Complex sentence: The cool climate and abundant rainfall have made Barbacena a center for flower production--the city is the biggest producer of flowers in Minas Gerais, and is nicknamed "City of Roses".
Split into simpler sentences: The cool climate and abundant rainfall have made Barbacena a center for flower production. Barbacena is the biggest producer of flowers in Minas Gerais, and the city is nicknamed "City of Roses".