Source of China's three main rivers, Yangtze, Yellow and Lancang rivers, last year recorded the largest volume of water outflow from the Qinghai-Tibet Plateau in three decades, according to local hydrological authorities.

According to the provincial hydrological bureau of the northwestern Qinghai, the outflow of three rivers' headwaters, called Sanjiangyuan in Chinese, amounted to 77.63 billion cubic meters last year, a record high over the past 30 years or 26.6 percent more than the average level.

The total included 29.74 billion cubic meters through the Yangtze River, 16.62 billion cubic meters through Lancang River, and 31.27 billion cubic meters through the Yellow River, said Li Qijiang, deputy director of the bureau.

Gao Gui'en, an engineering official with the provincial Sanjiangyuan administration office, attributed the significant increase of water outflow to more rainfalls and ecological conservation efforts, including returning grazing land to grassland and artificial rainfall.

Sanjiangyuan, known as the "water tower of China" with an altitude of 4,000 meters, is an important ecological conservation area in China, influencing a large territory of the country.