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Climatology of extreme daily precipitation in Colorado

CW3E Publication Notice

Climatology of extreme daily precipitation in Colorado and its diverse spatial and seasonal variability

May 5, 2015

Seasonality of the top 10 daily precipitation events measured at Colorado COOP stations that have at least 30 years of data since 1950. Circles represent totals of 10 events. Seasons shaded as winter (DJF; blue), spring (MAM; yellow), summer (JJA; red), and fall (SON; green). Terrain elevation (m; gray shading) as in legend at left; Continental Divide shown by dashed black line.

The origins of extreme precipitation events in the Western U.S. range from landfalling atmospheric rivers, to the summer monsoon, upslope storms on the Rocky Mountain Front Range, and deep convection of the Great Plains variety. This was shown by an analysis across the west of the seasonality of the top 10 wettest days for each of thousands of COOP observer sites (Ralph et al. 2014**). Each of these sites had at least ~10,000 data points, so these top 10 days represent roughly the top 0.1% of days. Some areas were universally dominated by events in one season, or two. A couple of areas stood out in the diversity of their seasonality of extreme daily precipitation, including Colorado.

The study presented in Mahoney et al. 2015* explores this local variability more deeply, explores how the devastating flood of September 2013 in Colorado’s northern Front Range is related, and describes some of the implications of the findings for flood control and other sensitive sectors. The co-authors represent a diverse group themselves, including climate, weather, hydrology, hydrometeorology expertise from several organizations, (CIRES, NOAA/PSD, Scripps/CW3E and CSU). The paper is highlighted here as it represents an example of work on extreme events in the Western U.S. that the Center for Western Weather and Water Extremes is contributing to.

Abstract of Mahoney et al. 2015*: The climatology of Colorado’s historical extreme precipitation events shows a remarkable degree of seasonal and regional variability. Analysis of the largest historical daily-precipitation totals at COOP stations across Colorado by season indicates that the largest recorded daily precipitation totals have ranged from less than 60 mm/day in some areas to greater than 250 mm/day in others. East of the Continental Divide winter events are rarely among the top 10 events at a given site, but spring events dominate in and near the foothills; summer events are most common across the lower-elevation eastern plains, while fall events are most typical for the lower elevations west of the Divide. The seasonal signal in Colorado’s central mountains is complex; high-elevation intense precipitation events have occurred in all months of the year, including summer when precipitation is more likely to be liquid (as opposed to snow) which poses more of an instantaneous flood risk.

*Mahoney, K., F.M. Ralph, K. Wolter, N. Doesken, M. Dettinger, D. Gottas, T. Coleman, and A. White, 2015: Climatology of extreme daily precipitation in Colorado and its diverse spatial and seasonal variability. J. Hydrometeor. 16, 781-792.

** Ralph, F. M., M. Dettinger, A. White, D. Reynolds, D. Cayan, T. Schneider, R. Cifelli, K. Redmond, M. Anderson, F. Gherke, J. Jones, K. Mahoney, L. Johnson, S. Gutman, V. Chandrasekar, J. Lundquist, N.P. Molotch, L. Brekke, R. Pulwarty, J. Horel, L. Schick, A. Edman, P. Mote, J. Abatzoglou, R. Pierce and G. Wick, 2014: A vision for future observations for Western U.S. extreme precipitation and flooding– Special Issue of J. Contemporary Water Resources Research and Education, Universities Council for Water Resources, Issue 153, pp. 16-32.

Sonoma County Water Agency and CW3E — Monitoring sites expected to improve forecast capability

Sonoma County Water Agency and CW3E — Monitoring sites expected to improve forecast capability<

September 2013

South end of Lake Mendocino; September 2013 (photo by Kent Porter / Press Democrat)

The Santa Rosa Press Democrat (Sean Scully) published an article: “Weather forecasting a key concern for Sonoma County Water Agency”. CW3E is working with the Sonoma County Water Agency and the Hydrometeorology Testbed (HMT) data to improve forecasts in the region. The data being gathered from HMT will lead to improved forecasting of Atmospheric River (AR) events. These events are significant rain producers in the region and strongly impact how water is managed. Better management would lead to storage that could help prevent extremely low lake levels (as shown at Lake Mendocino above). Please find the full Press Democrat article here.

Test Beds Linking Research and Forecasting

September 10, 2013

A new article written by Marty Ralph and colleagues was recently published in the Bulletin of the American Meteorological Society focusing on the emergence of weather-related test beds. The paper provides a brief background on how these test beds successfully bridged the gap between research and forecasting operations; summarizes test bed origins, methods and selected accomplishments; and provides a perspective on the future of test beds. A personal use copy of the paper can be obtained here.

“Atmospheric Rivers”: Rising Interest in Science and the Media

April 25, 2015

The term “atmospheric river” was first coined in 1994 to describe atmospheric water vapor transport across the mid-latitudes. Subsequent research has shown them to be responsible for the majority of extreme hydrologic events in the western United States, Europe, and South America, as well as being critical to water resources in these regions.

A recent analysis conducted by Ann Coppin and Duane Waliser of NASA’s Jet Propulsion Laboratory and Marty Ralph of Scripps Institution Of Oceanography’s CW3E has highlighted the growing number of journal publications using the term “atmospheric rivers”, illustrating a growing use for this terminology (see figure below).

The number of publications using the term “atmospheric river” from 1994-2013

The number of references across different media outlets has also risen underscoring the increasing public interest in this phenomenon (see figure below).

The number of times the term “atmospheric river” has been used across various media outlets from 2005-2015

1st ARTMIP Workshop held at SIO

1^st ARTMIP Workshop held at SIO

May 15, 2017

The 1^st Atmospheric River Tracking Method Intercomparison Project (ARTMIP) Workshop was recently held at the Scripps Institute of Oceanography in La Jolla, CA. The participants consisted of an ad-hoc group of researchers working to identify and track atmospheric rivers (ARs), elongated regions of atmospheric water vapor transport that contribute significantly to high-impact weather events and hydroclimate. The American Meteorological Society has recently accepted a qualitative definition of what constitutes an AR, but many differences in AR identification and tracking algorithms exist. One goal of the meeting was to discuss key science questions that arise from these methods – most of these are questions related to uncertainty regarding AR climatology, the relationship between ARs and precipitation, and how these may be altered under future climate change scenarios. Another goal of the meeting was to reach consensus on common data sets and metrics to facilitate a quantitative comparison of these AR identification and tracking methods.

The 1^st ARTMIP Workshop was a resounding success, featuring ~20 participants from a wide variety of institutions. ARTMIP participants agreed upon a two-tiered structure for the project. Tier 1 describes the core of the ARTMIP project – common metrics that all participants have agreed to pursue. This analysis will be based on participants applying their AR identification and tracking methods to a common reanalysis data set (MERRA version 2) a period of record (1980-2016), with selected years and/or individual events also investigated. Data provided by each participant will be used to produce global and regional analyses of AR climatology and contributions to precipitation. Tier 2 describes a wide range or related analyses that will be conducted by subgroups within ARTMIP. Analyses will focus on addressing specific science questions such as how and why AR climatology varies in different regions, what are the relationships between AR and precipitation extremes, and how much do ARs contribute to poleward moisture transport globally.

The group will produce at least two papers based on Tier 1 metrics. The first will be submitted to Geoscientific Model Development (GMD) and will describe the Tier 1 experimental design and possible Tier 2 projects, as well as invite the wider community to participate in the ARTMIP. Christine Shields of NCAR will lead this paper, which will be written in the very near timeframe (mid 2017). The second paper will describe the comparative results across methods for AR climatology that are obtained through the Tier 1 analysis. Jon Rutz of the NWS will lead this paper, to be submitted to BAMS (or a similar high-profile journal) in about a year (mid to late 2018).

There are multiple Tier 2 analyses to be performed and these will comprise several additional papers. While Tier 1 focuses on uncertainty amongst the different tracking method algorithms, Tier 2 will explore other sources of uncertainty, such as the uncertainty that arises from different reanalysis products (ERA-interim, NCEP, CFSR and JRA55) and the uncertainty that arises in future climate change projections of ARs.

We have at least three proposed Tier 2 analyses focusing on climate model products. The first is to compare 25, 100, and 200 km CAM5 All-Hist (cesm1_0_3) output from the C20C+ Sub-project on Detection and Attribution (portal.nersc.gov/c20c) to explore uncertainty across model resolution. This is a different issue than the simple coarsening of the reanalysis data. The second climate model Tier 2 analysis is an actual climate change experiment that will analyze the historical and rcp8.5 25 km CAM5 simulations produced for the C20C+ (high-resolution is likely to be very important in replicating atmospheric river climatology and properties). A third experiment is to analyze CMIP5 ensemble results to explore structural uncertainty of projected changes in AR statistics. However, this is contingent on obtaining the large volume of data that must be downloaded from the ESGF. As has seen before, high frequency data can take months to assemble from the ESGF.

Jon Rutz (NOAA/NWS) and Christine Shields (NCAR) serve as ARTMIP co-chairs, while Michael Wehner (LBNL), Ruby Leung (PNNL), and Marty Ralph (UCSD) serve with them on the project committee. A second ARTMIP workshop will be held in mid- to late 2018 to discuss the results of the intercomparison and the implications for the science of Atmospheric Rivers.

Workshop Participants (left to right): Sasha Gershunov, Beth McClenny, Roger Pierce, Anna Wilson, Bin Guan, Ashley Payne, Juan Lora, Duane Waliser, Marty Ralph, Paul Ullrich, Ruby Leung, Michael Wehner, Christine Shields, Jon Rutz, Aneesh Subramanian, Scott Sellars.

Resilience in a Changing Climate: Sonoma County Adaptation Forum

April 15, 2015

CW3E director Marty Ralph and scientist Julie Kalansky presented at the Sonoma County Adaptation Forum on April 8th. The forum was modeled after state forums, but was the first regional adaptation forum in California. The forum focused on information and approaches to help mitigate the impacts of climate change in Sonoma County and surrounding areas. The audience of over 200 people included city and county leaders, utility managers, environmental groups and the public.

Both Marty and Julie presented in the first session of the morning entitled “Extreme Weather Science; Drought and Deluge in Sonoma County.” Jay Jasperse, Chief Engineer and Director of Groundwater Management at Sonoma County Water Agency, moderated the session. The other panelists included Tim Doherty, from NOAA’s Office for Coastal Management, who discussed the impacts of sea level rise on the region, and Dr. Lisa Micheli, Executive Director of Pepperwood Preserve, who presented on the importance of downscaling climate models to understand the regional response to climate change. Marty Ralph discussed the importance of atmospheric rivers (ARs) to the water supply as well as the potential flooding risk associated with ARs. This led into an explanation of the FIRO, forecast informed reservoir operations, project for improving the water supply resilience of Lake Mendocino. At the end of his presentation he introduced the first part of an ongoing NOAA-NIDIS and Sonoma County Water Agency funded project to examine how the frequency and intensity of ARs may change in future. The link below is to an interview with Marty Ralph about atmospheric rivers and the forum that was broadcasted on North Bay Public Radio.

http://radio.krcb.org/post/charting-local-adaptations-climate-change

After Marty’s presentation, Julie presented on the second part of the study including the development of a “mega-drought” stress test for the region and working with the community to understand the all the different dimensions of drought. During Julie’s presentation, she was able to involve the audience and received feedback on the vulnerabilities to drought and the difficult decisions that surround drought. The day was a great success in bringing together scientists, decisions makers and the public to discuss how to make the community more resilient to climate change.

CW3E Welcomes Brian Kawzenuk

CW3E welcomes Brian Kawzenuk

March 30, 2015

CW3E is pleased to welcome Brian Kawzenuk as a staff research associate. Brian joins us from completing his master’s work with Dr. Jason Cordeira at Plymouth State University in New Hampshire. At Plymouth Brian investigated the impacts of land-falling atmospheric rivers (ARs) on the west coast during February 2014. The structure and dynamics of AR events as well as their influence on extreme precipitation over the west coast were explored. Brian looks forward to continuing his study of AR events and using his extensive analytic and programming skills to help the CW3E team develop stakeholder tools. Brian grew up in central New York State and has always had a passion for meteorology. We’re delighted to welcome him to the team and hope he enjoys the milder climate of the La Jolla region.

Sonoma County Water Agency video posted about Atmospheric Rivers

Sonoma County Water Agency (SWCA) Video posted about Atmospheric Rivers (ARs)

March 4, 2015

CW3E is pleased to be part of a recent video produced by our partners at the Sonoma County Water Agency (SCWA) and hosted by SCWA Director Shirlee Zane. This video focuses on the importance of Atmospheric Rivers (ARs) to California’s precipitation. Extremes of both drought and flood are examined for their link to ARs and impact on the Sonoma region. Emphasis is placed on the importance of understanding ARs and applying that knowledge to create better forecast information to help SCWA prepare for drought and potential flood conditions. Shirlee points out a key goal of our collaboration: “retain water without increasing flood risk”.

DWR Video posted about CalWater and ARs

February 27, 2015

CW3E is pleased to be part of a recent video produced by Elissa Lynn, program manager at California’s Department of Water Resources (a CW3E partner). This video focuses on the recent CalWater 2015 – ACAPEX Field Campaign and the importance of Atmospheric Rivers (ARs) to California’s precipitation. This video provides excellent background information about ARs and how unique CalWater 2015 was with the availability of 4 different aircrafts and a NOAA research vessel examining ARs simultaneously. The importance of atmospheric aerosols from humans and their potential link to precipitation quantity is also described in this video.

California Precipitation: summary handout

February 8, 2015

Coefficient of variation (the standard deviation divided by the average) of total precipitation based on water year data from 1951-2008.

Please click here for the summary handout

CW3E and partners from the California Department of Water Resources, CNAP and the Southwest Climate Science Center have released a summary handout describing California precipitation. The seasonality and variability of precipitation for the state are examined in this summary. Special emphasis is on the link between large storms (AR storms) and the total precipitation for a season. The figure above (Dettinger et al., 2011) illustrates that how much variability there is from year to year in precipitation. The green and blue circles over California indicate the largest year-to-year variability is over this state at an order of about half the annual average precipitation.