Urban areas rainier from heat and smog

A new study has found that many cities around the world receive more rain than their surrounding areas. This phenomenon, known as the urban rainfall effect, is similar to the urban heat island effect.

Researchers, led by Dev Niyogi from the University of Texas at Austin, analyzed satellite data on rainfall in 1056 cities and nearby rural areas between 2001 and 2020. They discovered that over 60% of cities were “wet islands,” experiencing more rainfall than their surroundings. Some cities, like Ho Chi Minh City and Sydney, had more than 100 millimeters of additional rainfall per year compared to their surroundings.

The study also revealed that factors such as heat absorption by buildings, urban roughness, air pollution, and lack of vegetation influence how cities affect rainfall. Larger cities with higher populations were more likely to be wet islands, and cities in temperate, tropical, and coastal regions showed the largest rainfall anomalies.

Interestingly, the difference in rainfall between wet islands and their surroundings has nearly doubled over the study period, attributed to urbanization and climate change. While current weather models do not account for the impact of cities on rainfall, future city planning may consider this information to manage flooding and drought risks effectively.

Understanding the urban rainfall effect can help cities make informed decisions to mitigate extreme weather conditions.