China's ecology and environment have undergone historic and profound improvement over the last decade, according to a series of reports published by the Chinese Academy of Sciences on Tuesday.

The five reports feature the latest data and survey results of national freshwater resources, wetlands, mountains, water conservation in arid northwest areas, and environmental conditions in the country's three major urban clusters: Beijing-Tianjin-Hebei, the Yangtze River Delta, and Guangdong-Hong Kong-Macao Greater Bay Area.

According to the reports, China had 2,670 natural lakes over 1 square kilometer in size in 2020, totaling 80,662 sq km. The water quality of 70 percent of mid-size to large lakes has improved over the decade.

This has also led to the gradual increase of biodiversity in lake systems. In Poyang Lake, China's largest freshwater lake, the number of wintering waterfowl rose from 357,000 to 689,000, from some 50 species of birds.

Wetlands are a major ecosystem rich in biodiversity and also regulate water and filter waste from the landscape, hence their nickname of the "kidneys of the Earth".

China has one of the world's largest and most diversified wetland ecosystems, the reports said. In 2020, it had 412,000 sq km of wetlands, the most in Asia.

Chinese wetlands currently hold over 55.5 billion metric tons of fresh water, and each hectare of wetland can remove 1,000 kilograms of nitrogen and 130 kg of phosphorus on average per year.

From 2015 to 2020, the total area of wetlands underwent a net increase of 903 sq km. By the end of 2020, there were nearly 1,200 artificial wetlands, 750 more compared to a decade ago.

China's wetlands are rich in biodiversity, hosting over 1,691 species of flora and 296 wetland bird species. About 73 of these plants and 91 of the bird species are rare and protected.

"The role of wetlands in safeguarding water and ecological security is becoming more prominent. They also play an important role in addressing global climate change," the reports said.

With nearly two-thirds of its land covered by mountains and plateaus, these ecosystems play a crucial role in providing natural resources, biodiversity, and safeguarding environmental security, the reports said.

Over the past decade, natural mountain conservation areas have increased by 14.4 percent to around 1.17 million sq km.

As for water conservation in the northwest, the surface water area has increased by 161 sq km on average annually for nearly a decade. Water use in agriculture has also decreased from 95.8 percent in 2012 to 90.9 percent in 2021.

Beijing-Tianjin-Hebei, the Yangtze River Delta, and the Guangdong-Hong Kong-Macao Greater Bay Area urban clusters account for around 5 percent of China's land area, but are home to 25 percent of its population and contribute nearly 40 percent of its GDP.

"They are the core engines of economic growth, but intense levels of human activity have placed enormous stress on the ecology and environment," the reports said.

Over the last decade, environments in the three regions have steadily improved, most notably in terms of air quality.

From 2012 to 2021, the annual PM2.5 density decreased by 53.1 percent in Beijing-Tianjin-Hebei, 54.2 percent in the Yangtze River Delta, and 47.2 percent in the Guangdong-Hong Kong-Macao Greater Bay Area.