BANGKOK — In southern China, the worst drought in at least 50 years has dried up farmers’ fields and left tens of millions of people short of water.

But the drought has also created a major public relations problem for the Chinese government in neighboring countries, where in recent years China has tried to project an image of benevolence and brotherhood.

Farmers and fishermen in countries that share the Mekong River with China, especially Thailand, have lashed out at China over four dams that span the Chinese portion of the 3,000-mile river, despite what appears to be firm scientific evidence that low rainfall is responsible for the plunging levels of the river, not China’s hydroelectric power stations.

This weekend, a group of affected countries — Myanmar, Laos, Cambodia and Vietnam — are meeting in Thailand to discuss the drought, among other issues.