CW3E Publication Notice: A 22-Year Climatology of Cool Season Hourly Precipitation Thresholds Conducive to Shallow Landslides in California

CW3E Publication Notice

A 22-Year Climatology of Cool Season Hourly Precipitation Thresholds Conducive to Shallow Landslides in California

July 31, 2018

CW3E collaborator Nina Oakley, along with CW3E director Mary Ralph and others recently published a study in the American Meteorological Society journal, Earth Interactions. The study is titled “A 22-Year Climatology of Cool Season Hourly Precipitation Thresholds Conducive to Shallow Landslides in California” and explores hourly rainfall observations throughout the state through the lens of precipitation as a trigger for shallow landslides.

Storm-triggered shallow landslides are a common hazard in California’s complex terrain. Where they mobilize into debris flows, they can have devastating impacts on life, property, and infrastructure. Most landslide-susceptible slopes require some amount of antecedent precipitation before intense rainfalls may generate the pore pressures thought to trigger shallow landslides. Post-wildfire debris flows, like the 9 January 2018 event in Montecito that claimed 23 lives, can be triggered by a host of other processes that involve direct runoff from hillslopes. All of these types of mass movements require moderate to high intensity rainfalls whose intensities exceed local infiltration rates. Our research is thus relevant to a broad category of geologic processes (landslides, runoff, runoff-generated debris flows, etc.) that threaten California’s welfare. There are implications of this work beyond landslides; results may inform reservoir operations, floodplain management, and public safety.

Historic records of landslide occurrence in California document many events within populated areas such as the San Francisco Bay Area and Transverse Ranges of southern California. There are far fewer records from outside these regions. One hypothesis for the distribution of observed landslides is that some areas of California do not frequently experience rainfall of sufficient intensities and durations to trigger shallow landslides. We tested this hypothesis by documenting where hourly rainfall in the cool season (October-May) in California met or exceeded published values thought to trigger landslides after a seasonal antecedent precipitation threshold has been met. The thresholds examined were 5, 10, 15 and 20 mm h-1 as well as 7.5 mm h-1 for 3h, and 5 mm h-1 for 6h. We also evaluated the relationship between these events and atmospheric rivers.

We develop an hourly precipitation data set for this analysis by applying quality control to a 147 Remote Automated Weather Stations (RAWS; across California over a 22-year period. Our analysis shows that stations with exposure to southerly atmospheric flow in the Coast and Transverse Ranges experience high numbers of over-threshold events at all intervals, coincident with areas with the greatest number of observed landslides. Our results also highlight areas where over threshold events frequently occur but landslide observations are lacking; one such region is the northwestern Sierra Nevada. In the regions experiencing the highest number of over-threshold events, approximately 60-90% (depending on threshold examined) are associated with atmospheric rivers. The number of over threshold events varies greatly both within a season and inter-annually, though the greatest frequency tends to coincide with the climatological wettest month of the year. Individual storm events commonly It is feature multiple over-threshold events, especially at lower intensities or multi-hour thresholds.

Our study brings together atmospheric scientists and geologists. Co-authors include Jeremy Lancaster and Stefani Lukashov from the California Geological Survey, Ben Hatchett and Shawn Roj form the Desert Research Institute/Western Regional Climate Center, and John Stock from the US Geological Survey. This study was supported by the California Department of Water Resources, the National Oceanic and Atmospheric Administration’s Climate Program Office through the California Nevada Applications Program, and the National Aeronautics and Space Administration through the Nevada NASA Space Grant Consortium.

Landslide observations and frequency of intense precipitation. Left: Shallow landslides compiled by the California Geological Survey are shown as black dots. Geomorphic provinces are overlain on the map. The four provinces most pertinent to the study are labeled. Right: Marker size indicates the number of precipitation events exceeding 15 mm h-1 during the October-May period 1995-2015 at each RAWS station. Marker color indicates the percentage of total 15 mm h-1 events associated with atmospheric river conditions.

Oakley, N.S., J.T. Lancaster, B.J. Hatchett, J. Stock, F.M. Ralph, S. Roj, and S. Lukashov, 2018: A 22-Year Climatology of Cool Season Hourly Precipitation Thresholds Conducive to Shallow Landslides in California. Earth Interact., 22, 1–35, ,

CW3E Attends MPAS Tutorial at NCAR

CW3E Attends MPAS Tutorial at NCAR

July 30, 2018

CW3E’s Rachel Weihs, Minghua Zheng, and Caroline Papadopolous had the pleasure of attending the Model for Prediction Across Scales (MPAS) tutorial workshop at National Center for Atmospheric Research’s (NCAR) facility in Boulder, CO. MPAS represents the next generation of regional and global variational-scale weather prediction models and was developed at NCAR. While its main parameterization packages (e.g. radiation, planetary boundary layer, microphyiscs schemes) are imported from the Weather Research and Forecasting (WRF) model, it utilizes a new grid structure and cell interaction framework (called unstructured Voronoi meshes and C-grid discretization, respectively) to compute diagnostic and prognostic dynamics.

Led by prominent numerical weather prediction experts Bill Skamarock, Michael Duda, and Wei Wang, the tutorial was a combination of hands-on and theoretical training on the model. During the two-day workshop, scientists from CW3E learned how to operate and configure the model in a test-bed environment and successfully produced an experimental atmospheric river forecast focused on Northern California. The training received at the workshop will be instrumental to CW3E’s future modeling developments in response to an ever-evolving and technologically-advancing industry.

CW3E’s Minghua Zheng outside of the National Center for Atmospheric Research at the Model for Prediction Across Scales (MPAS) tutorial workshop held in Boulder, CO July 2018.

CW3E Presents at UCSD’s U.S.-China Future Leaders Summer Program

CW3E Presents at UCSD’s U.S.-China Future Leaders Summer Program

July 26, 2018

CW3E’s Anna Wilson recently gave a presentation introducing the center to high school students attending the U.S.-China Future Leaders Summer Program. This program, held at UCSD’s School of Global Policy and Strategy, was co-run by the School’s 21st Century China Center and the Global Leadership Institute, and led by award-winning high school teacher Kristen Druker. The program design is meant to foster problem-solving and decision-making skills, critical thinking about global policy issues and diplomacy and conflict resolution techniques. The students participate in game-based role-playing focused on global challenges that concern the U.S. and China, particularly on the topics of clean energy and climate change.

Hearing about how CW3E is working to reach our goals (to revolutionize the physical understanding, observations, weather predictions, seasonal outlooks and climate projections of extreme events in Western North America, including atmospheric rivers, the North American summer monsoon and their impacts on floods, droughts, hydropower, ecosystems, and the economy) reinforced the lessons they are learning in the curriculum. The CW3E presentation focused on several core areas of the center: atmospheric rivers; Forecast Informed Reservoir Operations (FIRO), and climate science. Discussion with the students throughout the presentation dealt with many topics, including policy implications of scientific findings and climate change mitigation and adaptation strategies. CW3E is grateful to have had the opportunity to interact with the intelligent and enthusiastic students.

CW3E Publication Notice: Global Evaluation of Atmospheric River Subseasonal Prediction Skill

CW3E Publication Notice

Global Evaluation of Atmospheric River Subseasonal Prediction Skill

July 26, 2018

CW3E collaborators Michael DeFlorio (NASA/JPL), Duane Waliser (NASA/JPL), and Bin Guan (UCLA), along with CW3E director Marty Ralph and colleague Frederic Vitart of the European Centre for Medium-Range Weather Forecasts (ECMWF), recently published a paper in Climate Dynamics titled Global Evaluation of Atmospheric River Subseasonal Prediction Skill (DeFlorio et al., 2018).

The study uses the number of AR days occurring over a week-long period (Fig 1), to quantify global atmospheric river (AR) prediction skill using Subseasonal to Seasonal (S2S) Project hindcast data from ECMWF. The study found that ECMWF forecast skill is higher than a reference forecast in several subtropical and midlatitude regions up to a three-week (15-day to 21-day) lead time. The forecast skill is affected during particular phases of climate mode variability, including the El Niño-Southern Oscillation, Arctic Oscillation, Pacific-North America teleconnection pattern, and Madden-Julian Oscillation (Fig 2). In particular, forecast skill is generally improved at week two during MJO Phase 8 conditions. The results highlighted in this paper provide information to support improved subseasonal forecasts.

Figure 1. Figure (1a-d) from DeFlorio et al. (2018): Global climatology of atmospheric river (AR) occurrence (number of AR days per week; hereafter AR1wk occurrence) for ERA-I and ECMWF in November-December-January-February-March (NDJFM; a,c) and May-June-July-August-September (MJJAS; b,d) during the period 1996-2015. The week-1 (0d-6d) lead time forecast window is chosen. Blue rectangles in a) denote area-averaged regions selected for analyses in subsequent figures.

Figure 2. Figure (13a,b) from DeFlorio et al. (2018): Composite forecast skill of AR1wk occurrence (number of AR days per week) anomalies during particular MJO phases (red) over the North Pacific/Western US regions in NDJFM during the period 1996–2015. Mode and region combinations with large (~ 95% confidence) skill differences between particular MJO phases and the all-days case are shown. Red and black horizontal lines represent 95 and 5% quantile values for a bootstrapped distribution of the particular MJO phase and all days case, respectively, re-sampled 1000 times with replacement.

DeFlorio, M., D. Waliser, B. Guan, F.M. Ralph, and F. Vitart, 2018: Global evaluation of atmospheric river subseasonal prediction skill. Climate Dynamics, early online release,

CW3E Graduate Student Serves as GELS Instructor

CW3E Graduate Student Serves as GELS Instructor

July 18, 2018

This summer, CW3E graduate student Kara Voss served as a science instructor for the Global Environmental Leadership & Sustainability (GELS) Scripps/Washington D.C. program. In this two-week program, high achieving high school students come to SIO to learn the basics of oceanographic and atmospheric data collection and interpretation, in addition to leadership skills. Then, they travel to Washington D.C. along with the instructors to meet with the Congressional Representatives of their home districts and advocate for science-based environmental policies of the student’s choice.

The GELS group on the steps of the Capitol Building.

CW3E graduate student Kara Voss (left) leading students to their meetings with their representatives.

CW3E Graduate Student Selected to Participate in the 9th International High Performance Computing Summer School

CW3E Graduate Student Selected to Participate in the 9th International High Performance Computing Summer School

July 17, 2018

CW3E’s Meredith Fish was one of 80 graduate students and postdoctoral scholars selected to participate in the 9th International High Performance Computing Summer School in Ostrava, Czech Republic, which was held from 8-13 July 2018 at the IT4Innovations National Supercomputing Center. The school was sponsored by the Extreme Science and Engineering Discovery Environment (XSEDE), the Partnership for Advanced Computing in Europe (PRACE), the SciNet High Performance Computing (HPC) Consortium, and the RIKEN Advanced Institute for Computational Science. There she engaged in lectures and hands-on sessions on a variety of topics, including: HPC challenges, HPC programming proficiencies, performance analysis and profiling, data-intensive computing, data visualization and algorithmic approaches. She also had the opportunity to present her research on atmospheric river families to other HPC users focusing on the technical aspects of her work.

Group photo from the International High Performance Computing Summer School in July 2018

Meredith in front of the Technical University of Ostrava, which is a part of the IT4Innovations National Supercomputing Center.

CW3E Director Honored at California Extreme Precipitation Symposium

CW3E Director Honored at California Extreme Precipitation Symposium

July 10, 2018

The annual California Extreme Precipitation Symposium, a Floodplain Management Association project, was held this year on July 9, 2018 at the University of California, Davis. This year’s theme was Paleoclimate Insights for Planning Future Natural Resources in California. Slides from all presentations are available at:

Each year since 2004, a Special Recognition Award is presented to “highlight and honor the outstanding contributions of individuals and institutions that have supported and advanced the professions of meteorology, flood hydrology, and flood risk management. These professions share the public safety goal of protecting life and property from the ravages of flooding. Together these professionals provide the tools, information, and knowledge essential for forecasting flood events before they occur, estimating potential flood magnitudes and impacts used in designing flood risk reduction projects, and responding to floods when they occur. Each honoree contributed to making the people of California safer from flood events over their many years of service.” This year, that award was given to CW3E’s director, Dr. F. Martin Ralph. More details are available on the California Extreme Precipitation Symposium website:

From left, Gary Estes (CEPSYM Founder), Marty Ralph (CW3E), and Rob Hartman (RKH Consulting Services).

CW3E Publication Notice: Atmospheric River Tracking Method Intercomparison Project (ARTMIP): Project Goals and Experimental Design

CW3E Publication Notice

Atmospheric River Tracking Method Intercomparison Project (ARTMIP): Project Goals and Experimental Design

July 9, 2018

As research has expanded on ARs, new detection algorithms have been developed, and yet no detailed intercomparison has been made. To fill this gap, a grass roots “community” effort was organized to develop an approach to perform such a comparison, which is described in the recently published paper by Shields et al (2018). The community effort is called the Atmospheric River Tracking Method Intercomparison Project “ARTMIP.” It has been organized by a small, ad-hoc, planning committee, co-chaired by Christine Shields (NCAR) and Jon Rutz (NWS and CW3E), with Mike Wehner (DOE/LBNL), Ruby Leung (DOE/PNNL) and F. Martin Ralph (UCSD/SIO/CW3E) as its members. This team organized its first meeting with interested parties in May 2017, which was hosted and sponsored by CW3E at Scripps Institution of Oceanography (SIO).

The paper was published in Geoscientific Model Development and titled Atmospheric River Tracking Method Intercomparison Project (ARTMIP): Project Goals and Experimental Design ( This paper describes ARTMIP, an international community effort to understand and quantify the uncertainties in atmospheric river (AR) science due to the differences in detection algorithms. The goal of ARTMIP is to provide the weather forecasting and climate community with a deeper understanding of AR tracking, mechanisms, and impacts, through providing a framework with which to objectively compare detection schemes that can be fundamentally different. The paper describes the experimental design and timeline, and includes preliminary results that use the key metrics of frequency, intensity, duration, and precipitation attribution (For an example of preliminary results, see figure 1).

The project is divided into two tiers with different science objectives. The first tier consists of applying all participating algorithms to a common dataset, the MERRA-2 reanalysis, from 1980-2017. The second tier will be divided into subtopics and consist of sensitivity studies to different reanalysis datasets and to climate model data. A variety of precipitation datasets will also be used to assess uncertainties in AR impacts.

The ARTMIP project has been positively received by the AR community and has the potential to shape much of how AR science and detection is conducted. The project has steadily increased participation since the paper was first presented in the open-forum GMD Discussions. Participation in ARTMIP is open to any researchers with an AR detection algorithm or with interest in evaluating the data. If you are interested in participating, please contact Christine Shields ( or Jon Rutz (

Figure 1. Composite MERRA-2 IVT (kg m-1s-1) for landfalling ARs along North American west coast for 14 different algorithms. Time instances where an AR was detected along the coastline were composited for the entire region. Composite data is plotted for February 2017. To test the ARTMIP framework, a 1-month proof-of-concept trial was designed and performed for February 2017. This month was chosen due to large number of landfalling ARs that impacted western North America during this period.

Shields, C. A., Rutz, J. J., Leung, L.-Y., Ralph, F. M., Wehner, M., Kawzenuk, B., Lora, J. M., McClenny, E., Osborne, T., Payne, A. E., Ullrich, P., Gershunov, A., Goldenson, N., Guan, B., Qian, Y., Ramos, A. M., Sarangi, C., Sellars, S., Gorodetskaya, I., Kashinath, K., Kurlin, V., Mahoney, K., Muszynski, G., Pierce, R., Subramanian, A. C., Tome, R., Waliser, D., Walton, D., Wick, G., Wilson, A., Lavers, D., Prabhat, Collow, A., Krishnan, H., Magnusdottir, G., and Nguyen, P., 2018: Atmospheric River Tracking Method Intercomparison Project (ARTMIP): Project Goals and Experimental Design, Geosci. Model Dev.,

CW3E Hosts Student Workshop on AR Forecasting

CW3E Hosts Student Workshop on AR Forecasting

July 2, 2018

On Friday, June 29th, immediately following the 2018 International Atmospheric River Conference (IARC), students from over a dozen educational institutions within and outside of the United States gathered at Scripps to learn from the experts about AR forecasting. The goals of the workshop were to bring students together with AR scientists and forecasters to gain hands-on experience with predictions focused on practical and scientific applications. Outcomes for participants included improved understanding of modern AR prediction tools and methods, and how AR forecasting support selected examples of decision making.

Students first participated in an interactive lecture on AR predictions led by science leadership from the National Weather Service (NWS), the San Diego Swift Water Rescue Team, and CW3E, learning not only about the details of forecasting impacts of an AR but also about communication of risks to local stakeholders (Picture 1). Each student was provided with a NWS forecasting presentation that had previously been used to inform local stakeholders during a real event. The students were then given the task of providing an informed plan, from the standpoint of the local stakeholders, to mitigate the dangers associated to the AR event. This portion of the workshop highlighted the intricacies and difficulties that go into making forecast-informed decisions affecting local decisionmakers and municipalities and the importance of accurate forecasting tools.

Following this interactive lecture, students had the opportunity to use CW3E’s AR forecasting tools to try their hand at planning their own AR Recon airborne and on-the-ground field campaign. This portion of the workshop equipped students with an operational perspective on the AR Recon field campaign and difficulties associated with organizing a large-scale field campaign. Day two of the workshop began with a morning radiosonde balloon launch from the Scripps Pier (Picture 3), followed by a tour of the NWS San Diego forecast office. The NWS tour presented even more information on the operational side of forecasting and highlighted the ways that modern forecasts are communicated to local stakeholders. Students left the workshop eager for the next AR season when they’ll be able to test their skills in real-time! The student forecasting workshop was a great success and is being expanded next year to a colloquium covering all aspects of AR science in greater detail.

Just before releasing a radiosonde at Scripps Pier, workshop participants pose for a photo.

CW3E Publication Notice: The Role of Atmospheric Rivers in Extratropical and Polar Hydroclimate

CW3E Publication Notice

The Role of Atmospheric Rivers in Extratropical and Polar Hydroclimate

June 28, 2018

Deanna Nash (UC Santa Barbara) and CW3E collaborators Bin Guan (UCLA), Duane Waliser (NASA/JPL), along with CW3E director Marty Ralph and Hengchun Ye (Cal State LA) recently published a paper in Journal of Geophysical Research: Atmospheres, titled The Role of Atmospheric Rivers in Extratropical and Polar Hydroclimate.

Atmospheric Rivers (ARs) are narrow, long, transient, water vapor rich corridors of the atmosphere that are responsible for over 90% of the poleward water vapor transport in and across mid-latitudes. However, the role of ARs in modulating extratropical and polar hydroclimate features (e.g. water vapor content, precipitation) has not been fully studied, even though moistening of the polar atmosphere is both a key result of, and amplifier of, arctic warming and sea ice melt, and precipitation is key to the surface mass balance of polar sea ice and ice sheets. This study uses the MERRA2 reanalysis to characterize the roles of AR water vapor transport on the column-integrated atmospheric water vapor budget in the extratropical and polar regions of both hemispheres.

Meridional water vapor transport by ARs across a given latitude (examined for 40°, 50°, 60°, and 70°) is strongly related to variations in area-average (i.e. over the “cap” poleward of the given latitude) total water vapor storage and precipitation poleward of that latitude. For the climatological annual cycle, both AR transport (i.e., non-local sources) and total evaporation (i.e., local sources) are most correlated with total precipitation, although with slightly different phases. However, for monthly anomalies, the water budget at higher latitudes is largely dominated by the relationship between AR transport and precipitation. For pentad and daily anomalies, AR transport is related to both precipitation and water vapor storage variations. These results demonstrate the important role of episodic, extreme water vapor transports by ARs in modulating extratropical and polar hydroclimate.

Figure 1 from Nash et al. 2018. a) A schematic of the atmospheric water budget for a region poleward of a given latitude (e.g. 60ºN). The red arrows indicate flux of integrated water vapor transport (IVT), the majority of which is AR-related in the mid to high latitudes. The green arrows indicate the surface evaporation (E) of water poleward of a given latitude, and the clouds and rain indicate the loss of water vapor when it condenses and falls as precipitation (P). All these terms combine into equation 1 where the change in water vapor storage (∂IWV/∂t) is equal to the evaporation minus the precipitation in the region plus the flux of IVT into that region. b) A schematic showing a top down view of IVT and AR-IVT flux at 60°N. The majority of IVT and AR-IVT enter the Arctic via the red line regions (i.e. the AR-IVT Atlantic and Pacific Pathways).

Figure 10 from Nash et al., 2018. Correlation Ellipses between IVT and each variable (solid ellipse), and AR-IVT and each variable (translucent ellipse). The color of each ellipse indicates the correlation coefficient. The width of each ellipse is 1- |r|, and the orientation (downward/upward) indicates the sign of the relationship (positive/negative). The length of each ellipse is 1 (such that a circle would indicate zero correlation).

This research was supported by the NASA Energy and Water cycle Study (NEWS) program, NASA NCA, and NASA MIRO grant. Deanna Nash’s contribution to this study was made possible by NASA Jet Propulsion Laboratory’s Year-Round Internship Program during her graduate studies at California State University, Los Angeles. Please contact Duane Waliser at with inquiries.

Nash, D., Waliser, D., Guan, B., Ye, H., & Ralph, M. (2018). The Role of Atmospheric Rivers in Extratropical and Polar Hydroclimate. Journal of Geophysical Research: Atmospheres, 123.

2nd International Atmospheric Rivers Conference, June 2-28, 2018

2nd International Atmospheric Rivers Conference, June 25-28, 2018

June 22, 2018

The Center for Western Weather and Water Extremes (CW3E), at the Scripps Institution of Oceanography (SIO), UC San Diego, is hosting the 2nd International Atmospheric Rivers Conference (IARC) from June 25-28, 2018. Ths conference is organized by an international committee, with co-chairs from NASA’s Jet Propulsion Laboratory, the US Army Corps of Engineers, CW3E, and the University of Lisbon.

The conference is located at the seaside Robert Paine Scripps Forum for Science, Society, and the Environment on SIO’s campus. Over 100 experts across multiple fields are coming together to advance the state of the science and explore needs for new information. Fifteen student scholarships were given to students coming from locations such as India, Chile, and across the U.S. There will be extensive opportunity for interaction during the conference and after. A cocktail hour and dinner, included with registration, will be provided on Tuesday, June 26.

The agenda and other information can be found on the IARC website. Traditional oral and poster sessions are combined with panel discussions and breakout sessions. Sessions will be focused on various topics including: Winter 2016-2017; Airborne observations of atmospheric rivers (ARs); Subseasonal to seasonal forecasting of ARs; Applications and communications; AR Tracking; Regional perspectives on ARs; AR dynamics; AR microphysics, aerosols, and chemistry; Weather forecasting of ARs; ARs and Hydrologic Impacts; ARs and climate variability: past, present, and future; and Emerging directions.

Immediately after the conference, CW3E is also sponsoring a student forecasting workshop to be held June 29-30, with exercises planned on decision maker communication and forecasting for airborne field campaigns. Students will also be able to tour the National Weather Service San Diego offices and participate in a demonstration radiosonde launch from the Scripps Pier.

CW3E Graduate Student Attends the American Meteorological Society Summer Policy Colloquium

CW3E Graduate Student Attends the American Meteorological Society Summer Policy Colloquium

June 12, 2018

Colloquium participants visiting the Capitol in Washington, D.C. (Photo credit: AMS)

CW3E graduate student Tashiana Osborne was selected to attend the June 2018 American Meteorological Society (AMS) Summer Policy Colloquium, and was awarded full support by the National Science Foundation (NSF) through a nationwide competition.

During the 10-day AMS Summer Policy Colloquium in Washington, D.C., Tashiana learned from numerous perspectives on how science can inform policy (science-informed policy), and also how policy governs the science we do (policy for science). The colloquium attendees visited the U.S. House of Representatives and the Senate, hearing from senators and House representatives, scientists who transitioned into policy, U.S. intelligence agents (addressing global and national water security), congressional science analysts and staffers, U.S. negotiators, science advocates, registered lobbyists, leaders in private and public sector organizations (focusing on technology, research, development, and implementation), and others.

For one multi-day exercise, small groups were each assigned to act as if representing a particular U.S. senator. Tashiana’s group reviewed a recent carbon tax bill (which, in reality, did not pass into law), negotiated with other “senators”, and eventually proposed amendments to the bill before voting on it. The goal was to take on the views of the assigned senator while considering the unique needs and wants of the constituents they represent. This exercise and others highlighted some of the intricacies and nuances, potential motives, and varying priorities involved in politics. The program also showcased where and how well-communicated scientific information might come into play when it comes to decision-making.

The Summer Policy Colloquium leader, Dr. William (Bill) Hooke, blogged about this year’s program (now in its 18th year!):

Weather, Water and Society on the Colorado River: CW3E Explores the Yampa River Basin

Weather, Water and Society on the Colorado River: CW3E Explores the Yampa River Basin

June 11, 2018

The Yampa River is one of the wildest remaining major tributaries of the Colorado River and supports a rich ecosystem, local agriculture and ranching, and a robust recreation industry. It also provides crucial water supplies to local stakeholders and locations as far removed as Arizona and Southern California. A multitude of environmental and societal needs influence water management and conservation decisions in the Yampa River, and are pertinent to other watersheds around the American West. Similarly, regional weather and climate extremes help shape the basin’s hydrology, environment, and water resources.

This June, CW3E travelled to Steamboat Springs, Colorado, for the Yampa Basin Workshop. This was a community-oriented event organized by CW3E and partners from Colorado Mountain College, Yampa Valley Sustainability Council, Friends of the Yampa, and Wyndham Resorts. During the Workshop, participants examined the Yampa River Basin through the lens of weather, environment, and culture. The workshop included talks by local experts, discussion panels, afternoon field learning, and a community event. After building a foundation on the region’s history and environment, we explored the various demands on the Yampa’s water, and learned how these needs are met and where challenges remain. This dialogue with the local community introduced graduate students, post-doctoral scholars, researchers, staff and faculty from CW3E to the Yampa Basin. Drawing from the community’s historical knowledge and expertise on the challenges and successes of conservation and use practices on the Yampa, the Workshop has prompted new research directions for CW3E that will support weather and water decision-making processes in the Colorado River Basin and California.

CW3E group photo on the Fetcher Ranch, June 7th, 2018. (Pictured left to right, Marty Ralph, Rachel Weihs, Lindsey Jasperse, Anna Wilson, Rob Hartman, Kara Voss, Douglas Alden, Meredith Fish, Brian Kawzenuk, Leah Campbell, Mike Sierks, Will Chapman, Ali Hamidi, Aneesh Subramanian, and Tamara Shulgina). Photo credit: Rachel Weihs

CW3E’s Anna Wilson chairs a panel discussion at the Yampa River Rendezvous at the Colorado Mountain College in Steamboat Springs, CO, June 5th, 2018. Pictured: Mike Meyers (National Weather Service), Jon Rutz (CW3E/NWS Western Region), Gannet Hallar (Storm Peak Lab, U. of Utah), Becky Bolinger (Colorado State University). Photo credit: Rachel Weihs

George Stanko (forefront) talks to the CW3E team on Stanko Ranch near the Yampa River, June 5th, 2018. Photo credit: Rachel Weihs

CW3E Staff Member Attends Russian River Science Forum

CW3E Staff Member Attends Russian River Science Forum

May 03, 2018

CW3E’s Anna Wilson recently attended the Russian River Science Forum, held at the Sonoma County Water Agency on May 1. The Forum was sponsored by the California Land Stewardship Institute, Sonoma County Agricultural Preservation and Open Space District, and Sonoma County Water Agency, and was meant to gather together scientists, conservationists, and stakeholders to discuss research needs and ongoing work being conducted in the watershed. The framework for the forum was research priorities identified by the Russian River Independent Science Review Panel (ISRP). Broadly, these priorities are: aquatic communities; groundwater; streamflow; climate change; water demand and use; geomorphology; and development of a numerical model of the watershed.

Presentations included ongoing relevant weather and climate research conducted by CW3E and partners (Anna Wilson, CW3E), local research applications (Jay Jasperse, Sonoma County Water Agency; Karen Gaffney, Sonoma County Agricultural Preservation and Open Space District), monitoring the effects of the 2017 wildfires (Jonathan Perkins, US Geological Survey; Virginia Mahacek, Sonoma County Office of Recovery and Resilience), and restoration design (Neil Lassettre, Sonoma County Water Agency). There was time for discussion regarding progress on the recommendations from the ISRP, and on future collaborations between interested researchers and stakeholders. CW3E looks forward to further partnerships towards advancing science objectives in the Russian River watershed and assisting in the development of science-based, resilient, and effective watershed management strategies.

CW3E Publication Notice: Global Analysis of Climate Change Projection Effects on Atmospheric Rivers

CW3E Publication Notice

Global Analysis of Climate Change Projection Effects on Atmospheric Rivers

May 24, 2018

Vicky Espinoza (UC Merced) and CW3E collaborators Bin Guan (UCLA), Duane Waliser (NASA/JPL), along with CW3E director Marty Ralph and David Lavers European Centre for Medium‐Range Weather Forecast, recently published a paper in Geophysical Research Letters, titled Global Analysis of Climate Change Projection Effects on Atmospheric Rivers.

Atmospheric rivers (ARs) are elongated strands of horizontal water vapor transport, accounting for over 90% of the poleward water vapor transport across midlatitudes. ARs have important implications for extreme precipitation when they make landfall, particularly along the west coasts of many midlatitude continents (e.g., North America, South America, and West Europe) due to orographic lifting. ARs are important contributors to extreme weather and precipitation events, and while their presence can contribute to beneficial rainfall and snowfall, which can mitigate droughts, they can also lead to flooding and extreme winds. This study takes a uniform, global approach that is used to quantify how ARs change between Coupled Model Intercomparison Project Phase 5 (CMIP5) historical simulations and future projections under the Representative Concentration Pathway (RCP) 4.5 and RCP8.5 warming scenarios globally. The projections indicate that while there will be ~10% fewer ARs in the future, the ARs will be ~25% longer, ~25% wider, and exhibit stronger integrated water vapor transports under RCP8.5 (Figure 1). These changes result in pronounced increases in the frequency (integrated water vapor transport strength) of AR conditions under RCP8.5: ~50% (25%) globally, ~50% (20%) in the northern midlatitudes, and ~60% (20%) in the southern midlatitudes (Figure 2).

Figure 2 from Espinoza et al., 2018. AR frequency (shading; percent of time steps) and IVT (vectors; kg · m−1 · s−1) for (a) ERA‐Interim reanalysis for the historical period (1979–2002) with six green boxes depicting regions analyzed in Figures S2 and S3, (b) the MMM for the 21 CMIP5 models analyzed in this study for the historical period (1979–2002), (c) RCP4.5 warming scenario (2073–2096), and (d) RCP8.5 warming scenario (2073–2096).

This research was supported by the NASA Energy and Water cycle Study (NEWS) program. Vicky Espinoza’s contribution to this study was made possible by NASA Jet Propulsion Laboratory’s Year-Round Internship Program during her graduate studies at the University of Southern California. Please contact Duane Waliser at with inquiries. More information can be found from the NASA website

Espinoza, V., Waliser, D. E., Guan, B., Lavers, D. A., & Ralph, F. M. 2018: Global Analysis of Climate Change Projection Effects on Atmospheric Rivers. Geophysical Research Letters. 45.