Cry Me a River

To most of us, a river is a body of water that runs across the land and usually emanates from another waterway or from melting snow (or other consistent levels of precipitation).  Rivers have names, and while they may shift course every now and again or react to being dammed, we pretty much know where to find them on a map. But as we face strange alterations in precipitation patterns, droughts and floods in new places, it’s time to look at, literally, rivers in the sky, steady tracks of moisture that determine so much of the rain and snow around the globe.

In December of 2013, the American Meteorological Society published Atmospheric Rivers as Drought Busters on the U.S. West Coast byMichael D. Dettinger of the U.S. Geological Survey, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California. Their abstract explains: “Atmospheric rivers (ARs) have, in recent years, been recognized as the cause of the large majority of major floods in rivers all along the U.S. West Coast and as the source of 30%–50% of all precipitation in the same region. The present study surveys the frequency with which ARs have played a critical role as a common cause of the end of droughts on the West Coast. This question was based on the observation that, in most cases, droughts end abruptly as a result of the arrival of an especially wet month or, more exactly, a few very large storms. This observation is documented using both Palmer Drought Severity Index and 6-month Standardized Precipitation Index measures of drought occurrence for climate divisions across the conterminous United States from 1895 to 2010. When the individual storm sequences that contributed most to the wet months that broke historical West Coast droughts from 1950 to 2010 were evaluated, 33%–74% of droughts were broken by the arrival of landfalling AR storms. In the Pacific Northwest, 60%–74% of all persistent drought endings have been brought about by the arrival of AR storms. In California, about 33%–40% of all persistent drought endings have been brought about by landfalling AR storms, with more localized low pressure systems responsible for many of the remaining drought breaks.”

Heating and warming trends in the Pacific Ocean have also impacted precipitation patterns: “El Niño is the warm phase of the El Niño Southern Oscillation (commonly called ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (between approximately the International Date Line and 120°W), including off the Pacific coast of South America. El Niño Southern Oscillation refers to the cycle of warm and cold temperatures, as measured by sea surface temperature, SST, of the tropical central and eastern Pacific Ocean. El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific. The cool phase of ENSO is called ‘La Niña’ with SST in the eastern Pacific below average and air pressures high in the eastern and low in western Pacific. The ENSO cycle, both El Niño and La Niña, causes global changes of both temperatures and rainfall.Mechanisms that cause the oscillation remain under study.” Wikipedia. Low pressure brings rain, high pressure pushed it away.

And unless you have been living in a cave with no media access, you know that the Western United States, particularly California, have been living in a crop-destroying, record-breaking sustained drought, pretty much attribute to global climate change, operating within the cyclical patterns noted above. If only we could prod those rivers or predict their movement, perhaps even direct them where we need water… If… So lots of really smart scientists are beginning to explore that alternative, trying to understand how such rivers in the air grow and move.

“‘These atmospheric rivers — their absence or their presence — really determine whether California is in drought or not and whether floods are going to occur,’ said F. Martin Ralph, a research meteorologist who directs the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography at UC San Diego.

“The storms, which flow like massive rivers in the sky, can carry 15 times as much water as the Mississippi and deliver up to half of the state's annual precipitation between December and February, scientists say. Though atmospheric rivers are unlikely to end California's drought this year, if they bring enough rain to erase the state's huge precipitation deficit, they could wreak havoc by unleashing floods and landslides.

“Scientists using a new type of satellite data discovered atmospheric rivers in the 1990s, and studies since then have revealed the phenomenon's strong influence on California's water supply and extreme weather.

“[In January], a group of government and university scientists, including Ralph, … launch[ed] a major field experiment to better understand atmospheric rivers as they develop over the Pacific. Through the end of February, some researchers will fly airplanes above storms as they pass through, while others will monitor them from ships hundreds of miles off California. As the storms make landfall, the scientists will collect data with ground-based instruments… ‘We're going to measure the heck out of them,’ Ralph said.” Los Angeles Times, January 18^th.

They key is to have a series of aerial rivers, no one too intense, deliver the needed water supply over a reasonable period of time. When too much of a good thing hits, when one of those rivers – our aerial water supply – comes in too suddenly and too fiercely, not only is the water mostly run-off, but the resultant flooding can wreak havoc below. “Ten years ago, an atmospheric river brought record-setting rain to Southern California, causing a mudslide that killed 10 people in the Ventura County beach town of La Conchita.

“Atmospheric rivers are expected to grow stronger over the century as global warming increases the amount of water vapor that can be lifted out of tropical oceans and pushed to higher latitudes… A 2011 simulation by the U.S. Geological Survey found that a hypothetical megastorm — an atmospheric river event so strong it happens only once every 100 to 200 years — could be more catastrophic than a major earthquake, over several weeks bringing 10 feet of rain and hurricane-force winds, widespread flooding, landslides and $300 billion in property damage.” LA Times.

Predicting these events, preparing for them and perhaps learning how to influence their path might go a long way to avoid devastation and enhance a solution for once-productive farmland parched by drought. It is strange that we haven’t paid as much attention to such phenomena as we should have, but this is increasingly an arena to watch develop.

I’m Peter Dekom, and research has never been more needed than it is today… across the board.