CW3E Director Featured in the Water Zone Podcast on KCAA San Bernardino

CW3E Director Featured in the Water Zone Podcast on KCAA San Bernardino

April 25, 2018

The Water Zone is a KCAA (Loma Linda, CA) radio show, hosted by Paul McFadden, that explores water issues in agriculture and farming from various perspectives to advance water conservation. The April 19, 2018 episode featured two notable guests: Dr. F. Martin Ralph, CW3E Director, and Dr. Thomas Philp, a Pulitzer Prize winning journalist who is the executive strategist for the Metropolitan Water District of Southern California.

Follow the link to listen: http://podcasts.kcaastreaming.com/water/20180419.html. Information related to western weather and water can be heard during minutes 11-44 of the episode.

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 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

Odds of Reaching 100% Water Year Precipitation – Jan Update

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

January 8, 2018

Contribution from Dr. M.D. Dettinger, USGS

The odds shown here are the odds of precipitation in the rest of the water year (after December 2017) totaling a large enough amount to bring the water-year total to equal or exceed the percentage of normal listed. “All Yrs” odds based on monthly divisional precipitation totals from water year 1896-2015. Numbers in parenthesis are the corresponding odds if precipitation through December had been precisely normal (1981-2010 baseline).

Click here for a pdf file of this information.

 

 

 

How these probabilities 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 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. This simple calculation was performed for a full range of possible starting months (from November thru September) and for a wide range of initial (year-to-date) precipitation conditions. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, and 150%, to ensure that the resulting tables of probabilities cover almost the full range of situations that will come up in the future.

[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 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, except possibly when the beginning month is March, for which there is a small positive correlation between Oct-Mar and Apr-Sept precipitation historically.]

Contact: Michael Dettinger (USGS)

CW3E AR Outlook: 14 December 2017 Ridge Update

CW3E AR Outlook: 14 December 2017 Ridge Update

December 14, 2017

Click here for a pdf of this information.

Dry Conditions Expected to Persist over CA for the Foreseeable Future

  • Persistent high pressure and ridging over the northeast Pacific and USWC is directing moisture transport towards AK and resulting in long periods of dry conditions over the USWC
  • The lack of precipitation over the southern USWC is increasing drought conditions and has resulted in the Northern Sierra 8-station index dropping below normal accumulations to date
  • While ridging is forecast to persist, AR conditions are currently forecast to impact the West Coast but the unfavorable north/northwesterly orientation of IVT will result in little or no precipitation over CA
  • Click IVT or IWV image to see loop of 0-180 hour GFS forecast

    Valid 1200 UTC 14 December – 0000 UTC 22 December 2017

    Click 500-hPa Geopotential Height & Vorticity image to see loop of 0-180 hour GFS forecast


     

     

     

     

     

     

    Summary provided by C. Hecht, J. Cordeira B. Kawzenuk, J. Kalansky, and F.M. Ralph; 1 PM PT Thursday 14 December 2017

    *Outlook products are considered experimental

Odds of Reaching 100% Water Year Precipitation – Dec Update

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

December 8, 2017

Contribution from Dr. M.D. Dettinger, USGS

The odds shown here are the odds of precipitation in the rest of the water year (after November 2017) totaling a large enough amount to bring the water-year total to equal or exceed the percentage of normal listed. “All Yrs” odds based on monthly divisional precipitation totals from water year 1896-2015. Numbers in parenthesis are the corresponding odds if precipitation through November had been precisely normal (1981-2010 baseline).

Click here for a pdf file of this information.

 

 

 

How these probabilities 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 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. This simple calculation was performed for a full range of possible starting months (from November thru September) and for a wide range of initial (year-to-date) precipitation conditions. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, and 150%, to ensure that the resulting tables of probabilities cover almost the full range of situations that will come up in the future.

[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 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, except possibly when the beginning month is March, for which there is a small positive correlation between Oct-Mar and Apr-Sept precipitation historically.]

Contact: Michael Dettinger (USGS)

Odds of Reaching 100% Water Year Precipitation – Feb Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2017 (February Update)

February 9, 2017

Contribution from Dr. M.D. Dettinger, USGS

The odds shown here are the odds of precipitation in the rest of the water year (after January 2017) totaling a large enough amount to bring the water-year total to equal or exceed the percentage of normal listed. “All Yrs” odds based on monthly divisional precipitation totals from water year 1896-2015. Numbers in parenthesis are the corresponding odds if precipitation through January had been precisely normal (1981-2010 baseline).

Click here for a pdf file of this information.
 

 

 

How these probabilities 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 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. This simple calculation was performed for a full range of possible starting months (from November thru September) and for a wide range of initial (year-to-date) precipitation conditions. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, and 150%, to ensure that the resulting tables of probabilities cover almost the full range of situations that will come up in the future.

[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 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, except possibly when the beginning month is March, for which there is a small positive correlation between Oct-Mar and Apr-Sept precipitation historically.]

Contact: Michael Dettinger (USGS)

Water year 2017 Precipitation

Water year 2017 Precipitation in California

January 24, 2017

The wetness of this winter in northern California has been truly exceptional. Only two past winters on record have had as much precipitation to date as this year has in the Sacramento River watershed, which is key to California water supply. And each of those was a major flood year.

CW3E AR Update: 17 January 2017 Outlook

CW3E AR Update: 17 January 2017 Outlook

January 17, 2017

Click here for a pdf of this information.

Multiple ARs Forecast to Make Landfall Over Next Week

  • Three ARs are currently forecast to make landfall over the U.S. West Coast at different times over the next 5 days
  • The first AR is forecast to make landfall over the Pacific Northwest today and is associated with strong AR conditions (IVT 750–1000 kg/m/s)
  • The second AR is forecast to make landfall over Southern CA from 20 – 22 Jan and is associated with strong AR conditions (IVT 750–1000 kg/m/s)
  • The third AR is forecast to make landfall over Central CA and could potentially be associated with strong AR conditions (IVT 750–1000 kg/m/s)
  • Forecast uncertainty is currently high with both AR 2 and 3
  • Weather Prediction Center precipitation forecasts currently range from 3–9 inches with AR 1, 2–4 inches with AR 2, and 2–5 inches with AR 3


 

 

 

 

 

 

Summary provided by C. Hecht, and F.M. Ralph; 3 PM PT Mon 17 Jan. 2017

Odds of Reaching 100% Water Year Precipitation – Jan Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2017 (January Update)

January 9, 2017

Contribution from Dr. M.D. Dettinger, USGS

The odds shown here are the odds of precipitation in the rest of the water year (after December 2016) totaling a large enough amount to bring the water-year total to equal or exceed the percentage of normal listed. “All Yrs” odds based on monthly divisional precipitation totals from water year 1896-2015. Numbers in parenthesis are the corresponding odds if precipitation through October had been precisely normal (1981-2010 baseline).

Click here for a pdf file of this information.
 

 

 

How these probabilities 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 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. This simple calculation was performed for a full range of possible starting months (from November thru September) and for a wide range of initial (year-to-date) precipitation conditions. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, and 150%, to ensure that the resulting tables of probabilities cover almost the full range of situations that will come up in the future.

[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 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, except possibly when the beginning month is March, for which there is a small positive correlation between Oct-Mar and Apr-Sept precipitation historically.]

Contact: Michael Dettinger (USGS)