Vatra se širi područjem.

Se is the clitic used with many Croatian verbs that are reflexive or middle-voice in meaning. Here, širiti se means to spread.

So:

• širiti = to spread something, to expand something
• širiti se = to spread, to expand, to extend on its own

In this sentence, the fire is not spreading something else; the fire itself is spreading, so Croatian uses širiti se.

Compare:

• Vatrogasci šire crijevo. = The firefighters are extending/spreading the hose.
• Vatra se širi. = The fire is spreading.

Širi is the 3rd person singular present tense form of širiti se.

It matches vatra, which is singular:

• ja se širim = I spread
• ti se širiš = you spread
• on / ona / ono se širi = he / she / it spreads

Since vatra is grammatically singular, the verb is širi.

Područjem is the instrumental singular of područje.

• nominative: područje
• instrumental: područjem

In this sentence, the instrumental is used to express movement through, across, or over an area. So područjem tells you the space through which the fire is spreading.

This is a common use of the instrumental in Croatian, especially with verbs of movement or distribution.

Both can be possible in Croatian, but they are not always used in exactly the same way.

• kroz područje = through the area
• područjem = through/across the area, throughout the area

Using the bare instrumental, as in širi se područjem, often sounds a bit more compact and natural in formal or descriptive language. It presents the area almost as the medium or space in which the spreading happens.

So Vatra se širi područjem is a normal and natural way to say that the fire is spreading through the area.

Yes, vatra is a feminine noun.

That matters for agreement in some parts of Croatian, especially adjectives and past participles. In this present-tense sentence, the verb form širi does not show gender, so you do not see a special feminine ending on the verb here.

But you can see the gender in other contexts, for example:

• velika vatra = a big fire
• Vatra se proširila. = The fire spread.
  Here proširila shows feminine singular agreement.

Croatian does not have articles like the or a/an.

So vatra can mean:

• fire
• the fire
• sometimes even a fire

The exact meaning depends on context. The same is true for područjem, which can be understood from context as the area, an area, or just area in a more general sense.

Yes. Croatian word order is more flexible than English word order, although some orders sound more natural than others depending on emphasis.

The neutral order here is:

• Vatra se širi područjem.

Other possible orders include:

• Područjem se širi vatra.
• Vatra područjem se širi. (possible, but less neutral)

Changing the order usually changes the focus or emphasis, not the basic meaning.

For example:

• Područjem se širi vatra. puts more attention on the area.

Also note that se usually stays in the second position area of the clause, because it is a clitic.

In this meaning, the important dictionary form is širiti se.

That is because se is not optional here if you mean to spread intransitively. If you just look up širiti, you may get the transitive meaning to spread something, to widen something, to extend something.

So for learners, it is best to remember this pair:

• širiti nešto = to spread/extend something
• širiti se = to spread, to expand

Yes, širiti se is imperfective. It describes an ongoing process: the fire is spreading.

A common perfective partner is proširiti se.

Compare:

• Vatra se širi područjem. = The fire is spreading through the area.
  Ongoing process.
• Vatra se proširila područjem. = The fire spread through the area / has spread through the area.
  Completed event.

This imperfective vs. perfective contrast is very important in Croatian.

A rough pronunciation is:

POD-roo-chyem

A few helpful points:

• č sounds like ch in church
• j sounds like y in yes
• je together often sounds like ye

So područjem is approximately pod-ROO-chyem, with the stress typically on the first syllable: POD-ručjem.

No, not in standard Croatian for this meaning.

Without se, širiti normally expects an object:

• Vatra širi dim. = The fire is spreading smoke.
• Vjetar širi plamen. = The wind is spreading the flame.

If you want to say that the fire itself is spreading, you need se:

• Vatra se širi.

So in your sentence, se is necessary.