ame ga yandara, kouen de sanposimasu.

やんだら comes from the verb やむ, which means to stop in the sense of rain, snow, wind, noise, pain, and so on coming to an end.

The form is built like this:

• やむ → dictionary form
• やんだ → plain past form
• やんだら → if/when it stops

So 雨がやんだら means if/when the rain stops.

This is a very common point of confusion.

In Japanese, the conditional 〜たら is made from the past plain form + ら, but that does not mean the whole sentence is talking about the past.

So:

• やんだ by itself = stopped
• やんだら = if/when it stops / after it stops

With 〜たら, the past form is just part of the grammar pattern.

It can feel like all three, depending on context.

In this sentence, 雨がやんだら、公園で散歩します most naturally suggests:

• when the rain stops
• after the rain stops
• sometimes if the rain stops

The nuance is that the second action happens once the first condition is met. In everyday context, this often sounds closer to when/after than a purely hypothetical if.

が marks 雨 as the subject of やむ.

So 雨がやんだら means when the rain stops.

Using が here is very natural because it simply identifies what is stopping.

If you used 雨は, it would sound more like you are setting up rain as a topic or contrast, such as:

• As for the rain, when it stops...
• If the rain stops, but maybe something else is different...

In this sentence, が is the straightforward choice.

Because で marks the place where an action happens.

Here, 散歩します is the action, and it happens in the park, so:

• 公園で散歩します = take a walk in the park

By contrast, に usually marks:

• destination
• point in time
• existence target

So 公園に would sound more like to the park, not in the park doing the walking.

Both can relate to walking, but the nuance is a little different.

• 散歩します = take a walk / go for a walk
• 歩きます = walk

散歩します emphasizes walking as a leisurely activity.
歩きます is more general and can just mean the physical act of walking.

So this sentence sounds natural if the idea is a pleasant walk in the park, not just moving on foot.

Yes. Japanese often leaves out the subject when it is understood from context.

So 公園で散歩します could mean:

• I will take a walk in the park
• we will take a walk in the park
• sometimes even someone will take a walk in the park

In many real conversations, the listener already knows who is being talked about, so Japanese does not need to say it explicitly.

Japanese non-past covers both:

• present
• future

So 散歩します can mean:

• I take walks
• I will take a walk

In this sentence, because it follows the condition 雨がやんだら, it is naturally understood as future:

• When the rain stops, I’ll take a walk in the park

Yes. The form itself can allow more than one interpretation.

Depending on context, it could mean:

• a plan: I’m going to take a walk in the park once the rain stops
• an intention: I’ll take a walk in the park if the rain stops
• a repeated habit: When it stops raining, I take a walk in the park

Without extra context, many listeners will understand it as a simple future plan or intention.

No, it is not strictly necessary, but it is very common and helpful.

The comma shows a pause between:

• the condition: 雨がやんだら
• the main action: 公園で散歩します

So it makes the sentence easier to read, especially in writing.

Yes, that is also possible, but the nuance is a little different.

• 公園で散歩します focuses on the park as the place where the activity happens
• 公園を散歩します can sound more like walking through or around the park

In many situations, 公園で散歩します is the more basic and expected way to say take a walk in the park.

やむ is an intransitive verb. That means the thing stopping is the subject itself.

Examples:

• 雨がやむ = the rain stops
• 雪がやむ = the snow stops

You do not usually use it to mean someone stops the rain. It describes the event coming to an end on its own.