Η κατανάλωση είναι μεγάλη.

Η is the definite article meaning the.

In Η κατανάλωση είναι μεγάλη, it is:

• feminine
• singular
• nominative

It matches κατανάλωση, which is a feminine singular noun.

In Greek, every noun has a grammatical gender: masculine, feminine, or neuter.
Κατανάλωση happens to be feminine.

That is why it goes with:

• the feminine article η
• the feminine adjective μεγάλη

This is grammatical gender, so it does not mean consumption is “female.” It is just part of how the noun behaves in Greek.

Here, κατανάλωση is in the nominative singular.

It is the subject of the sentence:

• Η κατανάλωση = the consumption / consumption
• είναι μεγάλη = is great / is high / is large

So the sentence structure is basically:

subject + verb + adjective

Είναι means is here.

It is the 3rd person singular present form of είμαι (to be).

So:

• είμαι = I am
• είσαι = you are
• είναι = he/she/it is

In this sentence, it links the subject η κατανάλωση with the description μεγάλη.

Because adjectives in Greek must agree with the noun they describe in:

• gender
• number
• often case

Since κατανάλωση is feminine singular, the adjective must also be feminine singular:

• μεγάλος = masculine
• μεγάλη = feminine
• μεγάλο = neuter

So:

• η κατανάλωση → μεγάλη

Even though μεγάλη comes after είναι, it still agrees with κατανάλωση.

Yes, μεγάλη literally means big/large/great, but in Greek it is very natural in sentences like this to express the idea of high.

So Η κατανάλωση είναι μεγάλη can mean:

• Consumption is high
• The consumption is high
• Consumption is large

English often prefers high with things like consumption, demand, spending, and levels. Greek often uses μεγάλος / μεγάλη / μεγάλο in similar contexts.

You may also hear more formal alternatives in some contexts, such as υψηλή (high), but μεγάλη is perfectly normal.

Greek uses the definite article much more often than English.

So Η κατανάλωση can sometimes correspond to:

• the consumption
• or simply consumption

depending on context.

With abstract or general nouns, Greek often sounds more natural with the article than English does. So even if the English translation drops the, the Greek article may still be there.

Normally, no. In standard Modern Greek, you usually keep the verb είναι in a sentence like this.

So the normal sentence is:

Η κατανάλωση είναι μεγάλη.

Omitting είναι would sound incomplete in ordinary speech.
You might see omission only in special styles such as:

• headlines
• notes
• very compressed language

But for normal learning and normal conversation, use είναι.

A simple pronunciation guide is:

i katanálosi íne megáli

Approximate pronunciation:

• Η = ee
• κατανάλωση = ka-ta-NA-lo-see
• είναι = EE-ne
• μεγάλη = me-GHA-lee

A few helpful notes:

• Greek stress matters.
• The accent mark shows which syllable is stressed.
• κατανάλωση is stressed on νά
• είναι is stressed on εί
• μεγάλη is stressed on γά

The sentence as given has a very neutral word order:

Η κατανάλωση είναι μεγάλη.

Greek word order is more flexible than English, so you could rearrange it for emphasis, for example:

Μεγάλη είναι η κατανάλωση.

That might emphasize μεγάλη more strongly, something like:

• It is high, the consumption
• The consumption is indeed high

But for a basic, neutral statement, the original order is the most straightforward one.

Because μεγάλη is being used as a predicate adjective after είναι.

Compare:

• η μεγάλη κατανάλωση = the big/high consumption
  (adjective directly modifying the noun)
• η κατανάλωση είναι μεγάλη = the consumption is big/high
  (adjective after is)

In the second type, Greek normally does not use an article before the adjective.