Learn Turkish: Küresel iklim değiştiğinden beri selin etkisi daha kötüymüş. - Since the global climate changed, the flood's impact is apparently worse.

It uses the pattern you are currently learning for "since doing something". We start with the verb stem değiş- (to change). We add the participle suffix -dik (which becomes -tiğ due to consonant mutation and vowel harmony). Then we add the 3rd person possessive -i, a buffer -n-, and the ablative suffix -den (from). Finally, we add the word beri (since).

Why does değiştiğinden need a possessive suffix?

In Turkish, these temporal clauses act like noun phrases. The possessive suffix shows who or what is doing the action. Here, the 3rd person singular -i refers to küresel iklim (the global climate). You are essentially saying "from the global climate's changing."

What makes selin etkisi mean "the flood's impact"?

This is a specific noun compound using the genitive and possessive suffixes. Sel (flood) takes the genitive suffix -in to mean "the flood's", and etki (impact) takes the 3rd person possessive suffix -si to mean "its impact". Together, they link the two words strictly to each other to show possession or belonging.

What does the -müş suffix add to kötü (bad) at the end of the sentence?