Summer is still a few months away, but the streets of Croatia's old town of Dubrovnik are already teeming with tourists from all over the world. It's usually a sign of a strong season ahead, but this year uncertainty hangs in the air.

Global instability triggered by the Iran war and surging fuel prices have brought unpredictability to the tourism industry, including in Dubrovnik, Croatia's top Adriatic Sea destination that draws millions of visitors annually.

The stakes for Croatia’s economy are high: The tourism sector is one of the country’s key sources of income and is largely dependent on international travelers.

Though tourist numbers have been up in Dubrovnik, officials are warning nothing is guaranteed.…