Rivers of water in the air provide much of California’s rain

Atmospheric rivers are bands of warm temperatures and strong winds that push large amounts of water vapor, often for thousands of miles. Scientists from government and university research institutions have deployed a force of research aircraft and an oceangoing vessel to better understand the phenomenon and how it results in precipitation for California.

Scientists said that too little is known about atmospheric rivers and that better understanding would aid meteorologists’ ability to predict weather.

“We don’t understand enough about how atmospheric rivers transport water vapor and how the water vapor comes together in them. We also don’t know enough about how aerosols can change the amount of precipitation that can come out of an atmospheric river when it hits shore,” said Marty Ralph, a research meteorologist and director of the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography.

The need to understand atmospheric rivers is made apparent by the realization of how much water vapor exists in one at a given time. Ralph said that early estimates of the water vapor in atmospheric rivers put the equivalent at 10 times the amount of water emptied into the Gulf of Mexico by the Mississippi River. He said refined estimates have put that amount even higher.

“We had thought it was 10 Mississippis, as an average value for atmospheric rivers, but the average of cases we have now is 20 Mississippis,” Ralph said. “A handful of atmospheric rivers each year, provide about 30-50 percent of all the precipitation in Northern California.”

Over the next month, four research aircraft from the National Oceanic and Atmospheric Administration, the Department of Energy and NASA will fly into atmospheric rivers hundreds of miles off the coast of California, taking a host of readings. A NOAA ship will also take measurements as part of the coordinated effort.

“This experiment will double the number of samples we have, so we’ll have a much more accurate measure of how strong the atmospheric rivers are,” Ralph said.

Among other things, the project, titled CalWater 2015, will explore the role of air particles, natural or human induced, in precipitation from atmospheric rivers. Research has indicated that some pollution may inhibit precipitation by keeping large water droplets from forming at the bottoms of clouds. However, researchers said more work needs to be done to better understand potential human impacts on rain and snowfall.

“We are only scratching the surface in terms of how aerosols influence the precipitation, because aerosols are of so many different types and so many different sizes,” said Ryan Spackman, flight operations scientist for CalWater 2015. “Every single water droplet or ice crystal, for instance snow, that falls from the sky has an aerosol particle at its center, so aerosols are key to understanding how much is going to fall, where it’s going to fall, how distributed the precipitation is, which is crucial for water supply understanding.”

Spackman said better understanding will allow water managers to anticipate where and when precipitation will fall, thus allowing them to make decisions to maximize preparedness.

“In the state of California, there’s tremendous amount of variability in when that precipitation falls. It’s feast or famine, and that’s a very challenging problem for water managers – how much water to keep, when to let it go, and are we going to have enough,” Spackman said. “This research is aimed at improving our abilities to forecast these events.”

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The 10 Most Important Water Stories in 2014

1. The California Drought Becomes an Emergency
California’s multi-year drought grew dire enough in 2014 to prompt Governor Jerry Brown to declare a drought emergency in January. By the end of the year, California had experienced the driest and hottest 36 months in its 119-year instrumental record. Some researchers described the drought as 1) the worst in over 1200 years and 2) evidence of rising temperatures globally as climate changes accelerate. As of mid-January, the drought is continuing.

2. Tigris and Euphrates River Dams Influence Islamic State Expansion
Conflicts over water have a long history. In 2014, a new analysis described the links between drought, climate change, water management, and the Syrian civil war. By the end of the year, the region’s major dams were targeted for control by the Islamic State (IS) and used as weapons to flood parts of Iraq and to divert water away from some communities for political purposes. IS forces near these dams were also targets of allied air strikes because of the dams’ strategic importance.

3. U.S.-China Climate Agreement Includes Water-Energy Provisions
On November 12, 2014, the President of the United States reached a momentous accord with the President of China to cap greenhouse gas emissions and do a whole lot more for Mother Earth and its human inhabitants. The agreement encourages collaboration between the world’s two largest economies to much more quickly put into place new tools, practices, and especially markets to contend with radically different ecological and economic conditions. The agreement includes two provisions to secure freshwater supplies in energy production. The two nations are 1) investing in research to improve efficiency and conservation in water supply for energy generation and 2) developing a carbon-sequestration demonstration project in China to put to good use the water that is displaced from deep beneath the surface during CO2 storage.

4. The U.S. Safe Drinking Water Act Turns 40 Amid Mounting Safety Lapses
In the year that the U.S. Safe Drinking Water Act turned 40, Toledo, Ohio, Charleston, West Virginia, and towns along North Carolina’s Dan River were the victims of pollution incidents that highlighted the continued challenges in safeguarding water supplies and protecting public health. Toledo shut down its water supply after poisonous algae toxins developed in Lake Erie. Charleston’s water supply was fouled by a chemical spill that prompted the Justice Department to indict the plant’s owners for water-quality violations and obstruction of justice. In North Carolina, a storage basin failure at a Duke Energy power plant sent more than 35,000 metric tons of coal ash, a noxious waste product, flowing into the Dan River, a drinking water source.

5. Evidence of the Link between Climate Change and Extreme Hydrologic Events Grows Stronger
The evidence of the links between climate change and extreme hydrologic events grew more powerful in 2014. A series of scientific reports addressed heat waves in Europe, coastal damages in the Eastern United States during extreme tides and storms, flooding in the UK from more intense rain storms, drastic loss of Arctic ice, and droughts in Australia and the Southwestern United States. Lloyd’s of Londonconcluded in May that the influence of rising sea levels increased the damages from Hurricane Sandy by $US 8 billion in New York alone. Sao Paulo, Brazil’s largest city and located close to the water-rich Amazon Basin, suffered its worst drought.

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