Learn Arabic (Modern Standard): عندما يزدهر قطاع السياحة، تزيد الرحلات. - When the tourism sector flourishes, trips increase.

The root of يزدهر is ز-ه-ر (related to flowers or shining). In Form VIII verbs, the characteristic letter added after the first root letter is usually a ت. However, when the root starts with ز, the ت assimilates and changes into a د to make pronunciation smoother.

Why does the second clause use the feminine singular verb تزيد for the plural subject الرحلات?

In Arabic, non-human plurals like الرحلات (trips) are grammatically treated as feminine singular. Because of this core rule, the verb must be conjugated in the feminine singular form, which is تزيد (literally: she increases).

Why doesn't the word قطاع have the definite article ال even though the translation says 'the tourism sector'?

The phrase قطاع السياحة is an Idafa (genitive construction) meaning 'the sector of tourism'. In an Idafa, the first word never takes the definite article ال, but it automatically becomes definite because the second word, السياحة, is definite.

Why are the verbs يزدهر and تزيد in the regular present tense instead of the jussive or past tense often used in conditions?

Unlike formal conditional particles such as إن (if) or إذا, which usually force verbs into the jussive mood or past tense, the word عندما (when) functions as an adverb of time. It allows verbs to remain in the regular present indicative tense to state a general, ongoing fact.