つつあるChange in progress
つつある presents a change as currently unfolding toward a new state. It is formal and process-focused, and the endpoint has not yet been reached.
A process moving in a direction
The construction works best with verbs of change: something spreads, declines, recovers, develops, forms, disappears, or approaches a new state. It gives the reader a mid-process view rather than presenting the change as complete.
Typical developments
The subject can be a social trend, a technical development, or a person's gradual recovery.
Transitional process versus established result
つつある emphasizes movement toward an endpoint. The broader ている form can instead describe a result that is already established.
Looking back at an unfinished process
The final ある can be put in the past when describing a process that was underway at a past reference point. This does not itself say whether the process was eventually completed.
More examples
少子化は地方の学校運営にも影響を及ぼしつつある。
The declining birthrate is beginning to affect the operation of schools in regional areas as well.
Analyze海岸の生態系は徐々に回復しつつある。
The coastal ecosystem is gradually recovering.
Analyzeこの地域では、古い商店街の姿が失われつつある。
In this area, the traditional character of the old shopping districts is gradually disappearing.
Analyze交渉は合意に向けて進展しつつあります。
The negotiations are progressing toward an agreement.
Analyze新しい働き方が若い世代の間に定着しつつある。
New ways of working are becoming established among younger generations.
Analyze当時、地域経済は危機から立ち直りつつあった。
At the time, the regional economy was recovering from the crisis.
AnalyzeThe past form presents the recovery as underway at that past point.