Learn Spanish (Latin America): Cuando el crecimiento es rápido, la ciudad cambia. - When the growth is fast, the city changes.

You would change the verb cambia to solía cambiar. To make the first half of the sentence match this past context, you would also change es to the imperfect form era, resulting in: Cuando el crecimiento era rápido, la ciudad solía cambiar (When the growth was fast, the city used to change).

Why does this sentence use the present indicative es after cuando instead of the subjunctive?

We use the indicative (normal) present tense after cuando when stating a general fact or something that happens habitually, as is the case in this sentence. You only use the subjunctive after cuando when referring to an event that hasn't happened yet, such as a specific future action.

The word crecimiento looks related to the verb crecer (to grow). Is -miento a common noun ending?

Exactly! The suffix -miento is frequently added to verbs to turn them into nouns, similar to "-ment" or "-th" in English. So crecer (to grow) becomes crecimiento (growth). Another common example is sentir (to feel) becoming sentimiento (feeling).

I often see rápido used to mean "quickly". Is it acting as an adjective or an adverb here?