and wetting induced by urbanization and anthropogenic heat over a fast-developing large river delta. Journal of Applied Meteorology and Climatology, 65(4), 537-550. https://doi.org/10.1175/JAMC-D-25-0138.1.