With the climate set to get warmer from greenhouse gases, Chinese scientists predicted yesterday that fresh water for agriculture will diminish in China, reducing crop yields in the years ahead.

In a paper published in Nature, they said the temperature in China had risen by 1.2 degrees Celsius since 1960 and will increase by another 1 to 5 degrees Celsius by 2100.

"Such a pronounced summer warming would inevitably enhance evapo-transpiration, increasing the risk of water shortage for agriculture," wrote the researchers, led by Piao Shilong of the Center of Climate Research at Beijing University.

"Climate change may induce a net yield reduction of 13 percent by 2050."

Transpiration is similar to evaporation and refers to the loss of water vapor from plants.

They forecast that rice yields would decrease by 4 to 14 percent, wheat by 2 to 20 percent and maize by zero to 23 percent by the middle of the 21st century.

China only has 7 percent of the world's arable land, but needs to feed 22 percent of the world's population. Although its total water resource is huge in absolute terms, it is only 25 percent of the per capita world average.

Its climate has also become drier in the north, which holds 18 percent of the total water resource and 65 percent of total arable land, they added.

Heavy rainfall and flooding, meanwhile, have occurred in the southern parts of the country.

Higher temperatures have also led to the spread of pests, they said.

"Countrywide, a 4.5 percent reduction in wheat yields is attributed to rising temperatures over the period 1979-2000," they wrote.