Sanaa's Old City, inhabited without interruption for more than 2,500 years is literally melting.
The deluge risks finishing off the destruction of its distinctive buildings with their ochre brick facades and white latticework windows, experts say. The foundations were already weakened by bombings in Yemen's long war.
The city has since 2014 endured a conflict that pits government forces against Houthi rebels who hold much of the country's north.
Flooding is common in Yemen at this time of year, blighting the poorest country on the Arabian peninsula. At least 172 people have been killed across Yemen since mid-July, according to official sources and local authorities.
The war has claimed tens of thousands of lives, and displaced some three million people. About 24 million Yemenis are dependent on some form of humanitarian aid.
UNESCO said it "profoundly regrets the loss of life and property in a number of historic centres in Yemen, including in the World Heritage sites".
