TOKYO — Rising geopolitical tensions between China and the United States have begun to affect the flow of global data as new undersea cables connecting China to the rest of the world are expected to be significantly reduced.China has been hailed as a future undersea network hub that will form a vital artery for international communications, but it is expected to lay only three cables after this year, less than half of the number planned by Singapore. The lack of subsea projects is also expected to put pressure on the construction of data centers in the country.Undersea cables form the backbone of the Internet, carrying 99% of the world’s data traffic. Some 140,000 kilometers of such cables will be completed this year, three times as many as five years ago, according to US market research firm TeleGeography. The growth reflects growing demand for data traffic driven by the popularity of video streaming and cloud services.On April 10, Google announced a $1 billion project to build two undersea cables connecting Japan, Guam and Hawaii.