Lebanon, Jan. 11 -- Tent encampments housing thousands of Syrian refugees looked more like islands half sunk in water. Women waded knee-deep in muddy water to move around. Others pumped water out of flimsy tents that left mattresses soaked and destroyed foodstuffs and furniture.

A five-day storm that battered Lebanon with heavy rain and snow has had a devastating effect on thousands of refugees living in tents dotting eastern Lebanon's Bekaa valley, displacing many whose shelters were either flooded or destroyed by snow.

"I lost everything inside," said Umm Fawaz standing outside her tent with water up to her knees. She said she had to sleep for five nights on a chair because of the water.

The U.N. refugee agency said Thursday that 361...