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 duane.waliser@jpl.nasa.gov with inquiries. More information can be found from the NASA website https://www.jpl.nasa.gov/news/news.php?feature=7141.

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. https://doi.org/10.1029/2017GL076968

CW3E Undergraduate Student Presents Research at Conference

CW3E Undergraduate Student Presents Research at Conference

May 8, 2018

Cody Poulsen, is a soon to be graduate student with CW3E at Scripps Institution of Oceanography, UC San Diego. During his undergraduate career at UCSD he collaborated on a research project with ex-CW3E post-doc Scott Sellars. The project began during the summer of 2016 and was focused on using a program created by the Monterey Bay Aquarium Research Institute (MBARI) named Video Annotation Reference Systems (VARS) to produce useable meteorological metadata. VARS was created by MBARI to aid researchers in cataloguing the occurrences of biological species and geological formations in the large amounts of underwater footage collected by their ROVs. The research continued as part of Cody’s senior thesis during which he created an Atmospheric River metadata set with VARS. During the process, he learned more about the system and its capabilities. The metadata set is comprised of annotations for the location of AR landfall and center of AR events during the Water Years (WYs) 2001 and 2011. In addition, annotations for ARs with an associated Lower Level Jet (LLJ) structure where produced for both WYs. In the case study of WYs 2001 and 2011, the metadata depicted an anomalously high amount of landfalling AR events in California/Oregon for December 2010 juxtaposed to zero landfalling events along the North American West Coast excluding Alaska for December 2000. 500-hPa average wind speeds, heights, & direction plots for the two months where created to discern the general first principal flow that might explain the different AR trajectories. With these plots, it was found that a high-pressure ridge at 180° and low pressure trough at 140°W funneled ARs onto the California/Oregon coast for December 2010. Where December 2000 had a slight high pressure ridge along the coast to produce an insignificant blocking action leading to the assumption that some other synoptic features must be at play to produce the zero-event period.

Cody produced a poster on the VARS research project and presented it at the Association for Environmental Health and Sciences Foundation (AEHS), 28th Annual International Conference on Soil, Water, Energy, & Air, held in San Diego, CA. His research was presented at the conference’s 14th Annual Student Competition and was selected by the competition committee to receive the second-place award. In addition, to receiving the award Cody was invited to the AEHS appreciation dinner where he met with several industry professionals and researchers to network and discuss the future of the environmental field. Overall, the conference was a great experience for Cody to gain more presentation experience. In addition, he received valuable feedback from a wide range of individuals in the environmental field all with diverse backgrounds.

The VARS program is currently being used by Cody and CW3E post-doc Rachel Weihs to further study Atmospheric Rivers and their impacts on the western coast of the United States of America.

Odds of Reaching 100% Water Year Precipitation – May Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2018 (May Update)

May 2, 2018

Contribution from Dr. M.D. Dettinger, USGS

Here is how we usually tend to see the water-year precip-drought to-date or last month’s contributions represented:

Figure 1: Total precipitation anomaly (large map) and total precipitation (smaller map) during water 2018 (September 2017-April 2018). Images courtesy PRISM Climate Group.

A somewhat different viewpoint on the development of drought considers how much precipitation has fallen (or not) AND how much is likely to fall in coming months, based on climatology. April 2018 produced precipitation over much of northern California and improved odds of reaching normal in some locales, but overall did little to undo the deficits of the previous months in a majority of the state. The following are maps of this year’s drought development that explicitly takes both of these aspects into account.

Here is how the drought has evolved so far this water year in terms of the odds of reaching 100% of normal precipitation by end of water-year 2018.

Figure 2: Odds of reaching 100% of water-year normal precipitation totals throughout water-year 2018.

  • Drought conditions have continued to develop across the Southwest, as odds of reaching normal have progressively dwindled month by month. Although April was wet over parts of northern California, it was—arguably—too little too late to set us up for reaching 100% of normal this year, in all but a few locales.

Figure 3 shows the current odds of reaching various fractions (including but not limited to 100%) of water-year-total this year (top row), as well as the corresponding odds prior to April (bottom row).
This approach offers a far different view than the precipitation anomalies of figure 1, emphasizing different “hot spots” of hope & despair.

Figure 3: Odds of water-year 2018 reaching various fractions of water year normal precipitation totals based on water year precipitation through April (top row) and prior to April (bottom row).

Finally, figure 4 is the “flipped” version of the analysis, asking-at each pixel-how large a water-year total precipitation has a 50% (and other exceedances) chance of being equaled or exceeded this year, as of May 1, 2018.

Figure 4: Chance of water-year total precipitation being equaled or exceeded this year.

  • A different color bar is used here to emphasize that the shades now are illustrating something quite different from the previous maps

How the probabilities above were estimated:
At the end of a given month, if we know how much precipitation has fallen to date (in the water year), the amount of precipitation that will be required to close out the water year (on Sept 30) with a water-year total equal to the long-term normal is just that normal amount minus the amount received to date. Thus the odds of reaching normal by the end of the water year are just the odds of precipitation during the remaining of the year equaling or exceeding that remaining amount.

To arrive at the probabilities shown, the precipitation totals for the remaining months of the water year were tabulated in the long-term historical record (WY1948-2017 in these figures) and the number of years in which that precipitation total equaled or exceeded the amount still needed to reach normal were counted. The fraction of years that at least reached that threshold is the probability estimate. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, etc., for these figures.

[One key simplifying assumption goes into estimating the probabilities this way: The assumption that the amount of precipitation that will fall in the remainder of a water year does not depend on the amount that has already fallen in that water year to date. This assumption was tested (across all climate divisions in California, so far) for each month of the year by correlating historical year-to-date amounts with the remainder-of-the-year amounts, and the resulting correlations were never statistically significantly different from zero.]

Contact: Michael Dettinger (USGS)

CW3E Publication Notice: Evaluation of Atmospheric River Predictions by the WRF Model Using Aircraft and Regional Mesonet Observations of Orographic Precipitation and Its Forcing

CW3E Publication Notice

Evaluation of Atmospheric River Predictions by the WRF Model Using Aircraft and Regional Mesonet Observations of Orographic Precipitation and Its Forcing

April 16, 2018

CW3E project scientist Andrew Martin and co-authors have published a study characterizing predictability limits in Atmospheric River (AR) forecasts and apportioning Russian River precipitation forecast errors among vapor transport and orographic precipitation components. The article, titled Evaluation of Atmospheric River Predictions by the WRF Model Using Aircraft and Regional Mesonet Observations of Orographic Precipitation and its Forcing, is now in early online release at the Journal of Hydrometeorology.

This study leveraged airborne dropsonde observations of offshore Atmospheric Rivers completed during the CalWater experiment and the Atmospheric River Observatory at Bodega Bay and Cazadero, CA to verify forecasts of AR properties and their resulting precipitation. Forecasts were created by CW3E’s numerical weather prediction model, West-WRF, and compared to Global Forecast System reforecasts (GFSRe) valid for the same events. Forecast skill in AR properties and precipitation was evaluated at lead times up to 7 days ahead. Notably, the study found that deterministic skill in integrated vapor transport and other related fields degrades (meaning that forecasts created from climatology perform just as well or better) more than 4 days ahead for both models. However, West-WRF improves upon GFSRe skill in IVT at days 1, 2 and 3 ahead (see Fig. 1c).

Figure 1. a) Value added by GFSRe over GFSRe climatology validated against 145 CalWater dropsondes for the variables z500 (blue), IVT (black), IWV (green) and e925 (red). b) as in a, except for West-WRF value added over GFSRe climatology. c) as in b, except reference forecast is GFSRe.

The study also employed a novel forecast error separation technique to apportion precipitation forecast errors among the component caused by vapor transport simulation and orographic precipitation process simulation. Data from the Atmospheric River Observatory was used to demonstrate that West-WRF forecasts of orographic precipitation during landfalling AR are more accurate in simulating both components; but also that West-WRF forecasts of precipitation can be improved by improving the vapor transport component because its orographic precipitation process is accurate. This lends confidence that CW3E’s effort to improve west coast precipitation forecasts by assimilating offshore observations into West-WRF analyses can yield successful results.

Co-authors include Dr. F Martin Ralph, Reuben Demirdjian, Laurel DeHaan, and Dr. Rachel Weihs of CW3E with Dr. David Reynolds of the Cooperative Institute for Research in Environmental Sciences and Dr. Sam Iacobellis of Scripps Institution of Oceanography. The study was funded by the US Army Corps of Engineers, the California Department of Water Resources, and the National Science Foundation XSEDE program.

Odds of Reaching 100% Water Year Precipitation – April Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2018 (April Update)

April 10, 2018

Contribution from Dr. M.D. Dettinger, USGS

Here is how we usually tend to see the water-year precip-drought to-date or last month’s contributions represented:

Figure 1: Total precipitation anomaly (large map) and total precipitation (smaller map) during water 2018 (September 2017-March 2018). Images courtesy PRISM Climate Group.

A somewhat different viewpoint on the development of precipitation drought considers that development to be a matter of both how much precipitation has fallen (or not) already AND how much more is realistically likely to fall in coming months. E.g., March 2018 simultaneously produced helpful additions to this year’s precipitation totals in California AND was disappointingly far from completely undoing the deficits of the preceding months in most of the State. The following are maps of this year’s drought development that explicitly take both of these aspects into account.

Here is how the drought has evolved so far this water year in terms of the odds of reaching 100% of normal precipitation by end of water-year 2018.

Figure 2: Odds of reaching 100% of water-year normal precipitation totals throughout water-year 2018.

  • Notice how drought conditions have developed across the Southwest, as odds of reaching normal have progressively dwindled month by month. Also notice that, although March was wet in California/Nevada, it was—arguably—too little too late to set us up well for reaching 100% of normal this year, in all but a few locales.

The top row in figure 3 shows the current odds of reaching various fractions (including but not limited to 100%) of water-year-total this year.
Also shown are the corresponding odds prior to March (middle row), and the amount that March precip changed the odds (bottom). This approach offers a far different view than the precipitation anomalies of figure 1, emphasizing different “hot spots” of hope & despair.

Figure 3: Odds of water-year 2018 reaching various fractions of water year normal precipitation totals and the change in these odds during March 2018.

Finally, figure 4 is the “flipped” version of the analysis, asking-at each pixel-how large a water-year total precipitation has a 50% (and other exceedances) chance of being equaled or exceeded this year, as of April 1, 2018.

Figure 4: Chance of water-year total precipitation being equaled or exceeded this year.

  • A different color bar is used here to emphasize that the shades now are illustrating something quite different from the previous maps

How the probabilities above were estimated:
At the end of a given month, if we know how much precipitation has fallen to date (in the water year), the amount of precipitation that will be required to close out the water year (on Sept 30) with a water-year total equal to the long-term normal is just that normal amount minus the amount received to date. Thus the odds of reaching normal by the end of the water year are just the odds of precipitation during the remaining of the year equaling or exceeding that remaining amount.

To arrive at the probabilities shown, the precipitation totals for the remaining months of the water year were tabulated in the long-term historical record (WY1948-2017 in these figures) and the number of years in which that precipitation total equaled or exceeded the amount still needed to reach normal were counted. The fraction of years that at least reached that threshold is the probability estimate. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, etc., for these figures.

[One key simplifying assumption goes into estimating the probabilities this way: The assumption that the amount of precipitation that will fall in the remainder of a water year does not depend on the amount that has already fallen in that water year to date. This assumption was tested (across all climate divisions in California, so far) for each month of the year by correlating historical year-to-date amounts with the remainder-of-the-year amounts, and the resulting correlations were never statistically significantly different from zero.]

Contact: Michael Dettinger (USGS)

CW3E AR Update: 03 April 2018 Outlook

CW3E AR Update: 03 April Outlook

April 03, 2018

Click here for a pdf of this information.

Atmospheric river forecast to impact Northern California later this week

  • GFS Ensemble members are currently forecasting a potentially strong to extreme AR over northern and central California later this week
  • Forecast certainty has increased since yesterday but there is still some uncertainty in the onset, duration, and strength of the AR
  • Up to 7 inches of precipitation is forecasted to fall over the Coastal and Sierra Nevada Mtns in CA, OR, and WA
  • The GEFS is currently suggesting high freezing levels for most of this event, which may lead to most of the precipitation falling as rain

Click IVT or IWV image to see loop of 0-126 hour GFS forecast

Valid 0600 UTC 03 April – 1200 UTC 08 April 2018

 

 

 

 

 

 

 

Summary provided by B. Kawzenuk, F.M. Ralph, and C. Hecht; 11 AM PT Tuesday 03 April 2018

*Outlook products are considered experimental

CW3E AR Update: 22 March 2018 Outlook

CW3E AR Update: 22 March Outlook

March 22, 2018

Click here for a pdf of this information.

Update on Atmospheric River Currently Impacting California

  • Precipitation continues to fall across portions of California
  • The AR will begin to propagate southward bringing moderate AR conditions to Orange and San Diego Counties
  • As much as 9.5 inches of precipitation has fallen over the Coastal Mountains of California during the last 48 hours
  • ~3.75 inches of precipitation has fallen over the high elevations of Santa Barbara and Ventura Counties and 3.5 more inches could fall during the remainder of the storm
  • AR conditions are expected to end at ~11 pm PDT (+/– 3 hours) tonight over Southern California

SSMI/SSMIS/AMSR2-derived Integrated Water Vapor (IWV)

Valid 0000 UTC 19 March – 1600 UTC 22 March 2018

Images from CIMSS/Univ. of Wisconsin

Click IVT or IWV image to see loop of 0-48 hour GFS forecast

Valid 1200 UTC 22 March – 1200 UTC 24 March 2018

 

 

 

 

 

 

 

 

Summary provided by C. Hecht, F.M. Ralph, and B. Kawzenuk; 3 PM PT Thursday 22 March 2018

*Outlook products are considered experimental

CW3E Publication Notice: High-Elevation Evapotranspiration Estimates During Drought: Using Streamflow and NASA Airborne Snow Observatory SWE Observations to Close the Upper Tuolumne River Basin Water Balance

CW3E Publication Notice

High-Elevation Evapotranspiration Estimates During Drought: Using Streamflow and NASA Airborne Snow Observatory SWE Observations to Close the Upper Tuolumne River Basin Water Balance

March 5, 2018

CW3E postdoc Brian Henn has published a study on estimating evapotranspiration (ET) in California’s Sierra Nevada in Water Resources Research titled High-Elevation Evapotranspiration Estimates During Drought: Using Streamflow and NASA Airborne Snow Observatory SWE Observations to Close the Upper Tuolumne River Basin Water Balance. The study leveraged NASA Airborne Snow Observatory (ASO) and distributed streamflow observations and a basin-scale mass balance approach to estimate ET across the upper Tuolumne River watershed region over three warm seasons (2013-2015), showing spatially coherent totals of about 200 mm per year of ET for these high-elevation areas during California’s recent drought. This represents a novel application of ASO and mass balance approaches to estimate ET at the watershed scale, which is difficult to observe directly. The Tuolumne watershed and others like it the Sierra Nevada are critical water supply areas for California, and changes in ET in the future could impact the reliability of major reservoirs.

The paper was written in collaboration with Tom Painter and Kat Bormann of the NASA ASO team, Bruce McGurk of McGurk Hydrologic, Lorraine and Alan Flint of the USGS, Vince White of Southern California Edison, and Jessica Lundquist of the University of Washington. Please contact Brian at bhenn@ucsd.edu with inquiries.

Figure 1. Figure (1) from Henn et al. (2018): (a) ASO lidar-derived 50 m SWE map for 3 April 2013, over the basin of the Tuolumne River at Highway 120. (b) Example plot for this ASO flight, showing how the basin’s water balance is quantified. All SWE from the 3 April flight is assumed to melt by 30 September ( math formula); cumulative streamflow ( math formula) and precipitation ( math formula) between the flight date and 30 September are then calculated. Uncertainty bounds at 95% confidence are shown for each variable.

Henn, B., Painter, T. H., Bormann, K. J., McGurk, B., Flint, A. L., Flint, L. E., White, V., Lundquist, J. D. (2018). High-elevation evapotranspiration estimates during drought: Using streamflow and NASA airborne snow observatory SWE observations to close the upper tuolumne river basin water balance. Water Resources Research, 54. https://doi.org/10.1002/2017WR020473

CW3E Publication Notice: Global Assessment of Atmospheric River Prediction Skill

CW3E Publication Notice

Global Assessment of Atmospheric River Prediction Skill

February 27, 2018

CW3E collaborators Michael DeFlorio (NASA/JPL), Duane Waliser (NASA/JPL), and Bin Guan (UCLA), along with CW3E director Marty Ralph and colleagues David Lavers and Frederic Vitart of the European Centre for Medium-Range Weather Forecasts (ECMWF), recently published a paper in the Journal of Hydrometeorology titled Global Assessment of Atmospheric River Prediction Skill (early online release; doi:10.1175/JHM-D-17-0135.1). The study introduces the Atmospheric River Skill (ATRISK) algorithm, which is an object-based approach used to quantify atmospheric river (AR) prediction skill using Subseasonal to Seasonal (S2S) Project global hindcast data from ECMWF. Two decades of data from this ensemble hindcast system were used in this work. The ATRISK algorithm determines the distance between the centroids of observed and forecasted ARs (an adjustable parameter; see Fig. 1), which can be used to compute relative operating characteristic (ROC) curves. DeFlorio et. al (2018) shows that climate variability conditions modulate regional AR forecast skill. In particular, over the US West Coast, AR forecast utility (defined as the ratio of hits to false alarms) decreases at 10-day lead during negative Pacific-North America (PNA) conditions, and increases at 10-day lead during positive El Nino and Southern Oscillation (ENSO) conditions, with an even larger increase in AR forecast skill during phase-locked El Niño and positive PNA conditions (Fig. 2).

Figure 1: Figure (2) from DeFlorio et al. (2018): Method of determining if a predicted atmospheric river (AR) is a “hit” or a “miss” relative to an observed AR. Predicted and observed ARs are shown as shaded light and dark shaded ovals, respectively. Their IVT-weighted centroids are shown as black dots, and the distances D1 and D2 between each predicted AR and the observed AR are shown as black arrows. The distance threshold DT, which indicates the acceptable horizontal distance between an observed and predicted AR for a prediction to be considered skillful, is shown as a black arrow. In this example, the prediction of AR1 is considered skillful (a “hit”) since its centroid falls within the distance threshold of the observed AR, while the prediction of AR2 is not considered skillful (a “miss”) since its centroid falls outside the distance threshold of the observed AR.

Figure 2. Figure (10a) from DeFlorio et al. (2018): Relative operating characteristic (ROC) curves composited on positive (red) and negative (blue) phases of the combined El Niño-Southern Oscillation (ENSO) & Pacific-North America teleconnection (PNA) modes in December-January-February (DJF) over the North Pacific/Western U.S. region. The 1000 km distance threshold is used, and positive and negative phases are defined using +/- 0.5 standardized values of the climate index for each mode. 3-day (solid), 7-day (dashed), and 10-day (dotted) lead times are shown. The number of positive and negative phase days for each combined mode phase are listed above the legend. Area under ROC curve distributions for both region/mode/lead times of relevance, calculated from a bootstrap process that was repeated 1000 times by using resampling of the composite positive and negative mode days (red and blue, respectively) and all days (white) distributions with replacement, are included beside the ROC curves.

Deflorio, M., D. Waliser, B. Guan, D. Lavers, F.M. Ralph, and F. Vitart, 2018: Global assessment of atmospheric river prediction skill. Journal of Hydrometeorology, early online release, doi:10.1175/JHM-D-17-0135.1