What phenomenon can high humidity lead to in urban areas?

High humidity in urban areas can contribute significantly to the urban heat island effect. This phenomenon occurs when urban regions experience higher temperatures than their rural surroundings, primarily due to human activities and alterations in land cover. High humidity can intensify the urban heat island effect by increasing the moisture content in the air, which can lead to more heat being retained.

Additionally, high humidity can also enhance the discomfort felt by residents due to the combination of high temperatures and moisture, leading to a higher energy demand for cooling and an increased likelihood of heatwaves. High levels of moisture can also exacerbate the absorption of heat by surfaces like asphalt and concrete, raising local temperatures further.

In contrast, the other options relate to different environmental factors and impacts, illustrating how specific conditions may produce varying outcomes. For instance, reduced air quality often correlates with pollution levels rather than humidity alone, while increased ice formation is a concern in colder climates rather than humid urban areas. Less vegetation growth can occur due to various urban planning choices rather than humidity levels directly influencing plant life in a general sense.