الأثر على المدينة واضح.

Because this is a nominal sentence in Arabic. In the present tense, Arabic normally does not use a separate word for is/are.

So:

• الأثر على المدينة واضح literally follows the pattern The effect on the city clear
• In natural English, we say The effect on the city is clear

If you wanted the past tense, Arabic would usually use a verb, for example كان.

The sentence has two main parts:

• الأثر على المدينة = the subject/topic
• واضح = the predicate/comment

More specifically:

• الأثر = the main noun
• على المدينة = a prepositional phrase modifying الأثر
• واضح = tells you something about that whole noun phrase

So the structure is:

• [the effect on the city] [is clear]

الـ is the Arabic definite article, meaning the.

So:

• أثر = an effect / a trace
• الأثر = the effect / the trace

In this sentence, the noun is definite, which usually means the speaker is referring to a specific, identifiable effect already understood from context.

Because المدينة means the city, not just a city.

So:

• مدينة = a city
• المدينة = the city

This usually suggests a particular city is already known from context.

Because Arabic commonly uses على with أثر when talking about an effect on something.

So:

• الأثر على المدينة = the effect on the city

This is a normal Arabic pattern. English speakers may want to translate prepositions word-for-word, but it is better to learn them as part of common expressions:

• أثر على = effect on

Because واضح is describing الأثر, not المدينة.

And أثر is:

• singular
• masculine

So the predicate appears as:

• واضح = clear/apparent (masculine singular)

If the sentence were about the city being clear, then the form would be different. But here the thing that is clear is the effect, not the city.

In this kind of sentence, the predicate is often indefinite, even when the subject is definite.

So:

• الأثر = definite subject
• واضح = indefinite predicate

This is very normal in Arabic nominal sentences.

Compare the idea:

• الرجل طويل = the man is tall
• البيت كبير = the house is big

The adjective-like predicate often appears without الـ.

In fully vocalized Classical or formal MSA, it would be:

الأثرُ على المدينةِ واضحٌ

Here is why:

• الأثرُ: nominative, because it is the subject/topic of the nominal sentence
• المدينةِ: genitive, because it comes after the preposition على
• واضحٌ: nominative, because it is the predicate of the nominal sentence

In normal everyday writing, these short vowel endings are usually omitted.

A simple pronunciation guide is:

al-atharu ʿalā al-madīnati wāḍiḥun with full case endings

Or in normal pause pronunciation:

al-athar ʿalā al-madīna wāḍiḥ

A few sound notes:

• ث in الأثر sounds roughly like th in think
• ع in على is a deep throat sound with no exact English equivalent
• ض in واضح is an emphatic consonant
• ح in واضح is a strong breathy h from the throat

No. أثر can have several related meanings depending on context, such as:

• effect
• impact
• trace
• mark
• impression

In this sentence, the context makes effect/impact the natural meaning. But it is useful to know that the word has a wider range than just one English translation.

Yes, but the current order is the most straightforward and neutral.

Normal order:

• الأثر على المدينة واضح

A more marked or literary order could put the predicate first:

• واضحٌ الأثرُ على المدينةِ

That can sound more emphatic or stylistically elevated. For most learners, the original version is the best one to use first.

Most naturally, it goes with الأثر:

• الأثر على المدينة = the effect on the city

Then واضح comments on that whole phrase:

• The effect on the city is clear

So syntactically, it is best understood as part of the noun phrase headed by الأثر.

If you wanted to say the effects on the city are clear, you would make both the noun and the predicate plural:

• الآثار على المدينة واضحة

Changes:

• الأثر → الآثار = the effects
• واضح → واضحة here, because آثار is a non-human plural, and non-human plurals usually take feminine singular agreement in Arabic

That last point is very important in Arabic grammar.