Exceptional Drought - California Nevada Climate Applications

Climate.gov news article:
The drought-busting benefits of atmospheric rivers
Atmospheric rivers are the source of 30-50% of precipitation along the US west coast.
Read more at:
2014 cumulative discharge 41% below
average: Merced River at Happy Isles
Photo taken by CNAP researcher
Kelly Redmond
Yosemite Falls; April 22, 2014
Merced River daily
discharge – has the
flow peaked for 2014?
Photo taken by CNAP researcher
Kelly Redmond
Merced River; April 23, 2014
Merced River flow for
the past week has been
near the 98-year median
values. CNAP researcher
Mike Dettinger notes
flow has rarely been
above 1000cfs this year
– the normal pulse for
the Merced is near
2000cfs. Mike also
points out very little
snow is left at low to
mid altitudes.
Photo taken by CNAP researcher
Kelly Redmond
Merced River; April 24, 2014
The road over Tioga Pass in Yosemite opened on May 5. This is the earliest opening
date since 1988. Shown above are opening dates since 1933 and the April 1 snow
water equivalent (SWE) at Tioga Pass since 1930. 2014 values are in red.
California Drought Forum
15-16 May 2014
Sacramento, CA
Making Decisions in Dry Times:
Science and Strategies for Dealing with Drought
More information:
Exceptional Drought: Intensification of drought
The 29 April drought monitor continues D4 (exceptional) drought conditions
over portions of west central California. A considerable portion of the state
remains under D3 (extreme) drought conditions.
California and Nevada Drought is extreme to exceptional
The percent of normal precipitation since early November 2013 shows most of the
west below normal with areas of California and Nevada less than 50% of normal.
The percent of precipitation over the last TWO years shows much of
California and Nevada at less than 70% of normal.
Randall Osterhuber at the Central Sierra Snow Laboratory (CSSL) recently
updated the above plot showing the snow depth in cm during five of the
DRIEST years on record. Note the current dry year (red; 2014) is on par with
the previous 5 driest years. CSSL records go back over 110 years.
The Northern Sierra Precipitation 8-station index remains below
the amount at this time last year (2012-13). Note last year
ended below normal.
Las Vegas 365-day precipitation deficit: 71% of normal
San Francisco 365-day precipitation deficit: 46% of normal
From CNAP researcher David Pierce:
Observed water yearto-date precipitation
Note swath of unusually low
precipitation along the entire
west coast.
This “dot” plot shows station
precipitation percentile. Each dot shows
a station that has reported data in the
last 30 days (data from the GHCN). The
values reflect the amount of
precipitation that has fallen since
October 1, 2013. A value of 50% is
normal (a light green dot). Dark brown
with a heavy black outline shows
unusually low precipitation.
California reservoirs
are well below
normal in the
central to northern
regions of the state.
Blue numbers show
percent of capacity. Red
numbers show percent
of historical average.
High pressure has
dominated the eastern
Pacific since October 2013
October through
December 2013
October 2013 through
April 2014
Some rain is possible over the California/Nevada region from
May 6th to 11th
How do the recent northern rainfalls look from a hydrologic
point of view? Folsom Lake is a reservoir east of Sacramento
Reservoir storage since March of 2009; before recent storms at 170,000
AF (acre-feet) and now at 284,000 AF – a 14% bump up from the storms
compared to the desired near-peak storage of 930,000 AF.
How much water is flowing into Folsom Lake?
During the storms
the inflow
reached a
maximum near
25,000 CFS (cubic
feet per second).
The current inflow
rate is about
1,800 CFS; before
the storms the
inflow rate was
about 300 CFS.
How long would it take to fill Folsom Lake to a desired 930,000 AF level?
Inflow rate (CFS)
Time to fill (days)
CA climate
division 5:
Just one year
makes it
above 75% of
Can we recover from the drought? Chances are slim …
To get an idea of the likelihood of recovery from drought status CNAP researcher Mike Dettinger starts
with the precipitation deficit from last year (water year 2012-2013). The black squares show what has
been observed (added to the deficit) since October (2013; O on the x-axis). The total precipitation is
shown on the y-axis and green lines indicate the values as percent of normal.
% of normal by
Oct 2014
Can we recover from the drought?
Chances are slim …
The above histograms summarize the chances of drought recovery for the 7 California climate
divisions. Starting with the water deficit from 2012-13 the percent of years that reach normal
are tabulated above. The red inverted triangle indicates the historical even odds of where
water year 2013-14 may end.
CNAP researcher Mike Dettinger provides us with a look at our ability to reach a normal
amount of precipitation this water year. The above map shows the number of years when
there was enough rain from January through September to compensate for the lack of
rain in the fall. Note western US sites recovered in the fewest number of years.
CNAP researcher Mike Dettinger also provides us with a longer-range look at our ability to reach a
normal amount of precipitation considering last water year was also dry. The above map shows the
number of years when there was enough rain from January through September to compensate for the
lack of rain from the previous fall. Note western US sites, especially in California, rarely recovered.

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