BEIJING (AP) - Rising temperatures over the next few decades will unleash storms, floods and drought across China's Yangtze River Basin, a new report says, raising the prospect of catastrophe for a region that is home to nearly a third of the country's population.

While ecosystems along China's longest river are threatened by climate change, it's not too late to save them if proper mitigation measures are taken, said the report issued Tuesday by the environmental group WWF.

In the past two decades, temperatures in the river basin area have risen by an average of 1.8 degrees Fahrenheit (1 degree Celsius), causing a spike in flooding, heat waves and drought, said the report, the largest assessment yet on the impact of global warming on the Yangtze basin area, where some 400 million people live.

Data collected from 147 monitoring stations along the 700,000-square-mile (1.8 million-square-kilometer) area showed temperatures rose by 0.59 degrees Fahrenheit (0.33 degrees Celsius) during the 1990s. Additional findings show that between 2001 and 2005, the basin's temperature rose on average another 1.28 degrees Fahrenheit (0.71 degrees Celsius).

"Extreme climate events such as storms and drought disasters will increase as climate change continues to alter our planet," said Xu Ming, the lead researcher on the report, which included expert contributions from the China Academy of Sciences, the China Meteorological Administration and other academic institutions.

Over the next 50 years, temperatures will continue to climb by an average of 2.7 degrees Fahrenheit (1.5 degrees Celsius) to 3.6 degrees Fahrenheit (2 degrees Celsius), which will only increase the frequency of natural disasters, the report warned.

The consequences of global warming are particularly dire for a region that contributes 35 percent of the nation's total grain production and 41 percent of China's gross domestic product. The region, which cuts across the length of China, is also home to rare and endangered species such as the giant panda and the Yangtze River dolphin.

Crops such as corn, winter wheat and rice will see clear drops in production, with the rice harvest alone dipping between 9 percent and 41 percent by the end of the century, the report said. Natural habitat such as grasslands and wetlands have receded steadily in recent years, while rising sea levels triggered by global warming will make coastal cities such as Shanghai more vulnerable.

Adaptation is a must for large developing nations such as China, which is particularly vulnerable to climate change because of its population, complex climate and relatively low level of economic development, said James Leape, director general of WWF-International, formerly known as World Wildlife Fund.

"While the whole world rises to meet the challenge of climate change, we must prepare for impacts that are already inevitable," he said.

Countermeasures include strengthening existing infrastructure - such as river and dike reinforcements, transport and power supply systems, the report said. Other steps include adjusting crop systems and switching to hardier strains. Early warning systems and emergency preparedness planning were also key, it said.

Leape said the urgency of climate change requires that world leaders gathering for a U.N. summit in December reach an agreement on a global framework on reducing the greenhouse gases that have triggered global warming.

"The next 40 days are of supreme importance. It's clear we will only get an effective response to climate change if the world's heads of state come together to forge a bold global agreement," he said.

He also said that China's President Hu Jintao and President Barack Obama have an opportunity to lay the groundwork for consensus when they meet at a major summit this weekend in Singapore and next week in Beijing.