Author: cw3e-web

CW3E Publication Notice: Evaluation of the Subseasonal Forecast Skill of Floods Associated with Atmospheric Rivers in Coastal Western US Watersheds

CW3E Publication Notice

Evaluation of the Subseasonal Forecast Skill of Floods Associated with Atmospheric Rivers in Coastal Western US Watersheds

April 30, 2021

UCLA and now CW3E post-doc, Qian Cao, along with UCSB researcher Shraddhanand Shukla, CW3E researcher Michael J. DeFlorio, CW3E Director F. Martin Ralph, and UCLA Professor Dennis Lettenmaier, recently published a paper in the Journal of Hydrometeorology titled “Evaluation of the subseasonal forecast skill of floods associated with atmospheric rivers in coastal Western US watersheds” ( Cao et al., 2021). The research aligns with the Subseasonal to Seasonal Prediction of Extreme Weather Priority Area within CW3E’s 2019-2024 Strategic Plan because it evaluates the NOAA’s SubX-driven AR-related flood forecast skill along the U.S. West Coast.

Atmospheric rivers (ARs) are responsible for up to 90% of major flood events along the U.S. West Coast (Ralph et al. 2019). The timescale of subseasonal forecasting (two weeks to one month) is a critical lead time for proactive mitigation of flood disasters. The NOAA/Climate Testbed Subseasonal Experiment (SubX) is a research-to-operations project with almost immediate availability of forecasts. It has produced a reforecast database that facilitates evaluation of flood forecasts at these subseasonal lead times. Here, they examine the SubX driven forecast skill of AR-related flooding out to 4-week lead using the Distributed Hydrology Soil Vegetation Model (DHSVM), with particular attention to the role of antecedent soil moisture (ASM), which modulates the relationship between meteorological and hydrological forecast skill. They study three watersheds along a transect of the U.S. West Coast: the Chehalis River basin in Washington, the Russian River basin in Northern California, and the Santa Margarita River basin in Southern California.

They find that the SubX driven flood forecast skill drops quickly after week 1, during which there is relatively high deterministic forecast skill. They find some probabilistic forecast skill relative to climatology as well as ensemble streamflow prediction (ESP) in week 2, but minimal skill in weeks 3-4, especially for annual maximum floods, notwithstanding some probabilistic skill for smaller floods in week 3 (see Fig. 1). Using ESP and reverse-ESP experiments to consider the relative influence of ASM and SubX reforecast skill, they find that ASM dominates probabilistic forecast skill only for small flood events at week 1, while SubX reforecast skill dominates for large flood events at all lead times.

The research support to co-authors of this paper was provided by the CW3E at the Scripps Institution of Oceanography UC San Diego via AR Program Phase II, sponsored by the California Department of Water Resources, and NOAA Regional Integrated Sciences and Assessments (RISA)’s support through the California–Nevada Applications Program.

Figure 1: a) SubX-based Brier skill score (BSS; denoted as “BSSSubX” and shown as square symbols) over weeks 1-4 lead time for Peaks Over Threshold of POTN1 (denoted as “BSSPOTN1”) and POTN3 (denoted as “BSSPOTN3”) extreme discharge events (with threshold set to 1 and 3 events per year on average). The boxplot shows a 90% confidence interval of their differences (denoted as “△BSSPOTN3-POTN1”) derived by bootstrapping. The case when there is no overlapping with zero indicates that the difference is significant. b) Difference between the BSSSubX and the ESP-based BSS (denoted as “△BSSSubX-ESP”), and difference between the BSSSubX and the NCEP_ESP (i.e. the NCEP is used for weeks 1-2 and ESP for weeks 3-4) -based BSS (denoted as “△BSSSubX-NCEP_ESP”) for POTN1 events. c) Same as b) but for POTN3 events.
 

Cao, Q., S. Shukla, M.J. DeFlorio, F.M. Ralph, and D.P. Lettenmaier, 2021: Evaluation of the subseasonal forecast skill of floods associated with atmospheric rivers in coastal Western U.S. watersheds, J. Hydrometeor., https://doi.org/ 10.1175/JHM-D-20-0219.1

CW3E Publication Notice: A Climatological Study of National Weather Service Watches, Warnings, and Advisories and Landfalling Atmospheric Rivers in the Western U.S. 2006–2018

CW3E Publication Notice

A Climatological Study of National Weather Service Watches, Warnings, and Advisories and Landfalling Atmospheric Rivers in the Western U.S. 2006–2018

April 30, 2021

Samuel Bartlett, a student at Plymouth State University, recently published a paper (Bartlett and Cordeira, 2021) in Weather and Forecasting with co-author and close CW3E collaborator, Plymouth State University professor Jason Cordeira.

As part of an effort to quantify the benefit-hazard spectrum of landfalling ARs and leverage the Ralph et al. (2019) AR scale, the study used 13 years of NWS watch, warning, and advisory (WWA) data to illustrate the relationships between landfalling ARs and potentially hazardous weather across the western US. This study contributes to the goals of CW3E’s 2019-2024 Strategic Plan to support Atmospheric River (AR) Research and Applications by quantifying the relationship between AR rank (strength and duration) and the AR’s potential hazard footprint, providing critical information to support decision makers in the west.

While a WWA is not necessarily a storm report and is influenced by local thresholds, climate, and possibly forecast best practices across WFOs, it does provide a lens into where hazardous weather was at least locally anticipated associated with landfalling ARs. The study quantifies and summarizes the following five key points at forecast zones across the west:

  • A majority of WWAs issued in advance of potentially hazardous weather across the western US occur in association with landfalling ARs
  • WWAs issued in advance of potentially hazardous weather are increasingly more likely to occur in association with more intense and longer duration ARs (i.e., as AR scale increases)
  • Not all landfalling ARs necessarily require WWAs (i.e., not all ARs are hazardous)
  • More intense and longer duration ARs are more likely to require WWAs as compared to less intense and shorter duration ARs (i.e., more intense and longer duration ARs are more hazardous)
  • The hazard footprint of landfalling ARs, especially for “hydrologic hazards”, increases exponentially as AR scale increases

Based on the results of this study, a similar smaller study by Cordeira et al. (2018), the results from Corringham et al. (2019; exponential increase in flood damages following AR scale), and the known influence of antecedent conditions on hazards (i.e., an AR5 in October on dry soil may not be hazardous), we created the following schematic illustrating a benefit-hazard spectrum for the AR scale (Fig. 1):

Figure 1: Fig. 12 from Bartlett and Cordeira (2021). A generalized schematic illustration of the exponential increase in the potential for hazardous weather in the western U.S., in this study defined by the “hazard footprint” of WWAs and in Corringham et al. (2019) defined by flood damages, associated with the Ralph et al. (2019) AR scale. Text annotation embedded within the schematic is intended to support interpretation, including the influence of antecedent conditions in modulating the potential for hazardous weather.

Bartlett, S. M., & Cordeira, J. M. (2021). A Climatological Study of National Weather Service Watches, Warnings, and Advisories and Landfalling Atmospheric Rivers in the Western U.S. 2006–2018, Weather and Forecasting, https://doi.org/10.1175/WAF-D-20-0212.1.

CW3E Publication Notice: Uncertainty in different precipitation products in the case of two atmospheric river events

CW3E Publication Notice

Uncertainty in different precipitation products in the case of two atmospheric river events

April 28, 2021

Alexandre Ramos, a researcher at the Institute Dom Luiz at the University of Lisbon, recently published a paper (Ramos et al., 2021) in Environmental Research Letters with several co-authors including two from CW3E, Anna Wilson and F. Martin Ralph.

This study uses the Frequent Rainfall Observations on GridS (FROGS) database, which includes satellite, ground-based, and reanalysis daily precipitation products on a 1ox 1o grid. This is the first time this database has been evaluated using atmospheric rivers (ARs). For the ARs examined here, in two different Mediterranean climates (California and the Iberian peninsula), results indicated that products based on in situ observations were most skilled at obtaining accurate precipitation estimates, while satellites were least skilled (Figure 1). Overall, there remains significant underestimation of precipitation, with mean absolute percentage errors reaching up to 100% in the California AR. This study points out the need to develop higher resolution and accurate gridded products to capture the spatial and temporal properties and variability of precipitation due to ARs.

This study contributes to the goals of CW3E’s 2019-2024 Strategic Plan to support Atmospheric River (AR) Research and Applications, and Monitoring and Projections of Climate Variability and Change, by assessing whether existing precipitation observations are sufficient to understand extreme atmospheric rivers.

Figure 1: Error statistics for precipitation linked to the atmospheric river cases in (a) Portugal, and (b) California. The error measures include bias, MAE, MAPE and RMSE, and were computed pooling together all data for all the groups of the regular gridded products (pool_all), and additionally computing the average observational value for each gridpoint and then compared directly with the regular gridded products values (av). PT and US stand for Portugal and western US, respectively. RE indicates reanalysis products; SG indicates satellite and gauge; SO indicates satellite only products; and GO indicates gauge only. (Figure 6 from Ramos et al., 2021).

Ramos, A.M., Roca, R., Soares, P.M.M., Wilson, A.M., Tigo, R.M. & Ralph, F.M. (2021). Uncertainty in different precipitation products in the case of two atmospheric river events. Environmental Research Letters, 16, 045012, https://doi.org/10.1088/1748-9326/abe25b.

CW3E AR Update: 21 April 2021 Outlook

CW3E AR Update: 21 April 2021 Outlook

April 21, 2021

Click here for a pdf of this information.

Multiple Atmospheric Rivers Forecast to impact U.S. West over Next Week

  • Three ARs are forecast to make landfall over different locations across the U.S. West, bringing much needed precipitation to drought-stricken California
  • The first and weakest AR is forecast to bring dissipating, disorganized, and brief AR conditions to Northern California on 24 April, resulting in <1 inch for much of the Northern CA mountains
  • The Second AR is forecast to make landfall on the 25th, bringing as much as 2 inches of precipitation to Northern California
  • The third AR is forecast to make landfall over the Pacific Northwest on April 28th and could bring IVT magnitudes >700 kg m–1 s–1 to coastal Oregon, though ensemble uncertainty is currently high

Click images to see loops of GFS IVT & IWV forecasts

Valid 1200 UTC 21 April – 1200 UTC 29 April 2021


 

 

 

 

 

 

 

Summary provided by C. Hecht, C. Castellano, J. Kalansky, and F. M. Ralph; 21 April 2021

*Outlook products are considered experimental

CW3E Welcomes Jose Martinez-Claros

CW3E Welcomes Jose Martinez-Claros

April 21, 2021

Dr. Jose Martinez-Claros (he/him/his) joined CW3E as a postdoctoral scholar in April 2021. He received his BS in Meteorology (2012) from the University of Costa Rica. He later received his MS (2017) and PhD. (2020) degrees in Atmospheric Physics from New Mexico Institute of Mining and Technology, under the advisement of Dr. Richard Sonnenfeld for his MS, and of Dr. David Raymond for his PhD. Jose’s previous research was focused in understanding the low-latitude origins of ARs and their connection to tropical moisture sources. Using dropsonde analysis and 3DVar data assimilation methods, he built a description based on the horizontal transport of mid-level vorticity from the tropics to distinguish moisture convergence from moisture transport.

Jose participated in two airborne field campaigns to investigate convective initiation and development in the tropics during his time as a PhD student, the NASA CPEX (Convective Processes Experiment) campaign in 2017, and NCAR OTREC (Organization of Tropical East Pacific Convection) in 2019. His interest in atmospheric rivers emerged from the analysis of the dropsonde and radar results of two of the CPEX research flights, from which he worked to unravel the mystery behind the genesis of atmospheric rivers in the tropics by combining the concepts and methods used in tropical meteorology, with the conceptual base of atmospheric river research. This resulted in a first-author journal article on the analysis of his results for one of the research flights, including the comparison of in-situ dropsonde and dual-band Doppler radar data with independent NCEP FNL model analysis. Jose’s PhD research characterizes atmospheric river origins from a tropical vorticity perspective, based on the interplay between the governing role played by vorticity on the underlying moisture mechanism in the tropics, and the poleward advection of this vorticity by vertical shear.

Jose will be working under the supervision of Dr. Forest Cannon. He will perform research to support CW3E’s goals of improving the prediction and characterization of atmospheric rivers prior to their impact on the U.S West Coast. In particular, he will be using AR reconnaissance, dropsonde, reanalysis and forecast data to develop a conceptual model of AR evolution from low-to-mid latitudes, taking into account the physical principles behind the mechanism that governs the average behavior of moisture in the tropics. Jose will also support a variety of CW3E’s research objectives, including aiding in AR Recon flight planning and rapid-response case study analyses.

CW3E Publication Notice: Time Since Burning and Rainfall Characteristics Impact Post-Fire Debris-Flow Initiation and Magnitude

CW3E Publication Notice

Time Since Burning and Rainfall Characteristics Impact Post-Fire Debris-Flow Initiation and Magnitude

April 15, 2021

Luke McGuire (University of Arizona) and Nina Oakley (CW3E)

Debris flows can pose serious threats to life and infrastructure downstream of steep, recently burned terrain. Previous studies have shown that, in the first year following a fire, debris flows are often triggered during rainstorms where the peak rainfall intensity exceeds some critical value. However, the effects of fire on soil and vegetation diminish over time as burned landscapes recover and it is not clear how this affects the critical rainfall intensity needed to initiate potentially damaging debris flows.

Figure 1: Location of study area (a) and images of the study area as it recovered over the years
following the fire (b-d).

In this study, we used field measurements to quantify changes in soil and vegetation properties in a burned area in the San Gabriel Mountains, CA, over a 3-year time period as it recovered from a fire (Figure 1). Using a numerical model for debris-flow initiation that was constrained by these field measurements, we were able to estimate that an average rainfall intensity of 15-30 mm/h over a 15-minute time period would be sufficient to produce a debris flow in the first year following fire. However, an average rainfall intensity of greater than 60 mm/h over a 15-minute time period would be needed to generate a debris flow after three years of recovery.

Model results also indicated that, given two different rainstorms with the same 15-minute average rainfall intensity, the recently burned landscape is more likely to produce debris flows in cases where there are short, intense bursts of rainfall (e.g., 1- to 5-minute bursts) relative to cases where rainfall intensity is relatively constant. This highlights the need to explore whether or not particular types of storms may be more or less likely to produce debris flows relative to others given their tendency to deliver extreme precipitation in characteristic ways. In southern California, narrow cold frontal rainbands (NCFRs) are capable of producing short and intense (< 15 minute) periods of rainfall that may be particularly conducive to initiating post-fire debris flows.

Figure 2: (a) Radar image showing a narrow cold frontal rainband (NCFR) moving across southern California, and (b) time series of 1-minute and 15-minute average rainfall intensity at a gauge near the study area associated with the passage of the NCFR.

This work addresses the CW3E priority area of Atmospheric River Research and Applications. In the cool season on the US West Coast, short-duration, high-intensity rainfall capable of producing post-wildfire debris flows often occurs in atmospheric rivers. Identifying the connection between the temporal characteristics of precipitation and debris flows helps target our research efforts on atmospheric rivers to focus on this issue. Additionally, this work addresses the CW3E priority area of Modeling Capabilities in the Western US. The importance of very short duration precipitation bursts in debris-flow response suggests that there are benefits to advancing forecast models to address high temporal resolution precipitation. This work also advances the development of debris-flow models for the western US, especially for considering the recovery process. This research was supported by a NOAA CSTAR award and was a collaborative effort among University of Arizona, USGS, UCSD/CW3E, and AZ Geological Survey researchers, highlighting the CW3E Core Value of Collaboration.

Luke A. McGuire, Francis K. Rengers, Nina Oakley, Jason W. Kean, Dennis M. Staley, Hui Tang, Marian de Orla-Barile, Ann M. Youberg; Time Since Burning and Rainfall Characteristics Impact Post-Fire Debris-Flow Initiation and Magnitude. Environmental and Engineering Geoscience, 2021; 27(1): 43-56. doi: https://doi.org/10.2113/EEG-D-20-00029. click here for personal use pdf

CW3E End of Winter Summary: WY 2021

CW3E End of Winter Summary: WY 2021

April 7, 2021

Click here for a pdf of this information.

Water Year 2021 Characterized by Persistent Dry Weather and Worsening Drought in California

  • Total precipitation has been well below normal throughout much of California during water year (WY) 2021
  • In some regions, drier than normal conditions extend back to the start of WY 2020
  • Drought has expanded and intensified across the state, and current water storage levels are below normal in many reservoirs
  • Below-normal snowpack in the Sierra Nevada may limit water resource availability as summer approaches
  • The abnormally dry conditions were driven by a lack of landfalling atmospheric rivers (ARs) and persistent ridging/blocking over the Northeast Pacific Ocean
  • Drought is expected to continue through spring 2021, thereby increasing the threat of significant wildfire activity in summer 2021


 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by C. Castellano, C. Hecht, J. Kalansky, N. Oakley, A. O’Donnell, and F. M. Ralph; 7 April 2021

CW3E Welcomes Qian Cao

CW3E Welcomes Qian Cao

April 2, 2021

Dr. Qian Cao joined CW3E as a postdoctoral research scholar in April 2021. She received her B.S. (2011) and M.S. (2013) degrees in Water Resources Engineering from Wuhan University in China. In March 2020, she received her Ph.D. degree in Geography at University of California, Los Angeles under the advisement of Prof. Dennis Lettenmaier. After that, she continued to work at the UCLA land surface hydrology group as a postdoc for one year prior to joining CW3E.

Qian has been working closely with CW3E since 2016. Her prior research work includes examination of the role of hydrological initial conditions in the linkage between flooding and atmospheric rivers (ARs) in coastal Western U.S. watersheds in a changing climate, evaluation of the AR-related flood forecast skill driven by recently developed data sets such as SubX and West-WRF, as well as investigation of the benefits from remote sensing products in hydrologic applications. Her expertise is hydrological modeling and analysis. She has experience with models like DHSVM, VIC and Noah-MP.

At CW3E, Qian will be working with the hydrology group under the supervision of Dr. Ming Pan. Also, she will be working closely with Dr. Adrian Borsa’s geodesy group. Her research activities will involve using hydrologic models and methods to investigate variability in regional terrestrial water storage, in the form of ground water and surface water including snowpack, as revealed by a growing archive of GPS near-surface crustal displacements that are collected throughout California and across the U.S. She will also be working on the hydrological modeling using WRF-Hydro over the Western U.S. to support the FIRO project.

CW3E Publication Notice: The role of air‐sea interactions in atmospheric rivers: Case studies using the SKRIPS regional coupled model

CW3E Publication Notice

The Role of Air‐sea Interactions in Atmospheric Rivers: Case Studies Using the SKRIPS Regional Coupled Model

March 31, 2021

Rui Sun, a postdoc at CW3E, recently published a paper (Sun et al., 2021) in the Journal of Geophysical Research: Atmospheres along with co-authors from CW3E/Scripps (Aneesh C. Subramanian, Bruce D. Cornuelle, Matthew R. Mazloff, Arthur J. Miller, F. Martin Ralph), Woods Hole Oceanographic Institution (Hyodae Seo), and King Abdullah University of Science and Technology (Ibrahim Hoteit). This study contributes to the goals of CW3E’s 2019-2024 Strategic Plan to support Atmospheric River (AR) Research and Applications, and Subseasonal to Seasonal Prediction of Extreme Weather, by developing and testing a coupled modeling system to improve atmospheric river prediction on a sub-seasonal to seasonal scale.

Given the high societal impact of ARs, it is critical to improve our understanding and prediction of ARs. This study uses a regional coupled ocean–atmosphere modeling system to make hindcasts of ARs up to 14 days. Two groups of coupled runs are highlighted in the comparison: (1) ARs occurring during times with strong SST cooling and (2) ARs occurring during times with weak SST cooling. During the events with strong SST cooling, the coupled model simulates strong upward air–sea heat fluxes associated with ARs; on the other hand, when the SST cooling is weak, the coupled model simulates downward air–sea heat fluxes in the AR region.

Validation data shows that the coupled model skillfully reproduces the evolving SST, as well as the surface turbulent heat transfers between the ocean and atmosphere. The roles of air–sea interactions in AR events are investigated by comparing coupled model hindcasts to hindcasts made using persistent sea surface temperature (SST). To evaluate the influence of the ocean on ARs we analyze two representative variables of AR intensity, the vertically integrated water vapor (IWV) and integrated vapor transport (IVT). During strong SST cooling AR events the simulated IWV is improved by about 12% in the coupled run at lead times greater than one week. For IVT, which is about twice more variable, the improvement in the coupled run is about 5%.

In this work, we used a regional model to show that for runs out to 14 days coupling to an ocean model improved the simulation of AR characteristics. Future work will involve exploring the response of SST to the atmosphere and ocean state (e.g., heat fluxes, wind stress, mixed layer deepening), the impact of the annual SST cycle, and other characteristics of ARs (e.g., AR intensity, orientation) on the coupling.

Figure 1: The schematic description of the SKRIPS regional coupled ocean–atmosphere model. The yellow block is the ESMF/NUOPC coupler; the white blocks are the ocean and atmosphere components; the red blocks are the implemented MITgcm–ESMF and WRF–ESMF interfaces.

Figure 2: Comparison of BSSIWV and BSSIVT between the coupled run and uncoupled run driven by persistent SST. The simulation results are validated using ERA5. Panels (a) and (b) show BSSIWV and BSSIVT, respectively. The markers are the mean BSSs and the error bars are the standard errors of the mean. The inset figures are the box plots of the BSSs that shows the median, the upper/lower quartiles, and the maximum/minimum RMSEs.

Sun, R., Subramanian, A. C., Cornuelle, B. D., Mazloff, M. R., Miller, A. J., Ralph, F. M., et al. (2021). The role of air‐sea interactions in atmospheric rivers: Case studies using the SKRIPS regional coupled model. Journal of Geophysical Research: Atmospheres, 126, e2020JD032885. https://doi.org/10.1029/2020JD032885.

CW3E Welcomes Duncan Axisa

CW3E Welcomes Duncan Axisa

March 17, 2021

Dr. Duncan Axisa joined CW3E as a Program Manager in March 2021. He will support senior management in leadership and direction of the Center’s growing research and applications capabilities, by assisting in developing and executing program research goals. Duncan will provide critical support to the Forecast Informed Reservoir Operations (FIRO) program: a key activity that develops new science, technology, and numerical modeling tools to aid future reservoir operations for flood control, water supply, and ecosystems.

Duncan has extensive experience leading scientific programs, multi-institutional collaborative efforts to design major experiments and research centered on aerosol-cloud-precipitation interactions. After spending a decade at the National Center for Atmospheric Research’s Research Applications Laboratory (RAL) Hydrometeorological Applications Program and several years in a scientific company, Duncan has served the science community in highly collaborative, entrepreneurial, and externally funded research and technology transfer roles. As a scientist, Duncan’s experience focuses on measurements of aerosol, cloud, and precipitation properties, and in evaluating the performance of numerical models. Among his main scientific accomplishments are measurements of the impacts of pollution aerosols on clouds in the Sierra Nevada, characterization of aerosol-cloud interactions in premonsoon and monsoon clouds in South Asia, microphysical interactions of dust with pollution and clouds in Saudi Arabia, observations and modeling of convection-associated dust outbreaks over the Arabian Peninsula, measurements of newly formed particles in the mid-latitude upper troposphere, and source identification of ice nucleating particles. He has participated in over 30 field campaigns including NASA- and NSF-funded studies of aerosol impacts on clouds and precipitation. As a capacity builder Duncan has provided support to developing countries and water stressed communities to help centers establish their own research base. As an innovator he has developed new sensing technologies and holds a patent on intelligent systems.

Duncan holds a BEd from University of Malta, BS in Meteorology and MS in Atmospheric Science from Texas A&M University, and a PhD in Engineering from University of Denver.