Study Shows Wildfire Smoke Can Make Clouds Drop Less Rain
2021-08-30
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1A new study suggests that smoke from wildfires can change how clouds store water and could lead to less rainfall.
2The research comes as western parts of the United States are currently experiencing drought conditions after several years of intense wildfire activity.
3A team of scientists took to the skies in western U.S. states during the summer of 2018 to study the effects of wildfire smoke on clouds.
4They flew a C-130 research airplane through clouds with instruments to measure gas and particle levels.
5In 2018, California suffered its most destructive wildfire season ever.
6Other western states, including Oregon, Colorado, and Washington, have also experienced intense wildfire activity in recent years.
7Cynthia Twohy is an atmospheric scientist at NorthWest Research Associates and Scripps Institution of Oceanography in San Diego.
8She led the new study, which recently appeared in Geophysical Research Letters.
9Twohy said in a statement she decided to center on cloud research because she wondered if there was a link between the increase in wildfires and a lack of rain.
10"I started thinking, 'What are the long-term effects of this? We have drought, and we have a lot of wildfires, and they're increasing over time. How do clouds play into this picture?'" she said.
11Clouds contain a collection of water droplets that form from vapor in the atmosphere.
12When these droplets condense onto each other within a cloud, they become heavier and eventually fall as rain.
13But the water condensation process requires a solid substance for the vapor to attach to.
14Different kinds of particles rising up from the Earth's surface can reach clouds and enable this process.
15The new study found that smoke from wildfires contains small particles that affect the way droplets form in clouds.
16The main effect was the amount of water droplets formed.
17The team reported the smoky clouds contained about five times the number of droplets as non-smoky clouds.
18But data also showed that the droplets in smoky clouds were much smaller, about half the size, as those in the clouds without wildfire smoke.
19It is that size difference, the researchers say, that could reduce the amount of rainfall.
20This is because small droplets are less likely to grow and eventually fall to the ground as rain.
21"Because of their small droplet sizes, these smoky clouds are expected to reflect more light and produce less rain than clouds in clean air," the study states.
22The finding could mean that active wildfire seasons in the western U.S. may in fact lead to less rain and more drought, the researchers said.
23"We were surprised at how effective these primarily organic particles were at forming cloud droplets and what large impacts they had on the microphysics of the clouds," Twohy said.
24The researchers noted that past studies had also found similar changes in cloud droplets related to wildfire smoke in the Amazon.
25However, the new study points out that, in addition to the cloud droplet changes, "a number of complex and competing" elements might also be affecting climate in the U.S. West.
26Twohy also noted that different kinds of clouds behave differently.
27The current study examined changes in small, cumulus clouds.
28Other kinds that sit much higher in the atmosphere can cause heavy storms, she said.
29Twohy added: "I'm hoping these results will spur detailed regional modeling studies that will help us understand the net impact of smoke on clouds and climate."
30I'm Bryan Lynn.
1A new study suggests that smoke from wildfires can change how clouds store water and could lead to less rainfall. 2The research comes as western parts of the United States are currently experiencing drought conditions after several years of intense wildfire activity. 3A team of scientists took to the skies in western U.S. states during the summer of 2018 to study the effects of wildfire smoke on clouds. They flew a C-130 research airplane through clouds with instruments to measure gas and particle levels. 4In 2018, California suffered its most destructive wildfire season ever. Other western states, including Oregon, Colorado, and Washington, have also experienced intense wildfire activity in recent years. 5Cynthia Twohy is an atmospheric scientist at NorthWest Research Associates and Scripps Institution of Oceanography in San Diego. She led the new study, which recently appeared in Geophysical Research Letters. 6Twohy said in a statement she decided to center on cloud research because she wondered if there was a link between the increase in wildfires and a lack of rain. 7"I started thinking, 'What are the long-term effects of this? We have drought, and we have a lot of wildfires, and they're increasing over time. How do clouds play into this picture?'" she said. 8Clouds contain a collection of water droplets that form from vapor in the atmosphere. When these droplets condense onto each other within a cloud, they become heavier and eventually fall as rain. 9But the water condensation process requires a solid substance for the vapor to attach to. Different kinds of particles rising up from the Earth's surface can reach clouds and enable this process. 10The new study found that smoke from wildfires contains small particles that affect the way droplets form in clouds. 11The main effect was the amount of water droplets formed. The team reported the smoky clouds contained about five times the number of droplets as non-smoky clouds. But data also showed that the droplets in smoky clouds were much smaller, about half the size, as those in the clouds without wildfire smoke. 12It is that size difference, the researchers say, that could reduce the amount of rainfall. This is because small droplets are less likely to grow and eventually fall to the ground as rain. 13"Because of their small droplet sizes, these smoky clouds are expected to reflect more light and produce less rain than clouds in clean air," the study states. 14The finding could mean that active wildfire seasons in the western U.S. may in fact lead to less rain and more drought, the researchers said. 15"We were surprised at how effective these primarily organic particles were at forming cloud droplets and what large impacts they had on the microphysics of the clouds," Twohy said. 16The researchers noted that past studies had also found similar changes in cloud droplets related to wildfire smoke in the Amazon. However, the new study points out that, in addition to the cloud droplet changes, "a number of complex and competing" elements might also be affecting climate in the U.S. West. 17Twohy also noted that different kinds of clouds behave differently. The current study examined changes in small, cumulus clouds. Other kinds that sit much higher in the atmosphere can cause heavy storms, she said. 18Twohy added: "I'm hoping these results will spur detailed regional modeling studies that will help us understand the net impact of smoke on clouds and climate." 19I'm Bryan Lynn. 20Bryan Lynn wrote this report for VOA Learning English, based on reports from the American Geophysical Union and Geophysical Research Letters. Susan Shand was the editor. 21We want to hear from you. Write to us in the Comments section, and visit our Facebook page. 22___________________________________________________ 23Words in This Story 24drought - n. a long period of time during which there is very little or no rain 25vapor - n. a substance in a gaseous state as opposed to a liquid or solid 26condense - v. to change from a gas to a liquid 27reflect - v. to send back or bounce off 28organic - adj. used in chemistry to describe chemicals that contain carbon 29impact - n. the effect a person, event or situation has on someone or something else 30cumulus (cloud) - n. a type of thick cloud that is rounded on top and has a flat base 31spur - v. to urge someone to do something or something to happen 32net - adj. complete or total