Some cities receive more rain than their surroundings
Paul Brown / Alamy
Urban environments have a significant impact on weather patterns, causing numerous cities worldwide to experience a higher level of precipitation compared to their neighboring regions. This revelation could potentially reshape urban development strategies in the future.
According to Dev Niyogi from the University of Texas at Austin, “Just as urban areas exhibit an urban heat island effect, they also demonstrate an urban rainfall effect.”
Niyogi and his team analyzed satellite data on rainfall from 2001 to 2020 in 1056 cities and their proximate rural areas across various climatic zones. Their research unveiled that more than 60% of these cities were termed “wet islands,” receiving more rainfall than their surroundings, while some cities displayed the opposite phenomenon as “dry islands.” For instance, cities like Ho Chi Minh City and Sydney were identified as the wettest anomalies, receiving over 100 millimeters more rainfall annually than their surroundings, whereas Seattle and Rio de Janeiro featured among the ten driest cities.
While previous studies have recognized the impact of individual cities on rainfall patterns, Niyogi asserts that this study is the first to present a global pattern of such influence. He emphasizes the necessity of viewing rainfall and urban areas as interconnected entities.
Cities can augment or diminish precipitation through various mechanisms. Factors such as heat absorption by urban infrastructure, building height, air pollution, and surface coverage all play a role in altering weather dynamics over urban regions. The study indicated that larger and more densely populated cities were more likely to exhibit wet island characteristics, with cities in temperate, tropical, and coastal zones exhibiting the most significant anomalies.
The investigation also noted a consistent increase in the average difference in rainfall between wet islands and surrounding areas over the studied period. This escalation, from an average of 37 to 62 millimeters more rainfall per year, can be attributed to rapid urbanization and escalating temperatures due to climate change, which elevate atmospheric water vapor levels.
Although current weather and climate models do not explicitly incorporate the influence of cities on rainfall, Niyogi anticipates the potential integration of such data into urban planning strategies in the future. This could involve tailored approaches for managing floods in wet cities and enhancing precipitation in drier urban areas.
Vocabulary List:
- Precipitation /prɪˌsɪpɪˈteɪʃən/ (noun): Any form of water liquid or solid that falls from the atmosphere and reaches the ground.
- Augment /ɔːɡˈmɛnt/ (verb): To make something greater by adding to it; increase.
- Urbanization /ˌɜːrbənəˈzeɪʃən/ (noun): The process of making an area more urban or city-like.
- Anomalies /əˈnɒməliːz/ (noun): Deviations from the common rule; irregularities or exceptions.
- Interconnected /ˌɪntərˈkɒnɛktɪd/ (adjective): Mutually joined or related; connected with one another.
- Mechanisms /ˈmɛkəˌnɪzəmz/ (noun): Structures or processes that underlie an operation or concept.
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