While the light rains have diminished, pollution has increased dramatically in China in the last half of the 20th century. For example, while China's population rose two and a half times in size, the emissions of sulfur from fossil fuel burning outpaced that considerably -- rising nine times.
Air pollution contains tiny, unseen particles of gas, water and bits of matter called aerosols. Aerosols -- both natural and human-caused-- do contribute to rainfall patterns, but the researchers needed to determine if pollution was to blame for China's loss of rain and how.
To find out, the team charted trends in rainfall from 1956 to 2005 in eastern China, which has 162 weather stations with complete data collected over the entire 50 years.
From this data, the team determined that both the north and south regions of eastern China had fewer days of light rain -- those getting 10 millimeters per day or less -- at the end of the 50 year timespan. The south lost more days -- 8.1 days per decade -- than the north did, at 6.9 days per decade. However, the drought-rattled north lost a greater percentage of its rainy days, about 25 percent compared to the south's 21 percent.
"No matter how we define light rain, we can see a very significant decrease of light rain over almost every station," said Qian.
Up Up & In the Way
To probe what caused the loss of rainfall, the team looked at how much water the atmosphere contained and where the water vapor traveled. Most parts of eastern China saw no significant change in the amount of water held by the atmosphere, even though light rains decreased. In addition, where the atmosphere transported water vapor didn't coincide with light rain frequency.
These results suggested that changes in
|Contact: Mary Beckman|
DOE/Pacific Northwest National Laboratory