Kad pada kiša, oko štale uvijek ima više blata nego na stazi.

Kad means when here.

Yes, you can also say kada. The two are very close in meaning, but kad is usually a bit more common in everyday speech, while kada can sound slightly more formal or careful.

So both of these work:

• Kad pada kiša...
• Kada pada kiša...

Yes, literally it is rain falls.

Croatian normally expresses it is raining with the verb padati or kišiti in some contexts, but pada kiša is a very standard, natural way to say it.

So:

• pada kiša = it is raining
• literally: rain is falling

English uses a dummy subject it, but Croatian does not need that here.

Both are possible.

• Kad pada kiša... sounds very natural and neutral.
• Kad kiša pada... is also correct, but it can sound slightly more literary, rhythm-based, or more focused on kiša.

Croatian word order is more flexible than English word order. In this sentence, pada kiša is just the most natural everyday phrasing.

Kiša is in the nominative singular because it is the subject of pada.

Basic form:

• kiša = rain

Here:

• kiša pada = the rain falls / it is raining

After the preposition oko in this meaning, Croatian uses the genitive.

So:

• štala = barn, stable
• oko štale = around the barn

That is why štala changes to štale.

This is a very useful pattern to remember:

• oko kuće = around the house
• oko sela = around the village
• oko štale = around the barn

It most directly means around the barn.

In context, it often implies the general area surrounding the barn, which in natural English may sometimes feel like near the barn. But grammatically, oko is specifically around.

So the image is: in the area surrounding the barn, there is more mud.

Here ima means there is / there are in an existential sense.

So:

• ima blata = there is mud
• ima više blata = there is more mud

Croatian often uses ima where English uses there is / there are.

Notice that ima stays singular here because it is part of this existential structure, not a normal counted subject-verb pattern.

Because više meaning more is a quantity word, and after it Croatian normally uses the genitive.

So:

• blato = mud
• više blata = more mud

This is very common with quantity expressions:

• puno vode = a lot of water
• malo vremena = a little time
• više blata = more mud

Since blato is an uncountable noun here, the genitive singular blata is used.

Blato is the dictionary form, the nominative singular.

Blata here is the genitive singular form.

So:

• blato = mud
• više blata = more mud
• bez blata = without mud

The ending changes because Croatian marks grammatical function with case endings.

Nego is commonly used after comparatives, especially when comparing one thing directly with another.

Here:

• više blata nego na stazi = more mud than on the path

This is the standard way to make this kind of comparison.

A useful pattern:

• više... nego... = more... than...
• manje... nego... = less... than...

Stazi is the locative singular of staza.

The preposition na can take different cases depending on meaning:

• na stazu = onto the path, movement toward it
• na stazi = on the path, location

In this sentence, the meaning is location, not movement, so Croatian uses the locative:

• na stazi = on the path

Because Kad pada kiša is a subordinate time clause: When it rains.

In Croatian, when this kind of dependent clause comes first, it is normally separated with a comma from the main clause:

• Kad pada kiša, oko štale...

This works very much like English:

• When it rains, ...

Yes, but the meaning changes slightly.

• uvijek = always

With uvijek, the sentence says this is a regular or consistent fact:

• Kad pada kiša, oko štale uvijek ima više blata nego na stazi.
• When it rains, there is always more mud around the barn than on the path.

Without uvijek, it simply states the comparison in that situation, but less strongly as a habitual truth.

Because Croatian does not need those dummy subjects the way English does.

English says:

• it rains
• there is more mud

But Croatian can simply say:

• pada kiša
• ima više blata

This is a very common difference between English and Croatian. English often needs a grammatical subject even when it does not refer to anything specific; Croatian often does not.

Yes, it is natural.

A native speaker could also rephrase it in other ways, for example by changing word order, but the original sentence sounds normal and idiomatic.

Possible natural variants include:

• Kad pada kiša, uvijek ima više blata oko štale nego na stazi.
• Kada pada kiša, oko štale uvijek ima više blata nego na stazi.

The original version is already perfectly good Croatian.