The sea level around Shanghai is expected to rise by up to 16 centimeters in the next 20 years, putting the city in danger of being submerged and threatening water supplies, according to research recently completed by experts at East China Normal University, the Jiefang Daily reported Saturday.

"The rise in sea level endangers the entire city. The whole of Shanghai, including the most heavily-populated areas, could be overwhelmed by flooding," Cheng Heqin, an expert from the Institute of Estuarine and Coastal Research at the university and a member of the research team, told the Global Times.

According to the research by Cheng and her team, the sea level around Shanghai will rise by 5 to 8 millimeters per year over the next 20 years, which is above the world average.

"Shanghai is safe now only because it is protected by sea defense systems. But the average ground level is already below the average high tidal level. This means if it weren't for the flood prevention walls, the city would already be beneath water at times of peak tides," she said, adding that the city has to continuously build and upgrade flood defenses.

The rising sea level also poses a threat to the water supply for the city's more than 23 million residents, the research found.

"More than 70 percent of Shanghai's water supply comes from the Qingcaosha Reservoir. The rise in sea level will reduce the amount of time per year when we can draw fresh water from there. This will be a big problem in securing residents' daily water needs," Cheng said.

The rising sea level means that by 2030, freshwater will not be available from the Qingcaosha Reservoir for an average 2.11 days per year. For Shanghai's other two reservoirs - Chenhang and the Dongfengxisha - the average will be 0.54 and 0.15 days per year respectively, according to the research.

The research team has submitted a plan for dealing with the problem to government authorities, which includes suggestions for ensuring the maintenance of the fresh water supply.

"Since Shanghai is at the end of the Yangtze River, its supply of water is severely influenced by the water projects along the upper reaches. The national authorities should step in and ensure reasonable distribution of water resources along the river," Cheng said.

The various water projects upriver, including the Three Gorges Dam, the Gezhou Dam, and the South-to-North Water Diversion Project, contribute to the decrease of the water volume in the lower reaches, and a consequent rise in salinity, which endangers the local water reservoirs, she said.