This is the 960th most frequent Japanese word.
出現
Appearance; emergence.
In this context, 出現 is used to describe the surfacing or becoming apparent of a significant issue over time.
大都市における交通渋滞の問題が近年さらに深刻に出現している。
The problem of traffic congestion in major cities has emerged more severely in recent years.
The word 出現 is used here to mean 'to appear or emerge', emphasizing the introduction of a new item or concept into the market.
市場に新しいスタイルのスマートフォンが出現した。
A new style of smartphone emerged on the market.
Here, 出現 signifies the sudden manifestation of something unusual or unexpected.