Weather modification: cloud seeding used to create rain


Clouds gather in the sky over the southern San Joaquin Valley near Taft during a storm.

The Chinese government recently announced a vast expansion of its weather modification program, covering more than half of its country by 2025 to control the amount of precipitation (rain, hail and snow) that reaches the ground.

The announcement raised concerns among China’s neighbors across Asia who depend on the rains for much of their water needs. This could lead to claims of “rain theft,” and here’s why.

The concept of cloud seeding was discovered by Vincent Schaefer in 1946.

At the time, he was working at the General Electric laboratory creating artificial clouds in a large cold chamber kept below zero. He thought it was too hot and placed dry ice inside to further cool the compartment.

Suddenly, a cloud formed around the dry ice. It turns out that the microscopic ice crystals in the dry ice had provided an almost perfect seed on which water vapor could condense.

Working with Schaefer, physicist Bernard Vonnegut discovered that silver iodide was more effective at cloud nucleation than dry ice. Over the decades, no other molecule has been found that rivals it in creating rain.

Clouds form from the condensation of invisible water vapor on extremely small nuclei from dust, volcanoes, pollen, forest fires, pollution from cars and factories, salt from sea ​​spray or sulfite particles from phytoplankton in the oceans.

Cloud seeding increases the number of these available cores. In fact, raindrops or ice crystals might never form without them under certain atmospheric conditions.

After these discoveries, Project Cirrus, a combined effort involving government and private industry, was organized in 1947 to explore the possibilities and limits of cloud seeding.

About 20 years later, cloud seeding would be used in the Vietnam War. The US Department of Defense sowed clouds to extend the monsoon season along the Ho Chi Minh Trail during Operation Popeye from 1967 to 1972).

The objective of the program was to prevent the use of this major supply route by flooding it. Continued rains slowed truck traffic and were considered a success.

The US Air Force’s 54th Weather Reconnaissance Squadron performed most of the cloud seeding operation to “make mud, not war”.

Cloud-related activity was rumored to have contributed to heavy rains over the Woodstock festival in upstate New York. More than half a million spectators joined in the chants of “No More Rain!” during Neil Young’s performance.

After the war, the Convention on the Prohibition of Military or Other Hostile Use of Environmental Modification Techniques treaty was adopted by the United Nations General Assembly in 1976. This treaty aimed to ensure that weather modification is only used for peaceful purposes.

Unfortunately, especially during droughts, you simply cannot go out and sow clear skies; you need to have the right weather conditions with lots of clouds near or already rushing in.

Most cloud seeding operations inject silver iodide into the clouds from aircraft or from ground stations on mountain tops where updrafts carry the silver iodide into the clouds. passing clouds.

Cloud seeding helps precipitate more water from the atmosphere, like squeezing a damp sponge over the desired watershed. Yet it leaves behind a drier air mass downwind in some areas, hence the term “rain flight”.

Another process that removes water vapor from the sky is called orographic enhancement or uplift. As the air mass is lifted over our coastal (windward) mountains, it cools and eventually reaches its dew point temperature. When this happens, clouds, rain, sleet, or snow develop on the windward side and ridge of the mountain.

A prime example of this activity is the lush and fertile Sacramento Valley fed by the western slopes of the Sierra Nevada. In contrast, its eastern slopes slope down to the vast Nevada desert as storms move east from the Pacific.

Power cuts for public safety

Wildfire conditions across California have intensified due to rising temperatures and drought conditions.

The combination of dry vegetation and high winds can uproot trees, throw branches over power lines, or create sparks if power lines come into contact with each other. When sparks come into contact with dry vegetation and winds are strong, fires can spread quickly, making them harder to control.

These conditions require power outages for public safety (PSPS). PSPS outages are occurring across the state to prevent wildfires and keep communities safe. For more information, visit

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