Rain for thirsty California

Rain for Thirsty California

December 10, 2014

(This article appeared as a science feature top story on the USGS front page; written largely by CW3E PIs Mike Dettinger and Dan Cayan)

“And it never failed that during the dry years the people forgot about the rich years and during the wet years they lost all memory of the dry years. It was always that way.” —John Steinbeck, East of Eden, 1962

Heavy rains are predicted for California this week, and after the extreme drought of the past few years, California welcomes the moisture. But can there be too much of a good thing?

While drought is a significant natural hazard Californians must contend with, the natural hazards of severe weather and flooding are equally significant in the feast or famine cycle of storms in California.

Current status of atmospheric river approaching the west coast of the U.S. Credit: Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin-Madison

NOAA’s National Weather Service has issued several watches, warnings, and advisories for across California. Flash floods and high winds are expected in many areas.

Drought is a familiar occurrence in California. Indeed, at a year-to-year or shorter time scale, California has a remarkably variable hydroclimate, experiencing larger year-to-year variations in precipitation than anywhere else in the U.S.

In large part, this extreme variability arises from the small number of storms that provide most of the state’s precipitation each year. If a few large storms happen to bypass California in a given winter, precipitation totals are proportionally much reduced and we risk drought. But the wet, drought-busting months are typically reflections of one or two extremely large storms, with almost half of the large drought-busting storms resulting from landfalling atmospheric rivers or “pineapple expresses.”

National Weather Service’s Current Flood Forecast for California rivers. Orange, red and purple dots indicate minor to major flooding. Green dots forecast no flooding.

Atmospheric Rivers (ARs) are constantly moving and evolving pathways of water vapor transport that are thousands of kilometers long but only about 500 km wide and that contain large quantities of water vapor and strong winds They are naturally occurring parts of the global water cycle, responsible for more than 90 percent of all atmospheric vapor transport at latitudes of the conterminous United States. When an AR reaches and encounters mountains in the West Coast states, the fast moving, moisture-laden air contained in ARs generally flows up and over the coastal and Sierra Nevada ranges, leading to almost ideal conditions for producing intense and sustained precipitation. Because of the intensity and persistence of their rains, ARs are the cause of many of the most extreme storms along the West Coast and a large majority of the floods in that region.

The Sacramento, California flood of 1862 was the result of atmospheric river storms.

Atmospheric rivers 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 percent of all precipitation in the same region. In terms of droughts in California, about 33 – 40 percent of all persistent drought endings have been brought about by landfalling AR storms, with more localized low-pressure systems responsible for most of the remaining drought breaks.

In 2010, the USGS Science Applications for Risk Reduction (SAFRR) program created an interdisciplinary scenario about large atmospheric river storms in California called ARkStorm. The ArkStorm scenario brought together experts in climate, weather, economics, geography, and other disciplines to create a hypothetical, but scientifically plausible scenario of a future large storm that is providing emergency responders, resource managers, and the public with a realistic example that they can use to determine the possible consequences of a really large AR storm might be.

A new Center at UC San Diego’s Scripps Institution of Oceanography has established a regional effort on atmospheric rivers and other types of extreme weather and water events in the Western U.S. The Center for Western Weather and Water Extremes (CW3E) is developing an “AR Portal” with partners across the nation, including NOAA, California Department of Water Resources, Plymouth State University, and the USGS. The portal brings together advances in AR science, monitoring and prediction, and builds heavily on data from the new AR monitoring network installed across California, and takes unique advantage of existing USGS, NOAA and other monitoring and prediction systems by developing tools tailored to the AR phenomenon.

Flooding in the Pacific Northwest: R-CAT 2 event

Flooding in the Pacific Northwest: R-CAT 2 event

November 30, 2014

Pacific Northwest Flooding (slide 3; M. Ralph and L. Schick)

CW3E director Marty Ralph and US Army Corps of Engineers researcher Larry Schick provide a summary of recent flooding in the Pacific Northwest. The heavy precipitation (ending November 28) resulted in an R-CAT 2 event (an event which produces 12-16 inches of precipitation in a 3-day period).

During this event one can see an orographic enhancement of precipitation amounts with a rain “shadow” (low amounts of precipitation) in the Seattle region (slide 2). The heavy precipitation resulted in several streamflow sites exceeding flood stage (shown above; slide 3). The Northwest River Forecast Center had an excellent forecast of peak flow on the Skagit River (slide 4).

(Please click here for powerpoint slides)

The attached ppt includes a summary of flood operations in general and at the sites on the Skagit River and near Mt. Rainier.

Forecasts are from the Northwest River Forecast Center (NWRFC): click here for water supply forecasts.

Forecasts are also from the weather service forecast office of the National Weather Service in Seattle: please click here.

Short diagnosis of development of a tropic surge, cut-off low and AR features

Short diagnosis of development of a tropic surge, cut-off low and AR features

December 2, 2014

Storm surge summary (slide 10; M. Ralph)

CW3E director Marty Ralph provides a short diagnosis of an interesting case with a variety of features coming together to generate very large IWV in this currently landfalling storm.

Dr. Ralph notes “This could be a useful event to diagnose more deeply given its relevance to many things we are working on, and the debates about AR, cut-off low, tropical moisture exports, etc. The IVT perspective needs to be explored as well, but the IWV features are quite telling. Jay Cordeira had shared a brief synopsis including a cross-section from GFS that showed the vapor transport over LA maximized at about 3.5 km, which may be more like a ‘tropical moisture export’ structure (Knippertz et al).”

(Please click here for powerpoint slides)

The attached ppt includes an isochrone analysis of the northern edge of the tropical water vapor reservoir (using 4 cm IWV – summary shown above and in slide 10) and its landfall (as seen in the GPS-Met network – slide 11). Also, the snow levels are well-observed with the new SLR network and shows strong north-south variation (slide 12)..

Forecasts are available from the California Nevada River Forecast Center (CNRFC): click here for precipitation forecasts..

Forecasts are also available from the weather service forecast office of the National Weather Service in San Diego: please click here.

CalWater-ACAPEX 2015 Planning Workshop

CalWater-ACAPEX 2015 Planning Workshop

Scripps Institution of Oceanography

La Jolla, California

CalWater 2 Co-Leads: Marty Ralph, Kim Prather, Dan Cayan (Scripps)

Organizing Committee: Chris Fairall (NOAA), Ruby Leung (PNNL), Andrew Martin (Scripps), Ryan Spackman (NOAA/STC)

CalWater2 – ACAPEX Observational Strategy Winter 2014-15

CalWater-2 took major steps from vision to reality on 22-24 April 2014 at Scripps Institution of Oceanography when roughly 40 key individuals (scientists, engineers, aircraft and ship managers, and students) met to plan for major field deployments in 2015. The following facilities are committed (or nearly so) to a field campaign between roughly 10 January and 10 March 2015:

  • DOE – G-1 aircraft
  • DOE AMF-2 ocean-atmosphere facility on the NOAA Research Vessel (ship) Ron Brown
  • NOAA G-IV aircraft
  • NOAA P-3 aircraft
  • ATOFMS mobile, land-based aerosol-sensor suite
  • EFREP hydrometeorological Mesonetwork in California

The DOE facilities are part of the ARM Cloud Aerosol Precipitation Experiment (ACAPEX) experiment addressing (1) aerosol impacts on clouds and precipitation and (2) atmospheric rivers. The NOAA facilities were requested also based on the CalWater vision, with an emphasis on atmospheric-river science questions.

The workshop concluded with a plan for specific start and end dates for each facility, narrowed options for where to operate them, a plan for a field operations center (and a specific possible location), strategies for developing coordinated ship and aircraft operations, and plans for the forecasting capabilities needed to guide missions. In addition, the 12-member CalWater Core Scientific Steering Group met afterword and reviewed plans for 2016-2018 and strategies to advance the longer term Calwater Vision. The Steering Group committed to organizing two special sessions and a side meeting (for last minute coordinations of the 2015 CalWater and ACAPEX activities) at the Fall Meeting of AGU in December 2014, and a journal article describing the program. The proposed AGU sessions are:

  1. CalWater Theme 1: Cloud-Aerosol-Precipitation Interactions in California (Conveners: Daniel Rosenfeld, Kimberly Prather),
  2. Atmospheric Rivers: Observations, Dynamics, Modeling, Impacts and Applications (Conveners: Marty Ralph, Duane Waliser, Jason Cordeira).

The presentations from the Workshop are available here.

Workshop Sponsored by:

  • Scripps, Center for Western Weather and Water Extremes (CW3E)
  • Scripps Center for Aerosol Impacts on Climate and the Environment (CAICE)
  • Science and Technology Corporation (STC)

Workshop Sponsored by:Workshop Participants

Photo of most workshop participants at the CalWater 2015 – ACAPEX workshop at Scripps, April 2014.

CalWater2 Workshop Participants

ARs Play Role in Greenland Melt Episodes

Atmospheric Rivers Play Key Role in Rare Greenland Melt Episodes

Integrated Water Vapor (IWV) impacting Greenland on July 9, 2012 based on data from the 20th Century Reanalysis.

Researchers at NOAA’s Earth System Research Laboratory and the Center for Western Weather and Water Extremes here at Scripps have published a new article examining the processes responsible for the unusual melting episode in Greenland during the summer of 2012 when temperatures at the summit of Greenland rose above freezing for the first time since 1889. They found a number of climate factors were present in both 1889 and 2012 including strong atmospheric rivers transporting warm, moist air towards Greenland’s west coast. The research article was published in the Journal of Geophysical Research – Atmospheres.

A more in depth news story on this research can be found on the Scripps website.

A personal use copy of the article is available here.

Vision for future observations of extreme events in Western US

Vision for Future Observations of Extreme Precipitation and Flooding in the Western U.S.

A journal article entitled: A Vision for Future Observations for Western U.S. Extreme Precipitation and Flooding, by CW3E Director F. Martin Ralph and colleagues was recently published in the April 2014 issue of the Journal of Contemporary Water Research and Education

The paper describes how new technologies and paradigms using the most recent technological and scientific advances can be used to better monitor and predict extreme storms that lead to flooding in the Western U.S. The strategy is intended to add new technology to existing observational networks rather than replacement. The full journal article can be accessed here.

Schematic network of new sensors (land-based) to improve monitoring, prediction, and climate trend detection for hydrometeorological conditions that create extreme precipitation and flooding.

Atmospheric Rivers as Drought Busters

Atmospheric Rivers: Drought Busters

Drought status in California before and after two atmospheric river events in January 2010 (middle panel shows precipitation from these systems over 20 inches in some areas).

Climate.gov recently highlighted CW3E researcher Mike Dettinger’s work looking at atmospheric rivers as drought busters (click here to see the climate.gov post). Mike’s article “Atmospheric Rivers as Drought Busters on the US West Coast” was published in December 2013 in the AMS Journal of Hydrometeorology (find a link to this article on the CW3E publications page or click here). Given the dry conditions that have persisted over the last few years causing severe to extreme drought over the US West this article has received well-deserved attention. The climate.gov piece highlights the impact of an atmospheric river storm from January of 2010. This image (shown above) illustrates the drought conditions before the storm (left panel), the amount of precipitation from the storm (middle panel – showing some areas had over 20 inches of precipitation!) and the drought conditions after the storm (right panel – showing the moderate and severe drought region greatly reduced).

Likelihood of Drought Ending, updated

Drought Recovery by end of Water Year?

The most recent figures can be found on Mike Dettinger’s web page.

Drought Recovery Odds

Updated March 21, 2014

Researcher Mike Dettinger has updated his analysis examining the likelihood of the California drought ending by the end of the current water year on Sept 30, 2014. This new analysis utilizes the just released February precipitation totals for California’s climatic divisions as well as best guess estimates for March 2014 precipitation. Visit the CW3E Drought Info Page to see updated projections for all seven of California’s climatic divisions.

Drought Recovery Odds

February 12, 2014

CW3E researcher Mike Dettinger was interested in knowing the likelihood of California recovering from the drought by the end of the current water year on Sept 30, 2014. The method he came up with starts with the precipitation deficit from last water year (Oct 2012 – Sept 2013). Observed precipitation for Oct 2013 thru Jan 2014 was used to determine what has been added to this previous water year deficit, depicted in the above figure by the black squares. Here negative precipitation refers to the carryover deficit from the period extending back to October 2012.

Projections into the future of cumulative precipitation since Oct 2012 were computed by adding observed monthly precipitation from each year in the historical record, 1931-2013, or a total of 83 projections. For each future month (Feb-Sep 2014) the red dots in the above figure represent each of the 83 projections.

The example shown above is for the Sacramento Drainage region (CA Climate Division 2). For this region, only 2 of the 83 projections make it above the 75%-tile level by the end of Sept 2014. None of the projections show the 24-month cumulative precipitation reaching “normal” levels by the end of this water year.

Visit the CW3E Drought Info Page to see projections for all seven of California’s climatic divisions.

Scripps Researchers Take Flight

Scripps and NOAA Researchers Take Flight to Observe Atmospheric River

IWV Feb 5-10, 2014

Integrated Water Vapor GFS Analysis Feb 5-10, 2014.

Researchers from Scripps Institution of Oceanography at UC San Diego, and NOAA are taking part in research flights to observe a distinctive type of storm system that has historically provided significant precipitation to California.

Scientists tracked the evolution of “atmospheric rivers,” narrow corridors of strong water vapor transport that can extend thousands of miles, as they made landfall in central California in early February. Atmospheric rivers (ARs), identified by researchers only in recent decades, can provide beneficial water supply and snowpack to the West Coast as well as create conditions for dangerous floods that affect lives and property. NOAA, Scripps, USGS, and other agency/institution researchers, working with water managers for the state, Sonoma County, and elsewhere, are studying them with the goal of providing better information for earlier and more accurate extreme weather forecasts. Scripps and USGS scientists are also looking at how atmospheric rivers may serve as “drought busters” and how climate change may affect atmospheric rivers in future decades.

Scripps researchers said that the February storms provided some relief, but would likely not reverse the dangerous drought conditions throughout California and the West that have built up over the last three years.

“Part of the reason for the drought has been the absence of atmospheric river storms hitting the region over the last year,” said Scripps climate researcher Marty Ralph. “From Feb. 7-10, a series of modest strength ARs hit Northern California, including near San Francisco and the northern Sierra where AR conditions stalled for up to 48 hours. These conditions created up to 12-15 inches of rain in three days, including in areas hit by the drought. This was more than double the precipitation in Northern California that had fallen in the first four months of the normal wet season. Nonetheless, the extreme drought has produced such a deficit in water that the soils absorbed much of the precipitation and rivers quickly receded to levels that are again well below normal, even though they reached fairly high levels during the storm.”

Ralph heads the Center for Western Water and Weather Extremes (CW3E), a new center established at Scripps Oceanography that is devoted to California’s special precipitation characteristics. At the core of the center will be a unique advanced network of monitoring stations throughout the state to help industries and 38 million California residents understand phenomena that affect the economy and everyday life in myriad ways.

The network, built over the last five years by NOAA and Scripps through support from California’s Department of Water Resources, will initially contain four atmospheric river observatories, monitoring stations located in Northern and central California that measure amounts of water vapor in the atmosphere and other climate variables.

“NOAA is very interested in improving our forecasts of extreme weather events, and atmospheric rivers rank with hurricanes as a major issue,” said Chris Fairall, chief of the Weather and Climate Physics branch of NOAA’s Earth System Research Laboratory in Boulder, Colo. “The West Coast relies on them for water, but it really is like trying to drink from the proverbial firehose. This new research collaboration on atmospheric rivers with Scripps and UC San Diego is a big step in attacking the problem.”

For this event, Ralph, Fairall, and colleagues gathered data aboard a NOAA Gulfstream IV aircraft that began flying over the Pacific Ocean off the U.S. West Coast on Feb. 7. During the flights, researchers measured several atmospheric properties at several locations along and across the atmospheric river corridor to better understand key processes, such as where the water vapor sources are and how they are sustained by storm dynamics.

Aboard the aircraft, researchers released small parachuted devices, called dropsondes, across the atmospheric river over the Pacific Ocean. As they descend, the dropsondes measure atmospheric conditions, such as pressure, temperature, humidity, wind speed and direction, and transmit the information back to the aircraft where a flight scientist uses it to guide the mission. After the dropsonde data are analyzed and processed, the information will be put into a standard format established by the World Meteorological Organization and provided to NOAA’s National Hurricane Center for inclusion in global and local-scale weather prediction models.

Mike Dettinger, a CW3E team member and research hydrologist with Scripps and the U.S. Geological Survey, noted that atmospheric rivers provide 30 to 50 percent of the precipitation in California and are behind 80 percent of the floodplain inundations along parts of the Central Valley where those inundations are a necessary part of ecosystem food webs and fish nurseries. They figure prominently in the ending of California droughts but also in taxing Northern California levees and other components of the state’s water delivery infrastructure.

“Thus, better understanding of how atmospheric rivers work and how they may change in the future is critical to better water, floods, and ecosystem management and to plans for adapting to future climate changes,” Dettinger said.

Jay Jasperse, chief engineer for the Sonoma County Water Agency, which provides water to 600,000 people and many agricultural users, said of the February storms, “although this AR may not be the strongest ever, it is certainly the most welcome.”

Results from this study will help guide atmospheric river research for the upcoming CalWater 2 experiment, which begins in 2015 and will use land-based stations and a research ship as well as multiple aircraft.