QINGDAO -- Water levels on north China's Bohai and Huanghai seas have risen to a high not seen since 1980, oceanic authorities in East China's Shandong province announced Monday.

The North China Sea Branch of the State Oceanic Administration issued its 2012 North China Oeanic Disaster Bulletin on Monday. The bulletin said water levels on both seas have risen by more than 100 mm in comparison to last year.

Average sea water temperatures in the seas have dropped by 0.06 degrees Celsius in comparison to last year and erosion has expanded in coastline areas, the bulletin said.

Researchers have been studying the effect of sea level increases on economic development and the environment, including increases in natural disasters, coastline erosion and soil salination.

The bulletin said ocean-related natural disasters resulted in economic losses totalling 5.98 billion yuan ($949 million) last year, up 4.3 billion yuan from 2011.