yaei ha abunai.

It is read:

やえい は あぶない

• 野営 = やえい
• は = written ha but pronounced wa here because it is the topic particle
• 危ない = あぶない

So the whole sentence sounds like:

Yaei wa abunai.

野営 is a noun meaning camping, encampment, or camping out in the open.

It is a bit more formal or literary than the everyday loanword キャンプ.

It can also behave like a verbal noun, so you may sometimes see:

• 野営する = to camp out / to bivouac

In this sentence, though, 野営 is simply the topic noun.

は marks the topic of the sentence.

So 野営は危ない means something like:

• As for camping out, it is dangerous
• Camping out is dangerous

The particle は does not directly mean is. It shows what the sentence is talking about.

Structure:

• 野営 = topic
• は = topic marker
• 危ない = dangerous

Japanese does not need a separate word like English is in sentences with i-adjectives.

危ない is an i-adjective, and i-adjectives can act as the predicate by themselves.

So:

• 野営は危ない。 = Camping is dangerous.

There is no missing verb here. The sentence is already complete.

危ない is an i-adjective.

That matters because i-adjectives change form directly:

• 危ない = dangerous
• 危なくない = not dangerous
• 危なかった = was dangerous
• 危なくなかった = was not dangerous

In this sentence, 危ない is in its plain present form.

Because this is the plain style.

• 野営は危ない。 = plain / casual
• 野営は危ないです。 = polite

Both are grammatical.

A learner should know, though, that 危ないです is common in modern Japanese conversation, even though the older textbook-style explanation can make it seem unusual. It is perfectly normal polite speech.

Not especially in casual conversation.

A native speaker is more likely to say:

• キャンプは危ない。 = Camping is dangerous.

野営 sounds more like:

• formal
• written
• military
• survival/outdoors
• literary

So the sentence is correct, but the word choice is a bit more specialized than everyday speech.

By itself, it sounds most naturally like a general statement about camping out.

Because は marks a topic, the feeling is:

• As for camping out, it’s dangerous
• Camping out is dangerous

Context could make it refer to a specific situation, but without context, it sounds general.

Normally, standard Japanese is written without spaces:

野営は危ない。

Spaces are often added only in learning materials to make the structure easier to see.

So the spaced version is helpful for study, but the normal written form has no spaces.

Yes, but it changes the nuance.

• 野営は危ない。 = As for camping out, it is dangerous / a general statement
• 野営が危ない。 = Camping out is the dangerous thing / puts more focus on 野営

Using が can sound more contrastive or more like identifying what is dangerous.

For a simple general statement, は is very natural.

Yes.

• 野営は危ない。
• 野営は危険だ。

Both mean that camping out is dangerous, but the nuance is a little different:

• 危ない is more everyday and direct
• 危険だ sounds slightly more formal or objective

So:

• 危ない = feels conversational
• 危険だ = feels more formal, technical, or official

Yes.

Because 野営 can function like a verbal noun, you can say:

• 野営する = to camp out
• 野営した = camped out
• 野営は危ない = Camping out is dangerous

So the noun form and the verbal form are both possible, depending on the sentence structure.