Climate change and extreme weather events pose a grave challenge to the China's food supply, agricultural researchers have warned.

Gu Lianhong, a senior researcher with Oak Ridge National Laboratory in the US, said the lab's research had shown climate change will cause China's per capita grain output will dramatically drop after 2020, even taking technological progress into consideration.

The study suggests the projected geographical pattern of earth's surface temperature will dramatically increase in the late 21st century (2090-2099). This will cause more extreme weather and climate events to impact such industries as agriculture, Gu said.

He stressed that increasing droughts and heavy precipitation, more intense tropical cyclones and warmer days will very likely happen globally.

"These are all closely related with grain output," Gu said.

The researcher made the remarks on the sidelines of the International Forum on the Mitigation of Desertification, Land Degradation and Drought (DLDD) in World Dryland, which ended over the weekend.

By the 2050s, freshwater availability in Central, South, East and Southeast Asia is projected to decrease, particularly in large river basins, Gu said. The regions' coastal areas, especially heavily populated mega deltas, will be at great risk due to increased flooding from the sea or rivers.

Because China is the world's most water-deficient country, climate change will definitely harm its agricultural production, Gu said.

The researcher's warning came as China is faced with a challenging grain situation this summer because of strong rainfalls in the south during the summer harvest season. Other problems include droughts in northern grain production areas and lingering low temperatures in the south.

In the past few years, the country has experienced more frequent extreme weather events against the backdrop of global climate change. These include severe droughts, ice storms, sandstorms and floods that harm the economy and security.

The severe drought in Southwest China, which has lasted since late 2009 and is one of the worst in decades, has affected about 8.3 million hectares of arable land. It also left at least 17.9 million people and 12.4 million heads of livestock facing water shortages as of this May, the Office of State Flood Control and Drought Relief Headquarters said in a statement.

A report by McKinsey & Co released last year said extreme drought caused by a "high climate change scenario" could more than triple crop losses in Northeast China. They could reach 13.8 million metric tons, or 12 percent of the total, by 2030.

The average annual temperature in China has increased by 0.5 C to 0.8 C, a little higher than the global average, over the past 100 years and especially in the past five decades. But the country's precipitation volume did not change much during the period, China's National Climate Change Program said in June 2007.

The average temperature in China will possibly rise 1.3 C to 2.1 C from 2000 to 2020, increasing the risks of extreme weather and climate events in the country, the plan said.

China must maintain an annual grain output of 500 million tons to feed the nation's 1.3 billion people, the Ministry of Agriculture said.

The country's summer grain output rose six years in a row to exceed 123.35 million tons in 2009, 2.6 million tons more than the previous year.